Hello,
syzbot found the following crash on:
HEAD commit: 2019fc96 Merge git://git.kernel.org/pub/scm/linux/kernel/g..
git tree: net
console output: https://syzkaller.appspot.com/x/log.txt?x=13aa0229e00000
kernel config: https://syzkaller.appspot.com/x/.config?x=735296e4dd620b10
dashboard link: https://syzkaller.appspot.com/bug?extid=122b5421d14e68f29cd1
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
Unfortunately, I don't have any reproducer for this crash yet.
IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: [email protected]
======================================================
WARNING: possible circular locking dependency detected
5.6.0-rc1-syzkaller #0 Not tainted
------------------------------------------------------
syz-executor.3/16820 is trying to acquire lock:
ffffe8ffffccc040 (&loc_l->lock){....}, at: bpf_common_lru_push_free kernel/bpf/bpf_lru_list.c:516 [inline]
ffffe8ffffccc040 (&loc_l->lock){....}, at: bpf_lru_push_free+0x250/0x5b0 kernel/bpf/bpf_lru_list.c:555
but task is already holding lock:
ffff88808ceda560 (&htab->buckets[i].lock#2){....}, at: __htab_map_lookup_and_delete_batch+0x617/0x1540 kernel/bpf/hashtab.c:1322
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #2 (&htab->buckets[i].lock#2){....}:
__raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
_raw_spin_lock_irqsave+0x95/0xcd kernel/locking/spinlock.c:159
htab_lru_map_delete_node+0xce/0x2f0 kernel/bpf/hashtab.c:593
__bpf_lru_list_shrink_inactive kernel/bpf/bpf_lru_list.c:220 [inline]
__bpf_lru_list_shrink+0xf9/0x470 kernel/bpf/bpf_lru_list.c:266
bpf_lru_list_pop_free_to_local kernel/bpf/bpf_lru_list.c:340 [inline]
bpf_common_lru_pop_free kernel/bpf/bpf_lru_list.c:447 [inline]
bpf_lru_pop_free+0x87c/0x1670 kernel/bpf/bpf_lru_list.c:499
prealloc_lru_pop+0x2c/0xa0 kernel/bpf/hashtab.c:132
__htab_lru_percpu_map_update_elem+0x67e/0xa90 kernel/bpf/hashtab.c:1069
bpf_percpu_hash_update+0x16e/0x210 kernel/bpf/hashtab.c:1585
bpf_map_update_value.isra.0+0x2d7/0x8e0 kernel/bpf/syscall.c:181
generic_map_update_batch+0x41f/0x610 kernel/bpf/syscall.c:1319
bpf_map_do_batch+0x3f5/0x510 kernel/bpf/syscall.c:3348
__do_sys_bpf+0x9b7/0x41e0 kernel/bpf/syscall.c:3460
__se_sys_bpf kernel/bpf/syscall.c:3355 [inline]
__x64_sys_bpf+0x73/0xb0 kernel/bpf/syscall.c:3355
do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
entry_SYSCALL_64_after_hwframe+0x49/0xbe
-> #1 (&l->lock){....}:
__raw_spin_lock include/linux/spinlock_api_smp.h:142 [inline]
_raw_spin_lock+0x2f/0x40 kernel/locking/spinlock.c:151
bpf_lru_list_pop_free_to_local kernel/bpf/bpf_lru_list.c:325 [inline]
bpf_common_lru_pop_free kernel/bpf/bpf_lru_list.c:447 [inline]
bpf_lru_pop_free+0x67f/0x1670 kernel/bpf/bpf_lru_list.c:499
prealloc_lru_pop+0x2c/0xa0 kernel/bpf/hashtab.c:132
htab_lru_map_update_elem+0x65b/0xba0 kernel/bpf/hashtab.c:950
bpf_map_update_value.isra.0+0x61b/0x8e0 kernel/bpf/syscall.c:206
map_update_elem kernel/bpf/syscall.c:1089 [inline]
__do_sys_bpf+0x3163/0x41e0 kernel/bpf/syscall.c:3384
__se_sys_bpf kernel/bpf/syscall.c:3355 [inline]
__x64_sys_bpf+0x73/0xb0 kernel/bpf/syscall.c:3355
do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
entry_SYSCALL_64_after_hwframe+0x49/0xbe
-> #0 (&loc_l->lock){....}:
check_prev_add kernel/locking/lockdep.c:2475 [inline]
check_prevs_add kernel/locking/lockdep.c:2580 [inline]
validate_chain kernel/locking/lockdep.c:2970 [inline]
__lock_acquire+0x2596/0x4a00 kernel/locking/lockdep.c:3954
lock_acquire+0x190/0x410 kernel/locking/lockdep.c:4484
__raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
_raw_spin_lock_irqsave+0x95/0xcd kernel/locking/spinlock.c:159
bpf_common_lru_push_free kernel/bpf/bpf_lru_list.c:516 [inline]
bpf_lru_push_free+0x250/0x5b0 kernel/bpf/bpf_lru_list.c:555
__htab_map_lookup_and_delete_batch+0x8d4/0x1540 kernel/bpf/hashtab.c:1374
htab_lru_map_lookup_and_delete_batch+0x34/0x40 kernel/bpf/hashtab.c:1491
bpf_map_do_batch+0x3f5/0x510 kernel/bpf/syscall.c:3348
__do_sys_bpf+0x1f7d/0x41e0 kernel/bpf/syscall.c:3456
__se_sys_bpf kernel/bpf/syscall.c:3355 [inline]
__x64_sys_bpf+0x73/0xb0 kernel/bpf/syscall.c:3355
do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
entry_SYSCALL_64_after_hwframe+0x49/0xbe
other info that might help us debug this:
Chain exists of:
&loc_l->lock --> &l->lock --> &htab->buckets[i].lock#2
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(&htab->buckets[i].lock#2);
lock(&l->lock);
lock(&htab->buckets[i].lock#2);
lock(&loc_l->lock);
*** DEADLOCK ***
2 locks held by syz-executor.3/16820:
#0: ffffffff89bac240 (rcu_read_lock){....}, at: __htab_map_lookup_and_delete_batch+0x54b/0x1540 kernel/bpf/hashtab.c:1308
#1: ffff88808ceda560 (&htab->buckets[i].lock#2){....}, at: __htab_map_lookup_and_delete_batch+0x617/0x1540 kernel/bpf/hashtab.c:1322
stack backtrace:
CPU: 0 PID: 16820 Comm: syz-executor.3 Not tainted 5.6.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x197/0x210 lib/dump_stack.c:118
print_circular_bug.isra.0.cold+0x163/0x172 kernel/locking/lockdep.c:1684
check_noncircular+0x32e/0x3e0 kernel/locking/lockdep.c:1808
check_prev_add kernel/locking/lockdep.c:2475 [inline]
check_prevs_add kernel/locking/lockdep.c:2580 [inline]
validate_chain kernel/locking/lockdep.c:2970 [inline]
__lock_acquire+0x2596/0x4a00 kernel/locking/lockdep.c:3954
lock_acquire+0x190/0x410 kernel/locking/lockdep.c:4484
__raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
_raw_spin_lock_irqsave+0x95/0xcd kernel/locking/spinlock.c:159
bpf_common_lru_push_free kernel/bpf/bpf_lru_list.c:516 [inline]
bpf_lru_push_free+0x250/0x5b0 kernel/bpf/bpf_lru_list.c:555
__htab_map_lookup_and_delete_batch+0x8d4/0x1540 kernel/bpf/hashtab.c:1374
htab_lru_map_lookup_and_delete_batch+0x34/0x40 kernel/bpf/hashtab.c:1491
bpf_map_do_batch+0x3f5/0x510 kernel/bpf/syscall.c:3348
__do_sys_bpf+0x1f7d/0x41e0 kernel/bpf/syscall.c:3456
__se_sys_bpf kernel/bpf/syscall.c:3355 [inline]
__x64_sys_bpf+0x73/0xb0 kernel/bpf/syscall.c:3355
do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x45c6c9
Code: ad b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 0f 83 7b b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007efeedbcdc78 EFLAGS: 00000246 ORIG_RAX: 0000000000000141
RAX: ffffffffffffffda RBX: 00007efeedbce6d4 RCX: 000000000045c6c9
RDX: 0000000000000038 RSI: 00000000200001c0 RDI: 0000000000000019
RBP: 000000000076bf20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 0000000000000060 R14: 00000000004c2e9b R15: 000000000076bf2c
---
This bug is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at [email protected].
syzbot will keep track of this bug report. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
syzbot has found a reproducer for the following crash on:
HEAD commit: 2019fc96 Merge git://git.kernel.org/pub/scm/linux/kernel/g..
git tree: net
console output: https://syzkaller.appspot.com/x/log.txt?x=1358bb11e00000
kernel config: https://syzkaller.appspot.com/x/.config?x=735296e4dd620b10
dashboard link: https://syzkaller.appspot.com/bug?extid=122b5421d14e68f29cd1
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=14b67d6ee00000
IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: [email protected]
======================================================
WARNING: possible circular locking dependency detected
5.6.0-rc1-syzkaller #0 Not tainted
------------------------------------------------------
syz-executor.4/13544 is trying to acquire lock:
ffffe8ffffcba0b8 (&loc_l->lock){....}, at: bpf_common_lru_push_free kernel/bpf/bpf_lru_list.c:516 [inline]
ffffe8ffffcba0b8 (&loc_l->lock){....}, at: bpf_lru_push_free+0x250/0x5b0 kernel/bpf/bpf_lru_list.c:555
but task is already holding lock:
ffff888094985960 (&htab->buckets[i].lock){....}, at: __htab_map_lookup_and_delete_batch+0x617/0x1540 kernel/bpf/hashtab.c:1322
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #2 (&htab->buckets[i].lock){....}:
__raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
_raw_spin_lock_irqsave+0x95/0xcd kernel/locking/spinlock.c:159
htab_lru_map_delete_node+0xce/0x2f0 kernel/bpf/hashtab.c:593
__bpf_lru_list_shrink_inactive kernel/bpf/bpf_lru_list.c:220 [inline]
__bpf_lru_list_shrink+0xf9/0x470 kernel/bpf/bpf_lru_list.c:266
bpf_lru_list_pop_free_to_local kernel/bpf/bpf_lru_list.c:340 [inline]
bpf_common_lru_pop_free kernel/bpf/bpf_lru_list.c:447 [inline]
bpf_lru_pop_free+0x87c/0x1670 kernel/bpf/bpf_lru_list.c:499
prealloc_lru_pop+0x2c/0xa0 kernel/bpf/hashtab.c:132
__htab_lru_percpu_map_update_elem+0x67e/0xa90 kernel/bpf/hashtab.c:1069
bpf_percpu_hash_update+0x16e/0x210 kernel/bpf/hashtab.c:1585
bpf_map_update_value.isra.0+0x2d7/0x8e0 kernel/bpf/syscall.c:181
generic_map_update_batch+0x41f/0x610 kernel/bpf/syscall.c:1319
bpf_map_do_batch+0x3f5/0x510 kernel/bpf/syscall.c:3348
__do_sys_bpf+0x9b7/0x41e0 kernel/bpf/syscall.c:3460
__se_sys_bpf kernel/bpf/syscall.c:3355 [inline]
__x64_sys_bpf+0x73/0xb0 kernel/bpf/syscall.c:3355
do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
entry_SYSCALL_64_after_hwframe+0x49/0xbe
-> #1 (&l->lock){....}:
__raw_spin_lock include/linux/spinlock_api_smp.h:142 [inline]
_raw_spin_lock+0x2f/0x40 kernel/locking/spinlock.c:151
bpf_lru_list_pop_free_to_local kernel/bpf/bpf_lru_list.c:325 [inline]
bpf_common_lru_pop_free kernel/bpf/bpf_lru_list.c:447 [inline]
bpf_lru_pop_free+0x67f/0x1670 kernel/bpf/bpf_lru_list.c:499
prealloc_lru_pop+0x2c/0xa0 kernel/bpf/hashtab.c:132
__htab_lru_percpu_map_update_elem+0x67e/0xa90 kernel/bpf/hashtab.c:1069
bpf_percpu_hash_update+0x16e/0x210 kernel/bpf/hashtab.c:1585
bpf_map_update_value.isra.0+0x2d7/0x8e0 kernel/bpf/syscall.c:181
generic_map_update_batch+0x41f/0x610 kernel/bpf/syscall.c:1319
bpf_map_do_batch+0x3f5/0x510 kernel/bpf/syscall.c:3348
__do_sys_bpf+0x9b7/0x41e0 kernel/bpf/syscall.c:3460
__se_sys_bpf kernel/bpf/syscall.c:3355 [inline]
__x64_sys_bpf+0x73/0xb0 kernel/bpf/syscall.c:3355
do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
entry_SYSCALL_64_after_hwframe+0x49/0xbe
-> #0 (&loc_l->lock){....}:
check_prev_add kernel/locking/lockdep.c:2475 [inline]
check_prevs_add kernel/locking/lockdep.c:2580 [inline]
validate_chain kernel/locking/lockdep.c:2970 [inline]
__lock_acquire+0x2596/0x4a00 kernel/locking/lockdep.c:3954
lock_acquire+0x190/0x410 kernel/locking/lockdep.c:4484
__raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
_raw_spin_lock_irqsave+0x95/0xcd kernel/locking/spinlock.c:159
bpf_common_lru_push_free kernel/bpf/bpf_lru_list.c:516 [inline]
bpf_lru_push_free+0x250/0x5b0 kernel/bpf/bpf_lru_list.c:555
__htab_map_lookup_and_delete_batch+0x8d4/0x1540 kernel/bpf/hashtab.c:1374
htab_lru_map_lookup_and_delete_batch+0x34/0x40 kernel/bpf/hashtab.c:1491
bpf_map_do_batch+0x3f5/0x510 kernel/bpf/syscall.c:3348
__do_sys_bpf+0x1f7d/0x41e0 kernel/bpf/syscall.c:3456
__se_sys_bpf kernel/bpf/syscall.c:3355 [inline]
__x64_sys_bpf+0x73/0xb0 kernel/bpf/syscall.c:3355
do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
entry_SYSCALL_64_after_hwframe+0x49/0xbe
other info that might help us debug this:
Chain exists of:
&loc_l->lock --> &l->lock --> &htab->buckets[i].lock
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(&htab->buckets[i].lock);
lock(&l->lock);
lock(&htab->buckets[i].lock);
lock(&loc_l->lock);
*** DEADLOCK ***
2 locks held by syz-executor.4/13544:
#0: ffffffff89bac240 (rcu_read_lock){....}, at: __htab_map_lookup_and_delete_batch+0x54b/0x1540 kernel/bpf/hashtab.c:1308
#1: ffff888094985960 (&htab->buckets[i].lock){....}, at: __htab_map_lookup_and_delete_batch+0x617/0x1540 kernel/bpf/hashtab.c:1322
stack backtrace:
CPU: 0 PID: 13544 Comm: syz-executor.4 Not tainted 5.6.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x197/0x210 lib/dump_stack.c:118
print_circular_bug.isra.0.cold+0x163/0x172 kernel/locking/lockdep.c:1684
check_noncircular+0x32e/0x3e0 kernel/locking/lockdep.c:1808
check_prev_add kernel/locking/lockdep.c:2475 [inline]
check_prevs_add kernel/locking/lockdep.c:2580 [inline]
validate_chain kernel/locking/lockdep.c:2970 [inline]
__lock_acquire+0x2596/0x4a00 kernel/locking/lockdep.c:3954
lock_acquire+0x190/0x410 kernel/locking/lockdep.c:4484
__raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
_raw_spin_lock_irqsave+0x95/0xcd kernel/locking/spinlock.c:159
bpf_common_lru_push_free kernel/bpf/bpf_lru_list.c:516 [inline]
bpf_lru_push_free+0x250/0x5b0 kernel/bpf/bpf_lru_list.c:555
__htab_map_lookup_and_delete_batch+0x8d4/0x1540 kernel/bpf/hashtab.c:1374
htab_lru_map_lookup_and_delete_batch+0x34/0x40 kernel/bpf/hashtab.c:1491
bpf_map_do_batch+0x3f5/0x510 kernel/bpf/syscall.c:3348
__do_sys_bpf+0x1f7d/0x41e0 kernel/bpf/syscall.c:3456
__se_sys_bpf kernel/bpf/syscall.c:3355 [inline]
__x64_sys_bpf+0x73/0xb0 kernel/bpf/syscall.c:3355
do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x45c6c9
Code: ad b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 0f 83 7b b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007efc51c07c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000141
RAX: ffffffffffffffda RBX: 00007efc51c086d4 RCX: 000000000045c6c9
RDX: 0000000000000038 RSI: 00000000200001c0 RDI: 0000000000000019
RBP: 000000000076c118 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 0000000000000060 R14: 00000000004c2e9b R15: 000000000076c124
On 2/16/20 9:23 PM, Hillf Danton wrote:
>
> On Sun, 16 Feb 2020 04:17:09 -0800
>> syzbot has found a reproducer for the following crash on:
>>
>> HEAD commit: 2019fc96 Merge git://git.kernel.org/pub/scm/linux/kernel/g..
>> git tree: net
>> console output: https://urldefense.proofpoint.com/v2/url?u=https-3A__syzkaller.appspot.com_x_log.txt-3Fx-3D1358bb11e00000&d=DwIDAg&c=5VD0RTtNlTh3ycd41b3MUw&r=DA8e1B5r073vIqRrFz7MRA&m=npe_gMkFnfxt6F5dGLs6zsNHWkYM30LkMFOk1_ZR1w8&s=zrgWcBnddWkMWG2zm-9nC8EwvHMsuqw_-EEXwl23XLg&e=
>> kernel config: https://urldefense.proofpoint.com/v2/url?u=https-3A__syzkaller.appspot.com_x_.config-3Fx-3D735296e4dd620b10&d=DwIDAg&c=5VD0RTtNlTh3ycd41b3MUw&r=DA8e1B5r073vIqRrFz7MRA&m=npe_gMkFnfxt6F5dGLs6zsNHWkYM30LkMFOk1_ZR1w8&s=kbT6Yw89JDoIWSQtlLJ7sjyNoP2Ulud27GNorna1zQk&e=
>> dashboard link: https://urldefense.proofpoint.com/v2/url?u=https-3A__syzkaller.appspot.com_bug-3Fextid-3D122b5421d14e68f29cd1&d=DwIDAg&c=5VD0RTtNlTh3ycd41b3MUw&r=DA8e1B5r073vIqRrFz7MRA&m=npe_gMkFnfxt6F5dGLs6zsNHWkYM30LkMFOk1_ZR1w8&s=U3pdUmrcroaeNsJ9DgFbTlvftQUCUcJ1CW_0NxS8yGA&e=
>> compiler: gcc (GCC) 9.0.0 20181231 (experimental)
>> syz repro: https://urldefense.proofpoint.com/v2/url?u=https-3A__syzkaller.appspot.com_x_repro.syz-3Fx-3D14b67d6ee00000&d=DwIDAg&c=5VD0RTtNlTh3ycd41b3MUw&r=DA8e1B5r073vIqRrFz7MRA&m=npe_gMkFnfxt6F5dGLs6zsNHWkYM30LkMFOk1_ZR1w8&s=TuSfjosRFQW3ArpQwikTtx-dgLLBSMgJfVKtUltqQBM&e=
>>
>> IMPORTANT: if you fix the bug, please add the following tag to the commit:
>> Reported-by: [email protected]
>>
>> ======================================================
>> WARNING: possible circular locking dependency detected
>> 5.6.0-rc1-syzkaller #0 Not tainted
>> ------------------------------------------------------
>> syz-executor.4/13544 is trying to acquire lock:
>> ffffe8ffffcba0b8 (&loc_l->lock){....}, at: bpf_common_lru_push_free kernel/bpf/bpf_lru_list.c:516 [inline]
>> ffffe8ffffcba0b8 (&loc_l->lock){....}, at: bpf_lru_push_free+0x250/0x5b0 kernel/bpf/bpf_lru_list.c:555
>>
>> but task is already holding lock:
>> ffff888094985960 (&htab->buckets[i].lock){....}, at: __htab_map_lookup_and_delete_batch+0x617/0x1540 kernel/bpf/hashtab.c:1322
>>
>> which lock already depends on the new lock.
>>
>>
>> the existing dependency chain (in reverse order) is:
>>
>> -> #2 (&htab->buckets[i].lock){....}:
>> __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
>> _raw_spin_lock_irqsave+0x95/0xcd kernel/locking/spinlock.c:159
>> htab_lru_map_delete_node+0xce/0x2f0 kernel/bpf/hashtab.c:593
>> __bpf_lru_list_shrink_inactive kernel/bpf/bpf_lru_list.c:220 [inline]
>> __bpf_lru_list_shrink+0xf9/0x470 kernel/bpf/bpf_lru_list.c:266
>> bpf_lru_list_pop_free_to_local kernel/bpf/bpf_lru_list.c:340 [inline]
>> bpf_common_lru_pop_free kernel/bpf/bpf_lru_list.c:447 [inline]
>> bpf_lru_pop_free+0x87c/0x1670 kernel/bpf/bpf_lru_list.c:499
>> prealloc_lru_pop+0x2c/0xa0 kernel/bpf/hashtab.c:132
>> __htab_lru_percpu_map_update_elem+0x67e/0xa90 kernel/bpf/hashtab.c:1069
>> bpf_percpu_hash_update+0x16e/0x210 kernel/bpf/hashtab.c:1585
>> bpf_map_update_value.isra.0+0x2d7/0x8e0 kernel/bpf/syscall.c:181
>> generic_map_update_batch+0x41f/0x610 kernel/bpf/syscall.c:1319
>> bpf_map_do_batch+0x3f5/0x510 kernel/bpf/syscall.c:3348
>> __do_sys_bpf+0x9b7/0x41e0 kernel/bpf/syscall.c:3460
>> __se_sys_bpf kernel/bpf/syscall.c:3355 [inline]
>> __x64_sys_bpf+0x73/0xb0 kernel/bpf/syscall.c:3355
>> do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
>> entry_SYSCALL_64_after_hwframe+0x49/0xbe
>>
>> -> #1 (&l->lock){....}:
>> __raw_spin_lock include/linux/spinlock_api_smp.h:142 [inline]
>> _raw_spin_lock+0x2f/0x40 kernel/locking/spinlock.c:151
>> bpf_lru_list_pop_free_to_local kernel/bpf/bpf_lru_list.c:325 [inline]
>> bpf_common_lru_pop_free kernel/bpf/bpf_lru_list.c:447 [inline]
>> bpf_lru_pop_free+0x67f/0x1670 kernel/bpf/bpf_lru_list.c:499
>> prealloc_lru_pop+0x2c/0xa0 kernel/bpf/hashtab.c:132
>> __htab_lru_percpu_map_update_elem+0x67e/0xa90 kernel/bpf/hashtab.c:1069
>> bpf_percpu_hash_update+0x16e/0x210 kernel/bpf/hashtab.c:1585
>> bpf_map_update_value.isra.0+0x2d7/0x8e0 kernel/bpf/syscall.c:181
>> generic_map_update_batch+0x41f/0x610 kernel/bpf/syscall.c:1319
>> bpf_map_do_batch+0x3f5/0x510 kernel/bpf/syscall.c:3348
>> __do_sys_bpf+0x9b7/0x41e0 kernel/bpf/syscall.c:3460
>> __se_sys_bpf kernel/bpf/syscall.c:3355 [inline]
>> __x64_sys_bpf+0x73/0xb0 kernel/bpf/syscall.c:3355
>> do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
>> entry_SYSCALL_64_after_hwframe+0x49/0xbe
>>
>> -> #0 (&loc_l->lock){....}:
>> check_prev_add kernel/locking/lockdep.c:2475 [inline]
>> check_prevs_add kernel/locking/lockdep.c:2580 [inline]
>> validate_chain kernel/locking/lockdep.c:2970 [inline]
>> __lock_acquire+0x2596/0x4a00 kernel/locking/lockdep.c:3954
>> lock_acquire+0x190/0x410 kernel/locking/lockdep.c:4484
>> __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
>> _raw_spin_lock_irqsave+0x95/0xcd kernel/locking/spinlock.c:159
>> bpf_common_lru_push_free kernel/bpf/bpf_lru_list.c:516 [inline]
>> bpf_lru_push_free+0x250/0x5b0 kernel/bpf/bpf_lru_list.c:555
>> __htab_map_lookup_and_delete_batch+0x8d4/0x1540 kernel/bpf/hashtab.c:1374
>> htab_lru_map_lookup_and_delete_batch+0x34/0x40 kernel/bpf/hashtab.c:1491
>> bpf_map_do_batch+0x3f5/0x510 kernel/bpf/syscall.c:3348
>> __do_sys_bpf+0x1f7d/0x41e0 kernel/bpf/syscall.c:3456
>> __se_sys_bpf kernel/bpf/syscall.c:3355 [inline]
>> __x64_sys_bpf+0x73/0xb0 kernel/bpf/syscall.c:3355
>> do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
>> entry_SYSCALL_64_after_hwframe+0x49/0xbe
>>
>> other info that might help us debug this:
>>
>> Chain exists of:
>> &loc_l->lock --> &l->lock --> &htab->buckets[i].lock
>>
>> Possible unsafe locking scenario:
>>
>> CPU0 CPU1
>> ---- ----
>> lock(&htab->buckets[i].lock);
>> lock(&l->lock);
>> lock(&htab->buckets[i].lock);
>> lock(&loc_l->lock);
>>
>> *** DEADLOCK ***
>>
>> 2 locks held by syz-executor.4/13544:
>> #0: ffffffff89bac240 (rcu_read_lock){....}, at: __htab_map_lookup_and_delete_batch+0x54b/0x1540 kernel/bpf/hashtab.c:1308
>> #1: ffff888094985960 (&htab->buckets[i].lock){....}, at: __htab_map_lookup_and_delete_batch+0x617/0x1540 kernel/bpf/hashtab.c:1322
>>
>> stack backtrace:
>> CPU: 0 PID: 13544 Comm: syz-executor.4 Not tainted 5.6.0-rc1-syzkaller #0
>> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
>> Call Trace:
>> __dump_stack lib/dump_stack.c:77 [inline]
>> dump_stack+0x197/0x210 lib/dump_stack.c:118
>> print_circular_bug.isra.0.cold+0x163/0x172 kernel/locking/lockdep.c:1684
>> check_noncircular+0x32e/0x3e0 kernel/locking/lockdep.c:1808
>> check_prev_add kernel/locking/lockdep.c:2475 [inline]
>> check_prevs_add kernel/locking/lockdep.c:2580 [inline]
>> validate_chain kernel/locking/lockdep.c:2970 [inline]
>> __lock_acquire+0x2596/0x4a00 kernel/locking/lockdep.c:3954
>> lock_acquire+0x190/0x410 kernel/locking/lockdep.c:4484
>> __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
>> _raw_spin_lock_irqsave+0x95/0xcd kernel/locking/spinlock.c:159
>> bpf_common_lru_push_free kernel/bpf/bpf_lru_list.c:516 [inline]
>> bpf_lru_push_free+0x250/0x5b0 kernel/bpf/bpf_lru_list.c:555
>> __htab_map_lookup_and_delete_batch+0x8d4/0x1540 kernel/bpf/hashtab.c:1374
>> htab_lru_map_lookup_and_delete_batch+0x34/0x40 kernel/bpf/hashtab.c:1491
>> bpf_map_do_batch+0x3f5/0x510 kernel/bpf/syscall.c:3348
>> __do_sys_bpf+0x1f7d/0x41e0 kernel/bpf/syscall.c:3456
>> __se_sys_bpf kernel/bpf/syscall.c:3355 [inline]
>> __x64_sys_bpf+0x73/0xb0 kernel/bpf/syscall.c:3355
>> do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
>> entry_SYSCALL_64_after_hwframe+0x49/0xbe
>
> Reclaim hash table elememt outside bucket lock.
Thanks for the following patch. Yes, we do have an potential issue
with the above deadlock if LRU hash map is not preallocated.
I am not a RCU expert, but maybe you could you help clarify
one thing below?
>
> --- a/kernel/bpf/hashtab.c
> +++ b/kernel/bpf/hashtab.c
> @@ -1259,6 +1259,7 @@ __htab_map_lookup_and_delete_batch(struc
> u64 elem_map_flags, map_flags;
> struct hlist_nulls_head *head;
> struct hlist_nulls_node *n;
> + struct hlist_nulls_node *node_to_free = NULL;
> unsigned long flags;
> struct htab_elem *l;
> struct bucket *b;
> @@ -1370,9 +1371,10 @@ again_nocopy:
> }
> if (do_delete) {
> hlist_nulls_del_rcu(&l->hash_node);
> - if (is_lru_map)
> - bpf_lru_push_free(&htab->lru, &l->lru_node);
> - else
> + if (is_lru_map) {
> + l->hash_node.next = node_to_free;
> + node_to_free = &l->hash_node;
Here, we change "next" pointer. How does this may impact the existing
parallel map lookup which does not need to take bucket pointer?
> + } else
> free_htab_elem(htab, l);
> }
> dst_key += key_size;
> @@ -1380,6 +1382,12 @@ again_nocopy:
> }
>
> raw_spin_unlock_irqrestore(&b->lock, flags);
> +
> + while (node_to_free) {
> + l = container_of(node_to_free, struct htab_elem, hash_node);
> + node_to_free = node_to_free->next;
> + bpf_lru_push_free(&htab->lru, &l->lru_node);
> + }
> /* If we are not copying data, we can go to next bucket and avoid
> * unlocking the rcu.
> */
>
On 2/18/20 9:44 AM, Yonghong Song wrote:
>
>
> On 2/16/20 9:23 PM, Hillf Danton wrote:
>>
>> On Sun, 16 Feb 2020 04:17:09 -0800
>>> syzbot has found a reproducer for the following crash on:
>>>
>>> HEAD commit: 2019fc96 Merge
>>> git://git.kernel.org/pub/scm/linux/kernel/g..
>>> git tree: net
>>> console output:
>>> https://urldefense.proofpoint.com/v2/url?u=https-3A__syzkaller.appspot.com_x_log.txt-3Fx-3D1358bb11e00000&d=DwIDAg&c=5VD0RTtNlTh3ycd41b3MUw&r=DA8e1B5r073vIqRrFz7MRA&m=npe_gMkFnfxt6F5dGLs6zsNHWkYM30LkMFOk1_ZR1w8&s=zrgWcBnddWkMWG2zm-9nC8EwvHMsuqw_-EEXwl23XLg&e=
>>>
>>> kernel config:
>>> https://urldefense.proofpoint.com/v2/url?u=https-3A__syzkaller.appspot.com_x_.config-3Fx-3D735296e4dd620b10&d=DwIDAg&c=5VD0RTtNlTh3ycd41b3MUw&r=DA8e1B5r073vIqRrFz7MRA&m=npe_gMkFnfxt6F5dGLs6zsNHWkYM30LkMFOk1_ZR1w8&s=kbT6Yw89JDoIWSQtlLJ7sjyNoP2Ulud27GNorna1zQk&e=
>>>
>>> dashboard link:
>>> https://urldefense.proofpoint.com/v2/url?u=https-3A__syzkaller.appspot.com_bug-3Fextid-3D122b5421d14e68f29cd1&d=DwIDAg&c=5VD0RTtNlTh3ycd41b3MUw&r=DA8e1B5r073vIqRrFz7MRA&m=npe_gMkFnfxt6F5dGLs6zsNHWkYM30LkMFOk1_ZR1w8&s=U3pdUmrcroaeNsJ9DgFbTlvftQUCUcJ1CW_0NxS8yGA&e=
>>>
>>> compiler: gcc (GCC) 9.0.0 20181231 (experimental)
>>> syz repro:
>>> https://urldefense.proofpoint.com/v2/url?u=https-3A__syzkaller.appspot.com_x_repro.syz-3Fx-3D14b67d6ee00000&d=DwIDAg&c=5VD0RTtNlTh3ycd41b3MUw&r=DA8e1B5r073vIqRrFz7MRA&m=npe_gMkFnfxt6F5dGLs6zsNHWkYM30LkMFOk1_ZR1w8&s=TuSfjosRFQW3ArpQwikTtx-dgLLBSMgJfVKtUltqQBM&e=
>>>
>>>
>>> IMPORTANT: if you fix the bug, please add the following tag to the
>>> commit:
>>> Reported-by: [email protected]
>>>
>>> ======================================================
>>> WARNING: possible circular locking dependency detected
>>> 5.6.0-rc1-syzkaller #0 Not tainted
>>> ------------------------------------------------------
>>> syz-executor.4/13544 is trying to acquire lock:
>>> ffffe8ffffcba0b8 (&loc_l->lock){....}, at: bpf_common_lru_push_free
>>> kernel/bpf/bpf_lru_list.c:516 [inline]
>>> ffffe8ffffcba0b8 (&loc_l->lock){....}, at:
>>> bpf_lru_push_free+0x250/0x5b0 kernel/bpf/bpf_lru_list.c:555
>>>
>>> but task is already holding lock:
>>> ffff888094985960 (&htab->buckets[i].lock){....}, at:
>>> __htab_map_lookup_and_delete_batch+0x617/0x1540
>>> kernel/bpf/hashtab.c:1322
>>>
>>> which lock already depends on the new lock.
>>>
>>>
>>> the existing dependency chain (in reverse order) is:
>>>
>>> -> #2 (&htab->buckets[i].lock){....}:
>>> __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110
>>> [inline]
>>> _raw_spin_lock_irqsave+0x95/0xcd kernel/locking/spinlock.c:159
>>> htab_lru_map_delete_node+0xce/0x2f0 kernel/bpf/hashtab.c:593
>>> __bpf_lru_list_shrink_inactive kernel/bpf/bpf_lru_list.c:220
>>> [inline]
>>> __bpf_lru_list_shrink+0xf9/0x470 kernel/bpf/bpf_lru_list.c:266
>>> bpf_lru_list_pop_free_to_local kernel/bpf/bpf_lru_list.c:340
>>> [inline]
>>> bpf_common_lru_pop_free kernel/bpf/bpf_lru_list.c:447 [inline]
>>> bpf_lru_pop_free+0x87c/0x1670 kernel/bpf/bpf_lru_list.c:499
>>> prealloc_lru_pop+0x2c/0xa0 kernel/bpf/hashtab.c:132
>>> __htab_lru_percpu_map_update_elem+0x67e/0xa90
>>> kernel/bpf/hashtab.c:1069
>>> bpf_percpu_hash_update+0x16e/0x210 kernel/bpf/hashtab.c:1585
>>> bpf_map_update_value.isra.0+0x2d7/0x8e0 kernel/bpf/syscall.c:181
>>> generic_map_update_batch+0x41f/0x610 kernel/bpf/syscall.c:1319
>>> bpf_map_do_batch+0x3f5/0x510 kernel/bpf/syscall.c:3348
>>> __do_sys_bpf+0x9b7/0x41e0 kernel/bpf/syscall.c:3460
>>> __se_sys_bpf kernel/bpf/syscall.c:3355 [inline]
>>> __x64_sys_bpf+0x73/0xb0 kernel/bpf/syscall.c:3355
>>> do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
>>> entry_SYSCALL_64_after_hwframe+0x49/0xbe
>>>
>>> -> #1 (&l->lock){....}:
>>> __raw_spin_lock include/linux/spinlock_api_smp.h:142 [inline]
>>> _raw_spin_lock+0x2f/0x40 kernel/locking/spinlock.c:151
>>> bpf_lru_list_pop_free_to_local kernel/bpf/bpf_lru_list.c:325
>>> [inline]
>>> bpf_common_lru_pop_free kernel/bpf/bpf_lru_list.c:447 [inline]
>>> bpf_lru_pop_free+0x67f/0x1670 kernel/bpf/bpf_lru_list.c:499
>>> prealloc_lru_pop+0x2c/0xa0 kernel/bpf/hashtab.c:132
>>> __htab_lru_percpu_map_update_elem+0x67e/0xa90
>>> kernel/bpf/hashtab.c:1069
>>> bpf_percpu_hash_update+0x16e/0x210 kernel/bpf/hashtab.c:1585
>>> bpf_map_update_value.isra.0+0x2d7/0x8e0 kernel/bpf/syscall.c:181
>>> generic_map_update_batch+0x41f/0x610 kernel/bpf/syscall.c:1319
>>> bpf_map_do_batch+0x3f5/0x510 kernel/bpf/syscall.c:3348
>>> __do_sys_bpf+0x9b7/0x41e0 kernel/bpf/syscall.c:3460
>>> __se_sys_bpf kernel/bpf/syscall.c:3355 [inline]
>>> __x64_sys_bpf+0x73/0xb0 kernel/bpf/syscall.c:3355
>>> do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
>>> entry_SYSCALL_64_after_hwframe+0x49/0xbe
>>>
>>> -> #0 (&loc_l->lock){....}:
>>> check_prev_add kernel/locking/lockdep.c:2475 [inline]
>>> check_prevs_add kernel/locking/lockdep.c:2580 [inline]
>>> validate_chain kernel/locking/lockdep.c:2970 [inline]
>>> __lock_acquire+0x2596/0x4a00 kernel/locking/lockdep.c:3954
>>> lock_acquire+0x190/0x410 kernel/locking/lockdep.c:4484
>>> __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110
>>> [inline]
>>> _raw_spin_lock_irqsave+0x95/0xcd kernel/locking/spinlock.c:159
>>> bpf_common_lru_push_free kernel/bpf/bpf_lru_list.c:516 [inline]
>>> bpf_lru_push_free+0x250/0x5b0 kernel/bpf/bpf_lru_list.c:555
>>> __htab_map_lookup_and_delete_batch+0x8d4/0x1540
>>> kernel/bpf/hashtab.c:1374
>>> htab_lru_map_lookup_and_delete_batch+0x34/0x40
>>> kernel/bpf/hashtab.c:1491
>>> bpf_map_do_batch+0x3f5/0x510 kernel/bpf/syscall.c:3348
>>> __do_sys_bpf+0x1f7d/0x41e0 kernel/bpf/syscall.c:3456
>>> __se_sys_bpf kernel/bpf/syscall.c:3355 [inline]
>>> __x64_sys_bpf+0x73/0xb0 kernel/bpf/syscall.c:3355
>>> do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
>>> entry_SYSCALL_64_after_hwframe+0x49/0xbe
>>>
>>> other info that might help us debug this:
>>>
>>> Chain exists of:
>>> &loc_l->lock --> &l->lock --> &htab->buckets[i].lock
>>>
>>> Possible unsafe locking scenario:
>>>
>>> CPU0 CPU1
>>> ---- ----
>>> lock(&htab->buckets[i].lock);
>>> lock(&l->lock);
>>> lock(&htab->buckets[i].lock);
>>> lock(&loc_l->lock);
>>>
>>> *** DEADLOCK ***
>>>
>>> 2 locks held by syz-executor.4/13544:
>>> #0: ffffffff89bac240 (rcu_read_lock){....}, at:
>>> __htab_map_lookup_and_delete_batch+0x54b/0x1540
>>> kernel/bpf/hashtab.c:1308
>>> #1: ffff888094985960 (&htab->buckets[i].lock){....}, at:
>>> __htab_map_lookup_and_delete_batch+0x617/0x1540
>>> kernel/bpf/hashtab.c:1322
>>>
>>> stack backtrace:
>>> CPU: 0 PID: 13544 Comm: syz-executor.4 Not tainted
>>> 5.6.0-rc1-syzkaller #0
>>> Hardware name: Google Google Compute Engine/Google Compute Engine,
>>> BIOS Google 01/01/2011
>>> Call Trace:
>>> __dump_stack lib/dump_stack.c:77 [inline]
>>> dump_stack+0x197/0x210 lib/dump_stack.c:118
>>> print_circular_bug.isra.0.cold+0x163/0x172
>>> kernel/locking/lockdep.c:1684
>>> check_noncircular+0x32e/0x3e0 kernel/locking/lockdep.c:1808
>>> check_prev_add kernel/locking/lockdep.c:2475 [inline]
>>> check_prevs_add kernel/locking/lockdep.c:2580 [inline]
>>> validate_chain kernel/locking/lockdep.c:2970 [inline]
>>> __lock_acquire+0x2596/0x4a00 kernel/locking/lockdep.c:3954
>>> lock_acquire+0x190/0x410 kernel/locking/lockdep.c:4484
>>> __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
>>> _raw_spin_lock_irqsave+0x95/0xcd kernel/locking/spinlock.c:159
>>> bpf_common_lru_push_free kernel/bpf/bpf_lru_list.c:516 [inline]
>>> bpf_lru_push_free+0x250/0x5b0 kernel/bpf/bpf_lru_list.c:555
>>> __htab_map_lookup_and_delete_batch+0x8d4/0x1540
>>> kernel/bpf/hashtab.c:1374
>>> htab_lru_map_lookup_and_delete_batch+0x34/0x40
>>> kernel/bpf/hashtab.c:1491
>>> bpf_map_do_batch+0x3f5/0x510 kernel/bpf/syscall.c:3348
>>> __do_sys_bpf+0x1f7d/0x41e0 kernel/bpf/syscall.c:3456
>>> __se_sys_bpf kernel/bpf/syscall.c:3355 [inline]
>>> __x64_sys_bpf+0x73/0xb0 kernel/bpf/syscall.c:3355
>>> do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
>>> entry_SYSCALL_64_after_hwframe+0x49/0xbe
>>
>> Reclaim hash table elememt outside bucket lock.
>
> Thanks for the following patch. Yes, we do have an potential issue
> with the above deadlock if LRU hash map is not preallocated.
>
> I am not a RCU expert, but maybe you could you help clarify
> one thing below?
>
>>
>> --- a/kernel/bpf/hashtab.c
>> +++ b/kernel/bpf/hashtab.c
>> @@ -1259,6 +1259,7 @@ __htab_map_lookup_and_delete_batch(struc
>> u64 elem_map_flags, map_flags;
>> struct hlist_nulls_head *head;
>> struct hlist_nulls_node *n;
>> + struct hlist_nulls_node *node_to_free = NULL;
>> unsigned long flags;
>> struct htab_elem *l;
>> struct bucket *b;
>> @@ -1370,9 +1371,10 @@ again_nocopy:
>> }
>> if (do_delete) {
>> hlist_nulls_del_rcu(&l->hash_node);
>> - if (is_lru_map)
>> - bpf_lru_push_free(&htab->lru, &l->lru_node);
>> - else
>> + if (is_lru_map) {
>> + l->hash_node.next = node_to_free;
>> + node_to_free = &l->hash_node;
>
> Here, we change "next" pointer. How does this may impact the existing
> parallel map lookup which does not need to take bucket pointer?
Thanks for Martin for explanation! I think changing l->hash_node.next is
unsafe here as another thread may execute on a different cpu and
traverse the same list. It will see hash_node.next = NULL and it is
unexpected.
How about the following patch?
diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
index 2d182c4ee9d9..246ef0f2e985 100644
--- a/kernel/bpf/hashtab.c
+++ b/kernel/bpf/hashtab.c
@@ -56,6 +56,7 @@ struct htab_elem {
union {
struct bpf_htab *htab;
struct pcpu_freelist_node fnode;
+ struct htab_elem *link;
};
};
};
@@ -1256,6 +1257,7 @@ __htab_map_lookup_and_delete_batch(struct bpf_map
*map,
void __user *ukeys = u64_to_user_ptr(attr->batch.keys);
void *ubatch = u64_to_user_ptr(attr->batch.in_batch);
u32 batch, max_count, size, bucket_size;
+ struct htab_elem *node_to_free = NULL;
u64 elem_map_flags, map_flags;
struct hlist_nulls_head *head;
struct hlist_nulls_node *n;
@@ -1370,9 +1372,14 @@ __htab_map_lookup_and_delete_batch(struct bpf_map
*map,
}
if (do_delete) {
hlist_nulls_del_rcu(&l->hash_node);
- if (is_lru_map)
- bpf_lru_push_free(&htab->lru, &l->lru_node);
- else
+ if (is_lru_map) {
+ /* l->hnode overlaps with *
l->hash_node.pprev
+ * in memory. l->hash_node.pprev has been
+ * poisoned and nobody should access it.
+ */
+ l->link = node_to_free;
+ node_to_free = l;
+ } else
free_htab_elem(htab, l);
}
dst_key += key_size;
@@ -1380,6 +1387,13 @@ __htab_map_lookup_and_delete_batch(struct bpf_map
*map,
}
raw_spin_unlock_irqrestore(&b->lock, flags);
+
+ while (node_to_free) {
+ l = node_to_free;
+ node_to_free = node_to_free->link;
+ bpf_lru_push_free(&htab->lru, &l->lru_node);
+ }
+
/* If we are not copying data, we can go to next bucket and avoid
* unlocking the rcu.
*/
syzbot has found a reproducer for the following crash on:
HEAD commit: e20d3a05 bpf, offload: Replace bitwise AND by logical AND ..
git tree: bpf
console output: https://syzkaller.appspot.com/x/log.txt?x=1491c481e00000
kernel config: https://syzkaller.appspot.com/x/.config?x=e7d35de59001df38
dashboard link: https://syzkaller.appspot.com/bug?extid=122b5421d14e68f29cd1
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=16ca6c45e00000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=134bae29e00000
Bisection is inconclusive: the first bad commit could be any of:
36a375c6 mailmap: add entry for Tiezhu Yang
95c472ff Documentation/ko_KR/howto: Update a broken link
ff1e81a7 Documentation: build warnings related to missing blank lines after explicit markups has been fixed
5549c202 Documentation/ko_KR/howto: Update broken web addresses
599e6f8d Documentation: changes.rst: update several outdated project URLs
4bfdebd6 docs/locking: Fix outdated section names
d1c9038a Allow git builds of Sphinx
41dcd67e Merge tag 'docs-5.6-2' of git://git.lwn.net/linux
bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=17c6c36ee00000
IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: [email protected]
IPVS: ftp: loaded support on port[0] = 21
======================================================
WARNING: possible circular locking dependency detected
5.5.0-syzkaller #0 Not tainted
------------------------------------------------------
syz-executor198/9748 is trying to acquire lock:
ffffe8ffffc49158 (&l->lock){....}, at: bpf_lru_list_push_free kernel/bpf/bpf_lru_list.c:313 [inline]
ffffe8ffffc49158 (&l->lock){....}, at: bpf_common_lru_push_free kernel/bpf/bpf_lru_list.c:532 [inline]
ffffe8ffffc49158 (&l->lock){....}, at: bpf_lru_push_free+0xe5/0x5b0 kernel/bpf/bpf_lru_list.c:555
but task is already holding lock:
ffff88809f6c3b60 (&htab->buckets[i].lock){....}, at: __htab_map_lookup_and_delete_batch+0x617/0x1540 kernel/bpf/hashtab.c:1322
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #1 (&htab->buckets[i].lock){....}:
__raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
_raw_spin_lock_irqsave+0x95/0xcd kernel/locking/spinlock.c:159
htab_lru_map_delete_node+0xce/0x2f0 kernel/bpf/hashtab.c:593
__bpf_lru_list_shrink_inactive kernel/bpf/bpf_lru_list.c:220 [inline]
__bpf_lru_list_shrink+0xf9/0x470 kernel/bpf/bpf_lru_list.c:266
bpf_percpu_lru_pop_free kernel/bpf/bpf_lru_list.c:416 [inline]
bpf_lru_pop_free+0xa9f/0x1670 kernel/bpf/bpf_lru_list.c:497
prealloc_lru_pop+0x2c/0xa0 kernel/bpf/hashtab.c:132
__htab_lru_percpu_map_update_elem+0x67e/0xa90 kernel/bpf/hashtab.c:1069
bpf_percpu_hash_update+0x16e/0x210 kernel/bpf/hashtab.c:1585
bpf_map_update_value.isra.0+0x2d7/0x8e0 kernel/bpf/syscall.c:181
map_update_elem kernel/bpf/syscall.c:1089 [inline]
__do_sys_bpf+0x3163/0x41e0 kernel/bpf/syscall.c:3384
__se_sys_bpf kernel/bpf/syscall.c:3355 [inline]
__x64_sys_bpf+0x73/0xb0 kernel/bpf/syscall.c:3355
do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
entry_SYSCALL_64_after_hwframe+0x49/0xbe
-> #0 (&l->lock){....}:
check_prev_add kernel/locking/lockdep.c:2475 [inline]
check_prevs_add kernel/locking/lockdep.c:2580 [inline]
validate_chain kernel/locking/lockdep.c:2970 [inline]
__lock_acquire+0x2596/0x4a00 kernel/locking/lockdep.c:3954
lock_acquire+0x190/0x410 kernel/locking/lockdep.c:4484
__raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
_raw_spin_lock_irqsave+0x95/0xcd kernel/locking/spinlock.c:159
bpf_lru_list_push_free kernel/bpf/bpf_lru_list.c:313 [inline]
bpf_common_lru_push_free kernel/bpf/bpf_lru_list.c:532 [inline]
bpf_lru_push_free+0xe5/0x5b0 kernel/bpf/bpf_lru_list.c:555
__htab_map_lookup_and_delete_batch+0x8d4/0x1540 kernel/bpf/hashtab.c:1374
htab_lru_percpu_map_lookup_and_delete_batch+0x37/0x40 kernel/bpf/hashtab.c:1474
bpf_map_do_batch+0x3f5/0x510 kernel/bpf/syscall.c:3348
__do_sys_bpf+0x1f7d/0x41e0 kernel/bpf/syscall.c:3456
__se_sys_bpf kernel/bpf/syscall.c:3355 [inline]
__x64_sys_bpf+0x73/0xb0 kernel/bpf/syscall.c:3355
do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
entry_SYSCALL_64_after_hwframe+0x49/0xbe
other info that might help us debug this:
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(&htab->buckets[i].lock);
lock(&l->lock);
lock(&htab->buckets[i].lock);
lock(&l->lock);
*** DEADLOCK ***
2 locks held by syz-executor198/9748:
#0: ffffffff89bac200 (rcu_read_lock){....}, at: __htab_map_lookup_and_delete_batch+0x54b/0x1540 kernel/bpf/hashtab.c:1308
#1: ffff88809f6c3b60 (&htab->buckets[i].lock){....}, at: __htab_map_lookup_and_delete_batch+0x617/0x1540 kernel/bpf/hashtab.c:1322
stack backtrace:
CPU: 0 PID: 9748 Comm: syz-executor198 Not tainted 5.5.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x197/0x210 lib/dump_stack.c:118
print_circular_bug.isra.0.cold+0x163/0x172 kernel/locking/lockdep.c:1684
check_noncircular+0x32e/0x3e0 kernel/locking/lockdep.c:1808
check_prev_add kernel/locking/lockdep.c:2475 [inline]
check_prevs_add kernel/locking/lockdep.c:2580 [inline]
validate_chain kernel/locking/lockdep.c:2970 [inline]
__lock_acquire+0x2596/0x4a00 kernel/locking/lockdep.c:3954
lock_acquire+0x190/0x410 kernel/locking/lockdep.c:4484
__raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
_raw_spin_lock_irqsave+0x95/0xcd kernel/locking/spinlock.c:159
bpf_lru_list_push_free kernel/bpf/bpf_lru_list.c:313 [inline]
bpf_common_lru_push_free kernel/bpf/bpf_lru_list.c:532 [inline]
bpf_lru_push_free+0xe5/0x5b0 kernel/bpf/bpf_lru_list.c:555
__htab_map_lookup_and_delete_batch+0x8d4/0x1540 kernel/bpf/hashtab.c:1374
htab_lru_percpu_map_lookup_and_delete_batch+0x37/0x40 kernel/bpf/hashtab.c:1474
bpf_map_do_batch+0x3f5/0x510 kernel/bpf/syscall.c:3348
__do_sys_bpf+0x1f7d/0x41e0 kernel/bpf/syscall.c:3456
__se_sys_bpf kernel/bpf/syscall.c:3355 [inline]
__x64_sys_bpf+0x73/0xb0 kernel/bpf/syscall.c:3355
do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x440c09
Code: 18 89 d0 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 0f 83 7b 10 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007fff14512e08 EFLAGS: 00000246 ORIG_RAX: 0000000000000141
RAX: ffffffffffffffda RBX: 00000000004a2390 RCX: 0000000000440c09
RDX: 0000000000000038 RSI: 0000000020000100 RDI: 0000000000000019
RBP: 00000000006cb018 R08: 0000000120080522 R09: 0000000120080522
R10: 0000000120080522 R11: 0000000000000246 R12: 0000000000402110
R13: 00000000004021a0 R14: 0000000000000000 R15: 0000000000000000
On 2/18/20 6:15 PM, Hillf Danton wrote:
>
> Hey
>
> On Tue, 18 Feb 2020 15:55:02 -0800 Yonghong Song wrote:
>>
>> Thanks for Martin for explanation! I think changing l->hash_node.next is
>> unsafe here as another thread may execute on a different cpu and
>> traverse the same list. It will see hash_node.next = NULL and it is
>
> Good catch.
>
>> unexpected.
>>
>> How about the following patch?
>>
> Looks nicer, thanks :P
>
>> diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
>> index 2d182c4ee9d9..246ef0f2e985 100644
>> --- a/kernel/bpf/hashtab.c
>> +++ b/kernel/bpf/hashtab.c
>> @@ -56,6 +56,7 @@ struct htab_elem {
>> union {
>> struct bpf_htab *htab;
>> struct pcpu_freelist_node fnode;
>> + struct htab_elem *link;
>> };
>> };
>> };
>> @@ -1256,6 +1257,7 @@ __htab_map_lookup_and_delete_batch(struct bpf_map *map,
>> void __user *ukeys = u64_to_user_ptr(attr->batch.keys);
>> void *ubatch = u64_to_user_ptr(attr->batch.in_batch);
>> u32 batch, max_count, size, bucket_size;
>> + struct htab_elem *node_to_free = NULL;
>> u64 elem_map_flags, map_flags;
>> struct hlist_nulls_head *head;
>> struct hlist_nulls_node *n;
>> @@ -1370,9 +1372,14 @@ __htab_map_lookup_and_delete_batch(struct bpf_map *map,
>> }
>> if (do_delete) {
>> hlist_nulls_del_rcu(&l->hash_node);
>> - if (is_lru_map)
>> - bpf_lru_push_free(&htab->lru, &l->lru_node);
>> - else
>> + if (is_lru_map) {
>> + /* l->hnode overlaps with *l->hash_node.pprev
>
> nit: looks like you mean l->link
Yes, my previous attempt uses "hnode" and later changed to "link" but
forget to change the comments.
Will post a patch soon.
>
>> + * in memory. l->hash_node.pprev has been
>> + * poisoned and nobody should access it.
>> + */
>> + l->link = node_to_free;
>> + node_to_free = l;
>> + } else
>> free_htab_elem(htab, l);
>> }
>> dst_key += key_size;
>
On Tue, Feb 18, 2020 at 3:56 PM Yonghong Song <[email protected]> wrote:
>
>
>
> On 2/18/20 9:44 AM, Yonghong Song wrote:
> >
> >
> > On 2/16/20 9:23 PM, Hillf Danton wrote:
> >>
> >> On Sun, 16 Feb 2020 04:17:09 -0800
> >>> syzbot has found a reproducer for the following crash on:
> >>>
> >>> HEAD commit: 2019fc96 Merge
> >>> git://git.kernel.org/pub/scm/linux/kernel/g..
> >>> git tree: net
> >>> console output:
> >>> https://urldefense.proofpoint.com/v2/url?u=https-3A__syzkaller.appspot.com_x_log.txt-3Fx-3D1358bb11e00000&d=DwIDAg&c=5VD0RTtNlTh3ycd41b3MUw&r=DA8e1B5r073vIqRrFz7MRA&m=npe_gMkFnfxt6F5dGLs6zsNHWkYM30LkMFOk1_ZR1w8&s=zrgWcBnddWkMWG2zm-9nC8EwvHMsuqw_-EEXwl23XLg&e=
> >>>
> >>> kernel config:
> >>> https://urldefense.proofpoint.com/v2/url?u=https-3A__syzkaller.appspot.com_x_.config-3Fx-3D735296e4dd620b10&d=DwIDAg&c=5VD0RTtNlTh3ycd41b3MUw&r=DA8e1B5r073vIqRrFz7MRA&m=npe_gMkFnfxt6F5dGLs6zsNHWkYM30LkMFOk1_ZR1w8&s=kbT6Yw89JDoIWSQtlLJ7sjyNoP2Ulud27GNorna1zQk&e=
> >>>
> >>> dashboard link:
> >>> https://urldefense.proofpoint.com/v2/url?u=https-3A__syzkaller.appspot.com_bug-3Fextid-3D122b5421d14e68f29cd1&d=DwIDAg&c=5VD0RTtNlTh3ycd41b3MUw&r=DA8e1B5r073vIqRrFz7MRA&m=npe_gMkFnfxt6F5dGLs6zsNHWkYM30LkMFOk1_ZR1w8&s=U3pdUmrcroaeNsJ9DgFbTlvftQUCUcJ1CW_0NxS8yGA&e=
> >>>
> >>> compiler: gcc (GCC) 9.0.0 20181231 (experimental)
> >>> syz repro:
> >>> https://urldefense.proofpoint.com/v2/url?u=https-3A__syzkaller.appspot.com_x_repro.syz-3Fx-3D14b67d6ee00000&d=DwIDAg&c=5VD0RTtNlTh3ycd41b3MUw&r=DA8e1B5r073vIqRrFz7MRA&m=npe_gMkFnfxt6F5dGLs6zsNHWkYM30LkMFOk1_ZR1w8&s=TuSfjosRFQW3ArpQwikTtx-dgLLBSMgJfVKtUltqQBM&e=
> >>>
> >>>
> >>> IMPORTANT: if you fix the bug, please add the following tag to the
> >>> commit:
> >>> Reported-by: [email protected]
> >>>
> >>> ======================================================
> >>> WARNING: possible circular locking dependency detected
> >>> 5.6.0-rc1-syzkaller #0 Not tainted
> >>> ------------------------------------------------------
> >>> syz-executor.4/13544 is trying to acquire lock:
> >>> ffffe8ffffcba0b8 (&loc_l->lock){....}, at: bpf_common_lru_push_free
> >>> kernel/bpf/bpf_lru_list.c:516 [inline]
> >>> ffffe8ffffcba0b8 (&loc_l->lock){....}, at:
> >>> bpf_lru_push_free+0x250/0x5b0 kernel/bpf/bpf_lru_list.c:555
> >>>
> >>> but task is already holding lock:
> >>> ffff888094985960 (&htab->buckets[i].lock){....}, at:
> >>> __htab_map_lookup_and_delete_batch+0x617/0x1540
> >>> kernel/bpf/hashtab.c:1322
> >>>
> >>> which lock already depends on the new lock.
> >>>
> >>>
> >>> the existing dependency chain (in reverse order) is:
> >>>
> >>> -> #2 (&htab->buckets[i].lock){....}:
> >>> __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110
> >>> [inline]
> >>> _raw_spin_lock_irqsave+0x95/0xcd kernel/locking/spinlock.c:159
> >>> htab_lru_map_delete_node+0xce/0x2f0 kernel/bpf/hashtab.c:593
> >>> __bpf_lru_list_shrink_inactive kernel/bpf/bpf_lru_list.c:220
> >>> [inline]
> >>> __bpf_lru_list_shrink+0xf9/0x470 kernel/bpf/bpf_lru_list.c:266
> >>> bpf_lru_list_pop_free_to_local kernel/bpf/bpf_lru_list.c:340
> >>> [inline]
> >>> bpf_common_lru_pop_free kernel/bpf/bpf_lru_list.c:447 [inline]
> >>> bpf_lru_pop_free+0x87c/0x1670 kernel/bpf/bpf_lru_list.c:499
> >>> prealloc_lru_pop+0x2c/0xa0 kernel/bpf/hashtab.c:132
> >>> __htab_lru_percpu_map_update_elem+0x67e/0xa90
> >>> kernel/bpf/hashtab.c:1069
> >>> bpf_percpu_hash_update+0x16e/0x210 kernel/bpf/hashtab.c:1585
> >>> bpf_map_update_value.isra.0+0x2d7/0x8e0 kernel/bpf/syscall.c:181
> >>> generic_map_update_batch+0x41f/0x610 kernel/bpf/syscall.c:1319
> >>> bpf_map_do_batch+0x3f5/0x510 kernel/bpf/syscall.c:3348
> >>> __do_sys_bpf+0x9b7/0x41e0 kernel/bpf/syscall.c:3460
> >>> __se_sys_bpf kernel/bpf/syscall.c:3355 [inline]
> >>> __x64_sys_bpf+0x73/0xb0 kernel/bpf/syscall.c:3355
> >>> do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
> >>> entry_SYSCALL_64_after_hwframe+0x49/0xbe
> >>>
> >>> -> #1 (&l->lock){....}:
> >>> __raw_spin_lock include/linux/spinlock_api_smp.h:142 [inline]
> >>> _raw_spin_lock+0x2f/0x40 kernel/locking/spinlock.c:151
> >>> bpf_lru_list_pop_free_to_local kernel/bpf/bpf_lru_list.c:325
> >>> [inline]
> >>> bpf_common_lru_pop_free kernel/bpf/bpf_lru_list.c:447 [inline]
> >>> bpf_lru_pop_free+0x67f/0x1670 kernel/bpf/bpf_lru_list.c:499
> >>> prealloc_lru_pop+0x2c/0xa0 kernel/bpf/hashtab.c:132
> >>> __htab_lru_percpu_map_update_elem+0x67e/0xa90
> >>> kernel/bpf/hashtab.c:1069
> >>> bpf_percpu_hash_update+0x16e/0x210 kernel/bpf/hashtab.c:1585
> >>> bpf_map_update_value.isra.0+0x2d7/0x8e0 kernel/bpf/syscall.c:181
> >>> generic_map_update_batch+0x41f/0x610 kernel/bpf/syscall.c:1319
> >>> bpf_map_do_batch+0x3f5/0x510 kernel/bpf/syscall.c:3348
> >>> __do_sys_bpf+0x9b7/0x41e0 kernel/bpf/syscall.c:3460
> >>> __se_sys_bpf kernel/bpf/syscall.c:3355 [inline]
> >>> __x64_sys_bpf+0x73/0xb0 kernel/bpf/syscall.c:3355
> >>> do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
> >>> entry_SYSCALL_64_after_hwframe+0x49/0xbe
> >>>
> >>> -> #0 (&loc_l->lock){....}:
> >>> check_prev_add kernel/locking/lockdep.c:2475 [inline]
> >>> check_prevs_add kernel/locking/lockdep.c:2580 [inline]
> >>> validate_chain kernel/locking/lockdep.c:2970 [inline]
> >>> __lock_acquire+0x2596/0x4a00 kernel/locking/lockdep.c:3954
> >>> lock_acquire+0x190/0x410 kernel/locking/lockdep.c:4484
> >>> __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110
> >>> [inline]
> >>> _raw_spin_lock_irqsave+0x95/0xcd kernel/locking/spinlock.c:159
> >>> bpf_common_lru_push_free kernel/bpf/bpf_lru_list.c:516 [inline]
> >>> bpf_lru_push_free+0x250/0x5b0 kernel/bpf/bpf_lru_list.c:555
> >>> __htab_map_lookup_and_delete_batch+0x8d4/0x1540
> >>> kernel/bpf/hashtab.c:1374
> >>> htab_lru_map_lookup_and_delete_batch+0x34/0x40
> >>> kernel/bpf/hashtab.c:1491
> >>> bpf_map_do_batch+0x3f5/0x510 kernel/bpf/syscall.c:3348
> >>> __do_sys_bpf+0x1f7d/0x41e0 kernel/bpf/syscall.c:3456
> >>> __se_sys_bpf kernel/bpf/syscall.c:3355 [inline]
> >>> __x64_sys_bpf+0x73/0xb0 kernel/bpf/syscall.c:3355
> >>> do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
> >>> entry_SYSCALL_64_after_hwframe+0x49/0xbe
> >>>
> >>> other info that might help us debug this:
> >>>
> >>> Chain exists of:
> >>> &loc_l->lock --> &l->lock --> &htab->buckets[i].lock
> >>>
> >>> Possible unsafe locking scenario:
> >>>
> >>> CPU0 CPU1
> >>> ---- ----
> >>> lock(&htab->buckets[i].lock);
> >>> lock(&l->lock);
> >>> lock(&htab->buckets[i].lock);
> >>> lock(&loc_l->lock);
> >>>
> >>> *** DEADLOCK ***
> >>>
> >>> 2 locks held by syz-executor.4/13544:
> >>> #0: ffffffff89bac240 (rcu_read_lock){....}, at:
> >>> __htab_map_lookup_and_delete_batch+0x54b/0x1540
> >>> kernel/bpf/hashtab.c:1308
> >>> #1: ffff888094985960 (&htab->buckets[i].lock){....}, at:
> >>> __htab_map_lookup_and_delete_batch+0x617/0x1540
> >>> kernel/bpf/hashtab.c:1322
> >>>
> >>> stack backtrace:
> >>> CPU: 0 PID: 13544 Comm: syz-executor.4 Not tainted
> >>> 5.6.0-rc1-syzkaller #0
> >>> Hardware name: Google Google Compute Engine/Google Compute Engine,
> >>> BIOS Google 01/01/2011
> >>> Call Trace:
> >>> __dump_stack lib/dump_stack.c:77 [inline]
> >>> dump_stack+0x197/0x210 lib/dump_stack.c:118
> >>> print_circular_bug.isra.0.cold+0x163/0x172
> >>> kernel/locking/lockdep.c:1684
> >>> check_noncircular+0x32e/0x3e0 kernel/locking/lockdep.c:1808
> >>> check_prev_add kernel/locking/lockdep.c:2475 [inline]
> >>> check_prevs_add kernel/locking/lockdep.c:2580 [inline]
> >>> validate_chain kernel/locking/lockdep.c:2970 [inline]
> >>> __lock_acquire+0x2596/0x4a00 kernel/locking/lockdep.c:3954
> >>> lock_acquire+0x190/0x410 kernel/locking/lockdep.c:4484
> >>> __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
> >>> _raw_spin_lock_irqsave+0x95/0xcd kernel/locking/spinlock.c:159
> >>> bpf_common_lru_push_free kernel/bpf/bpf_lru_list.c:516 [inline]
> >>> bpf_lru_push_free+0x250/0x5b0 kernel/bpf/bpf_lru_list.c:555
> >>> __htab_map_lookup_and_delete_batch+0x8d4/0x1540
> >>> kernel/bpf/hashtab.c:1374
> >>> htab_lru_map_lookup_and_delete_batch+0x34/0x40
> >>> kernel/bpf/hashtab.c:1491
> >>> bpf_map_do_batch+0x3f5/0x510 kernel/bpf/syscall.c:3348
> >>> __do_sys_bpf+0x1f7d/0x41e0 kernel/bpf/syscall.c:3456
> >>> __se_sys_bpf kernel/bpf/syscall.c:3355 [inline]
> >>> __x64_sys_bpf+0x73/0xb0 kernel/bpf/syscall.c:3355
> >>> do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
> >>> entry_SYSCALL_64_after_hwframe+0x49/0xbe
> >>
> >> Reclaim hash table elememt outside bucket lock.
> >
> > Thanks for the following patch. Yes, we do have an potential issue
> > with the above deadlock if LRU hash map is not preallocated.
> >
> > I am not a RCU expert, but maybe you could you help clarify
> > one thing below?
> >
> >>
> >> --- a/kernel/bpf/hashtab.c
> >> +++ b/kernel/bpf/hashtab.c
> >> @@ -1259,6 +1259,7 @@ __htab_map_lookup_and_delete_batch(struc
> >> u64 elem_map_flags, map_flags;
> >> struct hlist_nulls_head *head;
> >> struct hlist_nulls_node *n;
> >> + struct hlist_nulls_node *node_to_free = NULL;
> >> unsigned long flags;
> >> struct htab_elem *l;
> >> struct bucket *b;
> >> @@ -1370,9 +1371,10 @@ again_nocopy:
> >> }
> >> if (do_delete) {
> >> hlist_nulls_del_rcu(&l->hash_node);
> >> - if (is_lru_map)
> >> - bpf_lru_push_free(&htab->lru, &l->lru_node);
> >> - else
> >> + if (is_lru_map) {
> >> + l->hash_node.next = node_to_free;
> >> + node_to_free = &l->hash_node;
> >
> > Here, we change "next" pointer. How does this may impact the existing
> > parallel map lookup which does not need to take bucket pointer?
>
> Thanks for Martin for explanation! I think changing l->hash_node.next is
> unsafe here as another thread may execute on a different cpu and
> traverse the same list. It will see hash_node.next = NULL and it is
> unexpected.
>
> How about the following patch?
I think I'm missing some emails here, but overall the patch looks good to me.
>
> diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
> index 2d182c4ee9d9..246ef0f2e985 100644
> --- a/kernel/bpf/hashtab.c
> +++ b/kernel/bpf/hashtab.c
> @@ -56,6 +56,7 @@ struct htab_elem {
> union {
> struct bpf_htab *htab;
> struct pcpu_freelist_node fnode;
> + struct htab_elem *link;
> };
> };
> };
> @@ -1256,6 +1257,7 @@ __htab_map_lookup_and_delete_batch(struct bpf_map
> *map,
> void __user *ukeys = u64_to_user_ptr(attr->batch.keys);
> void *ubatch = u64_to_user_ptr(attr->batch.in_batch);
> u32 batch, max_count, size, bucket_size;
> + struct htab_elem *node_to_free = NULL;
> u64 elem_map_flags, map_flags;
> struct hlist_nulls_head *head;
> struct hlist_nulls_node *n;
> @@ -1370,9 +1372,14 @@ __htab_map_lookup_and_delete_batch(struct bpf_map
> *map,
> }
> if (do_delete) {
> hlist_nulls_del_rcu(&l->hash_node);
> - if (is_lru_map)
> - bpf_lru_push_free(&htab->lru, &l->lru_node);
> - else
> + if (is_lru_map) {
> + /* l->hnode overlaps with *
> l->hash_node.pprev
> + * in memory. l->hash_node.pprev has been
> + * poisoned and nobody should access it.
> + */
> + l->link = node_to_free;
> + node_to_free = l;
> + } else
> free_htab_elem(htab, l);
> }
> dst_key += key_size;
> @@ -1380,6 +1387,13 @@ __htab_map_lookup_and_delete_batch(struct bpf_map
> *map,
> }
>
> raw_spin_unlock_irqrestore(&b->lock, flags);
> +
> + while (node_to_free) {
> + l = node_to_free;
> + node_to_free = node_to_free->link;
> + bpf_lru_push_free(&htab->lru, &l->lru_node);
> + }
> +
> /* If we are not copying data, we can go to next bucket and avoid
> * unlocking the rcu.
> */
>
>