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Date:   Wed, 2 Jan 2019 10:15:18 +0100
From:   luca abeni <luca.abeni@santannapisa.it>
To:     juri.lelli@redhat.com
Cc:     syzbot <syzbot+119ba87189432ead09b4@syzkaller.appspotmail.com>,
        bp@alien8.de, bristot@redhat.com, hpa@zytor.com,
        linux-kernel@vger.kernel.org, luto@kernel.org, mingo@redhat.com,
        peterz@infradead.org, syzkaller-bugs@googlegroups.com,
        tglx@linutronix.de, x86@kernel.org
Subject: Re: WARNING in enqueue_task_dl
Message-ID: <20190102101518.1d21ba0c@sweethome>
In-Reply-To: <0000000000001f4fee057e52b284@google.com>
References: <000000000000b5e346057af4da06@google.com>
        <0000000000001f4fee057e52b284@google.com>
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Sender: linux-kernel-owner@vger.kernel.org
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Hi all,
(and, happy new year to everyone!)

this looks similar to a bug we have seen some time ago (a task
switching from SCHED_OTHER to SCHED_DEADLINE while inheriting a
deadline from a SCHED_DEADLINE task triggers the warning)...

Juri, I think you found a fix for such a bug; has it been committed?


			Thanks,
				Luca

On Mon, 31 Dec 2018 07:02:04 -0800
syzbot <syzbot+119ba87189432ead09b4@syzkaller.appspotmail.com> wrote:

> syzbot has found a reproducer for the following crash on:
> 
> HEAD commit:    195303136f19 Merge tag 'kconfig-v4.21-2' of
> git://git.kern.. git tree:       upstream
> console output:
> https://syzkaller.appspot.com/x/log.txt?x=118af84b400000 kernel
> config:  https://syzkaller.appspot.com/x/.config?x=76d28549be7c27cf
> dashboard link:
> https://syzkaller.appspot.com/bug?extid=119ba87189432ead09b4
> compiler:       gcc (GCC) 9.0.0 20181231 (experimental) syz
> repro:
> https://syzkaller.appspot.com/x/repro.syz?x=10eb7ebf400000 C
> reproducer:   https://syzkaller.appspot.com/x/repro.c?x=14156d77400000
> 
> IMPORTANT: if you fix the bug, please add the following tag to the
> commit: Reported-by:
> syzbot+119ba87189432ead09b4@syzkaller.appspotmail.com
> 
> WARNING: CPU: 0 PID: 9019 at kernel/sched/deadline.c:628  
> setup_new_dl_entity kernel/sched/deadline.c:629 [inline]
> WARNING: CPU: 0 PID: 9019 at kernel/sched/deadline.c:628
> enqueue_dl_entity kernel/sched/deadline.c:1429 [inline]
> WARNING: CPU: 0 PID: 9019 at kernel/sched/deadline.c:628  
> enqueue_task_dl+0x2355/0x3dc0 kernel/sched/deadline.c:1500
> Kernel panic - not syncing: panic_on_warn set ...
> CPU: 0 PID: 9019 Comm: syz-executor280 Not tainted 4.20.0+ #1
> 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+0x1db/0x2d0 lib/dump_stack.c:113
>   panic+0x2cb/0x589 kernel/panic.c:189
>   __warn.cold+0x20/0x4b kernel/panic.c:544
>   report_bug+0x263/0x2b0 lib/bug.c:186
>   fixup_bug arch/x86/kernel/traps.c:178 [inline]
>   fixup_bug arch/x86/kernel/traps.c:173 [inline]
>   do_error_trap+0x11b/0x200 arch/x86/kernel/traps.c:271
>   do_invalid_op+0x37/0x50 arch/x86/kernel/traps.c:290
>   invalid_op+0x14/0x20 arch/x86/entry/entry_64.S:973
> RIP: 0010:setup_new_dl_entity kernel/sched/deadline.c:628 [inline]
> RIP: 0010:enqueue_dl_entity kernel/sched/deadline.c:1429 [inline]
> RIP: 0010:enqueue_task_dl+0x2355/0x3dc0 kernel/sched/deadline.c:1500
> Code: 3c 02 00 0f 85 ba 05 00 00 49 8b b5 50 0a 00 00 e9 53 fa ff ff
> e8 fb f2 64 00 48 8d 4d d8 e9 48 dd ff ff 0f 0b e9 92 f1 ff ff <0f>
> 0b e9 18 f1 ff ff 4c 89 ef 4c 89 95 28 ff ff ff 4c 89 85 30 ff
> RSP: 0018:ffff88809eebfaf8 EFLAGS: 00010002
> RAX: 0000000000000002 RBX: 1ffff11013dd7f6a RCX: dffffc0000000000
> RDX: 000000333cf09f75 RSI: 0000000000000004 RDI: ffff8880ae62d850
> RBP: ffff88809eebfbf8 R08: ffff88807fb0a538 R09: ffff88807fb0a2fc
> R10: ffff88807fb0a580 R11: ffff8880ae62dc7b R12: ffff88807fb0a2c0
> R13: ffff8880ae62ce00 R14: ffff8880ae62ce00 R15: ffff88807fb0a58c
>   enqueue_task+0xb9/0x380 kernel/sched/core.c:730
>   __sched_setscheduler+0xe32/0x1fe0 kernel/sched/core.c:4336
>   sched_setattr kernel/sched/core.c:4394 [inline]
>   __do_sys_sched_setattr kernel/sched/core.c:4570 [inline]
>   __se_sys_sched_setattr kernel/sched/core.c:4549 [inline]
>   __x64_sys_sched_setattr+0x1af/0x2f0 kernel/sched/core.c:4549
>   do_syscall_64+0x1a3/0x800 arch/x86/entry/common.c:290
>   entry_SYSCALL_64_after_hwframe+0x49/0xbe
> RIP: 0033:0x44c829
> Code: e8 8c d8 02 00 48 83 c4 18 c3 0f 1f 80 00 00 00 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 eb c9 fb ff c3 66 2e 0f 1f 84 00 00 00 00
> RSP: 002b:00007f28685e8ce8 EFLAGS: 00000246 ORIG_RAX: 000000000000013a
> RAX: ffffffffffffffda RBX: 00000000006e49f8 RCX: 000000000044c829
> RDX: 0000000000000000 RSI: 0000000020000000 RDI: 0000000000000000
> RBP: 00000000006e49f0 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 00000000006e49fc
> R13: 00007ffd1981c8af R14: 00007f28685e99c0 R15: 0000000000000001
> 
> ======================================================
> WARNING: possible circular locking dependency detected
> 4.20.0+ #1 Not tainted
> ------------------------------------------------------
> syz-executor280/9019 is trying to acquire lock:
> 000000001aef527c ((console_sem).lock){-.-.}, at:
> down_trylock+0x13/0x70 kernel/locking/semaphore.c:136
> 
> but task is already holding lock:
> 000000000ba17b09 (&rq->lock){-.-.}, at: task_rq_lock+0xc8/0x290  
> kernel/sched/core.c:99
> 
> which lock already depends on the new lock.
> 
> 
> the existing dependency chain (in reverse order) is:
> 
> -> #2 (&rq->lock){-.-.}:  
>         __raw_spin_lock include/linux/spinlock_api_smp.h:142 [inline]
>         _raw_spin_lock+0x2f/0x40 kernel/locking/spinlock.c:144
>         rq_lock kernel/sched/sched.h:1149 [inline]
>         task_fork_fair+0xb5/0x7a0 kernel/sched/fair.c:10083
>         sched_fork+0x437/0xb90 kernel/sched/core.c:2359
>         copy_process+0x1ff6/0x8730 kernel/fork.c:1893
>         _do_fork+0x1a9/0x1170 kernel/fork.c:2222
>         kernel_thread+0x34/0x40 kernel/fork.c:2281
>         rest_init+0x28/0x37b init/main.c:409
>         arch_call_rest_init+0xe/0x1b
>         start_kernel+0x882/0x8bd init/main.c:741
>         x86_64_start_reservations+0x29/0x2b
> arch/x86/kernel/head64.c:470 x86_64_start_kernel+0x77/0x7b
> arch/x86/kernel/head64.c:451 secondary_startup_64+0xa4/0xb0
> arch/x86/kernel/head_64.S:243
> 
> -> #1 (&p->pi_lock){-.-.}:  
>         __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110
> [inline] _raw_spin_lock_irqsave+0x95/0xcd
> kernel/locking/spinlock.c:152 try_to_wake_up+0xb9/0x1480
> kernel/sched/core.c:1965 wake_up_process+0x10/0x20
> kernel/sched/core.c:2129 __up.isra.0+0x1c0/0x2a0
> kernel/locking/semaphore.c:262 up+0x13e/0x1c0
> kernel/locking/semaphore.c:187 __up_console_sem+0xb7/0x1c0
> kernel/printk/printk.c:236 console_unlock+0x778/0x11e0
> kernel/printk/printk.c:2426 con_flush_chars drivers/tty/vt/vt.c:3197
> [inline] con_flush_chars drivers/tty/vt/vt.c:3185 [inline]
>         con_write+0xa2/0xb0 drivers/tty/vt/vt.c:3117
>         process_output_block drivers/tty/n_tty.c:593 [inline]
>         n_tty_write+0x497/0x1220 drivers/tty/n_tty.c:2331
>         do_tty_write drivers/tty/tty_io.c:959 [inline]
>         tty_write+0x45b/0x7a0 drivers/tty/tty_io.c:1043
>         __vfs_write+0x116/0xb40 fs/read_write.c:485
>         vfs_write+0x20c/0x580 fs/read_write.c:549
>         ksys_write+0x105/0x260 fs/read_write.c:598
>         __do_sys_write fs/read_write.c:610 [inline]
>         __se_sys_write fs/read_write.c:607 [inline]
>         __x64_sys_write+0x73/0xb0 fs/read_write.c:607
>         do_syscall_64+0x1a3/0x800 arch/x86/entry/common.c:290
>         entry_SYSCALL_64_after_hwframe+0x49/0xbe
> 
> -> #0 ((console_sem).lock){-.-.}:  
>         lock_acquire+0x1db/0x570 kernel/locking/lockdep.c:3841
>         __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110
> [inline] _raw_spin_lock_irqsave+0x95/0xcd
> kernel/locking/spinlock.c:152 down_trylock+0x13/0x70
> kernel/locking/semaphore.c:136 __down_trylock_console_sem+0xa8/0x210
> kernel/printk/printk.c:219 console_trylock+0x15/0xa0
> kernel/printk/printk.c:2242 console_trylock_spinning
> kernel/printk/printk.c:1662 [inline] vprintk_emit+0x351/0x960
> kernel/printk/printk.c:1930 vprintk_default+0x28/0x30
> kernel/printk/printk.c:1958 vprintk_func+0x7e/0x189
> kernel/printk/printk_safe.c:398 printk+0xba/0xed
> kernel/printk/printk.c:1991 __warn+0x9e/0x1d0 kernel/panic.c:526
>         report_bug+0x263/0x2b0 lib/bug.c:186
>         fixup_bug arch/x86/kernel/traps.c:178 [inline]
>         fixup_bug arch/x86/kernel/traps.c:173 [inline]
>         do_error_trap+0x11b/0x200 arch/x86/kernel/traps.c:271
>         do_invalid_op+0x37/0x50 arch/x86/kernel/traps.c:290
>         invalid_op+0x14/0x20 arch/x86/entry/entry_64.S:973
>         setup_new_dl_entity kernel/sched/deadline.c:629 [inline]
>         enqueue_dl_entity kernel/sched/deadline.c:1429 [inline]
>         enqueue_task_dl+0x2355/0x3dc0 kernel/sched/deadline.c:1500
>         enqueue_task+0xb9/0x380 kernel/sched/core.c:730
>         __sched_setscheduler+0xe32/0x1fe0 kernel/sched/core.c:4336
>         sched_setattr kernel/sched/core.c:4394 [inline]
>         __do_sys_sched_setattr kernel/sched/core.c:4570 [inline]
>         __se_sys_sched_setattr kernel/sched/core.c:4549 [inline]
>         __x64_sys_sched_setattr+0x1af/0x2f0 kernel/sched/core.c:4549
>         do_syscall_64+0x1a3/0x800 arch/x86/entry/common.c:290
>         entry_SYSCALL_64_after_hwframe+0x49/0xbe
> 
> other info that might help us debug this:
> 
> Chain exists of:
>    (console_sem).lock --> &p->pi_lock --> &rq->lock
> 
>   Possible unsafe locking scenario:
> 
>         CPU0                    CPU1
>         ----                    ----
>    lock(&rq->lock);
>                                 lock(&p->pi_lock);
>                                 lock(&rq->lock);
>    lock((console_sem).lock);
> 
>   *** DEADLOCK ***
> 
> 3 locks held by syz-executor280/9019:
>   #0: 0000000014b8e16d (rcu_read_lock){....}, at:
> __do_sys_sched_setattr kernel/sched/core.c:4563 [inline]
>   #0: 0000000014b8e16d (rcu_read_lock){....}, at:
> __se_sys_sched_setattr kernel/sched/core.c:4549 [inline]
>   #0: 0000000014b8e16d (rcu_read_lock){....}, at:  
> __x64_sys_sched_setattr+0x144/0x2f0 kernel/sched/core.c:4549
>   #1: 00000000b31ff59d (&p->pi_lock){-.-.}, at:
> task_rq_lock+0x6a/0x290 kernel/sched/core.c:97
>   #2: 000000000ba17b09 (&rq->lock){-.-.}, at:
> task_rq_lock+0xc8/0x290 kernel/sched/core.c:99
> 
> stack backtrace:
> CPU: 0 PID: 9019 Comm: syz-executor280 Not tainted 4.20.0+ #1
> 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+0x1db/0x2d0 lib/dump_stack.c:113
>   print_circular_bug.isra.0.cold+0x1cc/0x28f
> kernel/locking/lockdep.c:1224 check_prev_add
> kernel/locking/lockdep.c:1866 [inline] check_prevs_add
> kernel/locking/lockdep.c:1979 [inline] validate_chain
> kernel/locking/lockdep.c:2350 [inline] __lock_acquire+0x3014/0x4a30
> kernel/locking/lockdep.c:3338 lock_acquire+0x1db/0x570
> kernel/locking/lockdep.c:3841 __raw_spin_lock_irqsave
> include/linux/spinlock_api_smp.h:110 [inline]
> _raw_spin_lock_irqsave+0x95/0xcd kernel/locking/spinlock.c:152
> down_trylock+0x13/0x70 kernel/locking/semaphore.c:136
> __down_trylock_console_sem+0xa8/0x210 kernel/printk/printk.c:219
> console_trylock+0x15/0xa0 kernel/printk/printk.c:2242
> console_trylock_spinning kernel/printk/printk.c:1662 [inline]
> vprintk_emit+0x351/0x960 kernel/printk/printk.c:1930
> vprintk_default+0x28/0x30 kernel/printk/printk.c:1958
> vprintk_func+0x7e/0x189 kernel/printk/printk_safe.c:398
> printk+0xba/0xed kernel/printk/printk.c:1991 __warn+0x9e/0x1d0
> kernel/panic.c:526 report_bug+0x263/0x2b0 lib/bug.c:186
>   fixup_bug arch/x86/kernel/traps.c:178 [inline]
>   fixup_bug arch/x86/kernel/traps.c:173 [inline]
>   do_error_trap+0x11b/0x200 arch/x86/kernel/traps.c:271
>   do_invalid_op+0x37/0x50 arch/x86/kernel/traps.c:290
>   invalid_op+0x14/0x20 arch/x86/entry/entry_64.S:973
> RIP: 0010:setup_new_dl_entity kernel/sched/deadline.c:628 [inline]
> RIP: 0010:enqueue_dl_entity kernel/sched/deadline.c:1429 [inline]
> RIP: 0010:enqueue_task_dl+0x2355/0x3dc0 kernel/sched/deadline.c:1500
> Code: 3c 02 00 0f 85 ba 05 00 00 49 8b b5 50 0a 00 00 e9 53 fa ff ff
> e8 fb f2 64 00 48 8d 4d d8 e9 48 dd ff ff 0f 0b e9 92 f1 ff ff <0f>
> 0b e9 18 f1 ff ff 4c 89 ef 4c 89 95 28 ff ff ff 4c 89 85 30 ff
> RSP: 0018:ffff88809eebfaf8 EFLAGS: 00010002
> RAX: 0000000000000002 RBX: 1ffff11013dd7f6a RCX: dffffc0000000000
> RDX: 000000333cf09f75 RSI: 0000000000000004 RDI: ffff8880ae62d850
> RBP: ffff88809eebfbf8 R08: ffff88807fb0a538 R09: ffff88807fb0a2fc
> R10: ffff88807fb0a580 R11: ffff8880ae62dc7b R12: ffff88807fb0a2c0
> R13: ffff8880ae62ce00 R14: ffff8880ae62ce00 R15: ffff88807fb0a58c
>   enqueue_task+0xb9/0x380 kernel/sched/core.c:730
>   __sched_setscheduler+0xe32/0x1fe0 kernel/sched/core.c:4336
>   sched_setattr kernel/sched/core.c:4394 [inline]
>   __do_sys_sched_setattr kernel/sched/core.c:4570 [inline]
>   __se_sys_sched_setattr kernel/sched/core.c:4549 [inline]
>   __x64_sys_sched_setattr+0x1af/0x2f0 kernel/sched/core.c:4549
>   do_syscall_64+0x1a3/0x800 arch/x86/entry/common.c:290
>   entry_SYSCALL_64_after_hwframe+0x49/0xbe
> RIP: 0033:0x44c829
> Code: e8 8c d8 02 00 48 83 c4 18 c3 0f 1f 80 00 00 00 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 eb c9 fb ff c3 66 2e 0f 1f 84 00 00 00 00
> RSP: 002b:00007f28685e8ce8 EFLAGS: 00000246 ORIG_RAX: 000000000000013a
> RAX: ffffffffffffffda RBX: 00000000006e49f8 RCX: 000000000044c829
> RDX: 0000000000000000 RSI: 0000000020000000 RDI: 0000000000000000
> RBP: 00000000006e49f0 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 00000000006e49fc
> R13: 00007ffd1981c8af R14: 00007f28685e99c0 R15: 0000000000000001
> Shutting down cpus with NMI
> Kernel Offset: disabled
> Rebooting in 86400 seconds..
>