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Subject: Re: [syzbot] WARNING in exit_tasks_rcu_finish

On Mon, Jun 13, 2022 at 11:54:45PM +0000, Zhang, Qiang1 wrote:
> On Mon, Jun 13, 2022 at 10:26:47PM +0000, Zhang, Qiang1 wrote:
> > On Mon, Jun 13, 2022 at 01:55:31PM +0000, Zhang, Qiang1 wrote:
> > > > syzbot <[email protected]> writes:
> > > >
> > > > > Hello,
> > > > >
> > > > > syzbot found the following issue on:
> > > > >
> > > > > HEAD commit: 6d0c80680317 Add linux-next specific files for 20220610
> > > > > git tree: linux-next
> > > > > console output:
> > > > > https://syzkaller.appspot.com/x/log.txt?x=13b52c2ff00000
> > > > > kernel config:
> > > > > https://syzkaller.appspot.com/x/.config?x=a30d6e3e814e5931
> > > > > dashboard link: https://syzkaller.appspot.com/bug?extid=9bb26e7c5e8e4fa7e641
> > > > > compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
> > > > >
> > > > > Unfortunately, I don't have any reproducer for this issue yet.
> > > >
> > > > I don't understand what is going on in linux-next
> > > > kernel/rcu/tasks.h looks different than in Linus's tree. Paul
> > > > does that mean you have some staged rcu changes?
> > >
> > > >Less than 100 RCU-related patches in -rcu, so not all that bad.
> > > >;-)
> > > >
> > > >But yes, this could possibly be an issue in one of those patches.
> > >
> > > > Eric
> > > >
> > > >
> > > > > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > > > > Reported-by:
> > > > > [email protected]
> > > > >
> > > > > ------------[ cut here ]------------
> > > > > WARNING: CPU: 1 PID: 28639 at kernel/rcu/tasks.h:1664
> > > > > exit_tasks_rcu_finish_trace kernel/rcu/tasks.h:1664 [inline]
> > > > > WARNING: CPU: 1 PID: 28639 at kernel/rcu/tasks.h:1664
> > > > > exit_tasks_rcu_finish+0x122/0x1b0 kernel/rcu/tasks.h:1006
> > >
> > > >The usual way for this warning to trigger is for these a task to exit while in an RCU Tasks Trace read-side critical section:
> > > >
> > > > rcu_read_lock_trace();
> > > > do_something_that_causes_task_exit();
> > > >
> > >
> > > Hi Paul, wether the following scenarios be considered
> > >
> > > rcu_read_unlock_trace_special
> > > ->if (trs.b.blocked)
> > > ->raw_spin_lock_irqsave_rcu_node
> > > ->list_del_init(&t->trc_blkd_node)
> > > ->WRITE_ONCE(t->trc_reader_special.b.blocked, false)
> > > ->raw_spin_unlock_irqrestore_rcu_node
> > > ->Inerrrupt
> > > ->schedule
> > > ->rcu_note_context_switch
> > > ->rcu_tasks_trace_qs
> > > If (___rttq_nesting && !READ_ONCE((t)->trc_reader_special.b.blocked)
> > > /*___rttq_nesting ==1 && (t)->trc_reader_special.b.blocked =false*/
> > > rcu_tasks_trace_qs_blkd(t)
> > > ->WRITE_ONCE(t->trc_reader_nesting, 0)
> > > .......
> > > -> exit_tasks_rcu_finish
> > >
> > > Whether the following patch can fix it, or what am I missing?
> > > Any thoughts?
> > >
> > > diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h index
> > > f1209ce621c5..c607e4c914d3 100644
> > > --- a/kernel/rcu/tasks.h
> > > +++ b/kernel/rcu/tasks.h
> > > @@ -1247,6 +1247,7 @@ void rcu_read_unlock_trace_special(struct task_struct *t)
> > > struct rcu_tasks_percpu *rtpcp;
> > > union rcu_special trs;
> > >
> > > + WRITE_ONCE(t->trc_reader_nesting, 0);
> > > // Open-coded full-word version of rcu_ld_need_qs().
> > > smp_mb(); // Enforce full grace-period ordering.
> > > trs = smp_load_acquire(&t->trc_reader_special);
> > > @@ -1267,7 +1268,6 @@ void rcu_read_unlock_trace_special(struct task_struct *t)
> > > WRITE_ONCE(t->trc_reader_special.b.blocked, false);
> > > raw_spin_unlock_irqrestore_rcu_node(rtpcp, flags);
> > > }
> > > - WRITE_ONCE(t->trc_reader_nesting, 0);
> > > }
> > > EXPORT_SYMBOL_GPL(rcu_read_unlock_trace_special);
> >
> > >Thank you for looking into this!
> > >
> > >You do have what I believe to be the correct failure scenario, but the above fix would break nested RCU Tasks Trace read-side critical sections.
> >
> > Hi Paul
> >
> > Break nested RCU Tasks Trace read-side critical sections?
> > Does it mean the following?
> >
> > rcu_read_unlock_trace
> > -> WRITE_ONCE(t->trc_reader_nesting, INT_MIN);
> > /* t->trc_reader_special.s == 0*/
> > -> if (likely(!READ_ONCE(t->trc_reader_special.s)) || nesting)
> > -> Interrupt
> > -> schedule
> > -> rcu_note_context_switch
> > -> rcu_tasks_trace_qs
> > /*___rttq_nesting == INT_MIN && (t)->trc_reader_special.b.blocked == false*/
> > ->rcu_tasks_trace_qs_blkd(t)
> > /*nesting == 0*/
> > -> WRITE_ONCE(t->trc_reader_nesting, nesting);
> > -> return;
> > .........
> > exit_tasks_rcu_finish
> > trigger Warnings
> >
> > Or where am I misunderstanding?
>
> >I suspect that you do in fact understand it. Let's walk through the failure scenario again and see.
> >
> >If that READ_ONCE(t->trc_reader_special.s) return zero as you suggest, and then the interrupt and schedule happen as you suggest, then
> >rcu_tasks_trace_qs_blkd() will see a non-zero ->trc_reader_nesting and a zero .b.blocked. It queues the task, but rcu_read_unlock_trace() won't check again. It will set ->trc_reader_nesting to zero and continue. As you noted, if the task exits in that state, then
> >exit_tasks_rcu_finish_trace() will trigger its WARN_ON_ONCE().
>
> I understand the problem you describe, Just like the call flow I described above,
> rcu_read_unlock_trace_special() may not be called.

Very good!

Thanx, Paul

> Thanks
> Zqiang
>
> >
> >Your change won't affect this because rcu_read_unlock_trace_special() never gets called.
> >
> >Hence the approach in the patch below.
> >
> >Do you see any failure modes given the below patch?
>
> > Thanks
> > Zqiang
> >
> > >
> > >But would you be willing to try out the patch shown below?
> >
> > I will try to test it.
>
> >Thank you very much!
> >
> > Thanx, Paul
>
> > >---------------------------------------------------------------------
> > >---
> >
> > diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index
> > 08059d8d4f5a7..937a58b3266bf 100644
> > --- a/include/linux/rcupdate.h
> > +++ b/include/linux/rcupdate.h
> > @@ -184,7 +184,7 @@ void rcu_tasks_trace_qs_blkd(struct task_struct *t);
> > if (likely(!READ_ONCE((t)->trc_reader_special.b.need_qs)) && \
> > likely(!___rttq_nesting)) { \
> > rcu_trc_cmpxchg_need_qs((t), 0, TRC_NEED_QS_CHECKED); \
> > - } else if (___rttq_nesting && \
> > + } else if (___rttq_nesting && ___rttq_nesting != INT_MIN && \
> > !READ_ONCE((t)->trc_reader_special.b.blocked)) { \
> > rcu_tasks_trace_qs_blkd(t); \
> > } \
> > diff --git a/include/linux/rcupdate_trace.h
> > b/include/linux/rcupdate_trace.h index 6f9c358173989..9bc8cbb33340b
> > 100644
> > --- a/include/linux/rcupdate_trace.h
> > +++ b/include/linux/rcupdate_trace.h
> > @@ -75,7 +75,7 @@ static inline void rcu_read_unlock_trace(void)
> > nesting = READ_ONCE(t->trc_reader_nesting) - 1;
> > barrier(); // Critical section before disabling.
> > // Disable IPI-based setting of .need_qs.
> > - WRITE_ONCE(t->trc_reader_nesting, INT_MIN);
> > + WRITE_ONCE(t->trc_reader_nesting, INT_MIN + nesting);
> > if (likely(!READ_ONCE(t->trc_reader_special.s)) || nesting) {
> > WRITE_ONCE(t->trc_reader_nesting, nesting);
> > return; // We assume shallow reader nesting.

2022-06-14 01:03:59

by Zqiang

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Subject: RE: [syzbot] WARNING in exit_tasks_rcu_finish

On Mon, Jun 13, 2022 at 04:42:07PM -0700, Kees Cook wrote:
> On Mon, Jun 13, 2022 at 10:36:07AM -0700, syzbot wrote:
> > Hello,
> >
> > syzbot has tested the proposed patch and the reproducer did not trigger any issue:
> >
> > Reported-and-tested-by:
> > [email protected]
>
> Looks like the patch solved the reproducer. :)

>For one of the two possible ways to make the bug happen. ;-)
>
>Still, good on Qiang for identifying one of the paths! Not just anyone can do that.

Thanks Paul, yes this patch can solved the reproducer and I also test it.

I compiled "bpf_test" according to the c file in the following link

C reproducer: https://syzkaller.appspot.com/x/repro.c?x=148207bff00000

Not apply this patch, this calltrace reproduce

root@qemux86-64:/# ./bpf_test
^C
root@qemux86-64:/# dmesg
[ 147.017232] ------------[ cut here ]------------
[ 147.017234] WARNING: CPU: 3 PID: 21586 at kernel/rcu/tasks.h:1664 exit_tasks_rcu_finish+0xbf/0x100
[ 147.017245] Modules linked in:
[ 147.017249] CPU: 3 PID: 21586 Comm: bpf_test Not tainted 5.19.0-rc1-next-20220610-yoctodev-standard #204
[ 147.017253] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.16.0-0-gd239552ce722-prebuilt.qemu.org 04/01/2014
[ 147.017256] RIP: 0010:exit_tasks_rcu_finish+0xbf/0x100
[ 147.017261] Code: 03 00 00 85 c0 75 59 f0 83 44 24 fc 00 49 8d bc 24 41 03 00 00 e8 21 09 2b 00 41 0f b6 84 24 41 03 00 00 83 e0 01 08 d8 74 11 <0f> 8
[ 147.017264] RSP: 0018:ffff88810ccd7af0 EFLAGS: 00010202
[ 147.017268] RAX: 0000000000000001 RBX: 0000000000000201 RCX: ffffffff897ab52f
[ 147.017271] RDX: 1ffff1102181d7c8 RSI: 0000000000000000 RDI: ffff88810c0ebe41
[ 147.017274] RBP: ffff88810ccd7b08 R08: ffffffff897ab510 R09: 0000000000000000
[ 147.017277] R10: ffffffff8c407bbf R11: 0000000000000000 R12: ffff88810c0ebb00
[ 147.017279] R13: ffff88810c0ebe38 R14: ffff88810ccd7b78 R15: ffff88810ccd76b0
[ 147.017282] FS: 0000000000000000(0000) GS:ffff88815a000000(0000) knlGS:0000000000000000
[ 147.017287] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 147.017289] CR2: 0000000000000000 CR3: 000000011ac16000 CR4: 00000000001506e0
[ 147.017292] Call Trace:
[ 147.017294] <TASK>
[ 147.017297] do_exit+0xe9a/0x13a0
[ 147.017305] ? mm_update_next_owner+0x450/0x450
[ 147.017309] ? lock_downgrade+0x410/0x410
[ 147.017313] ? lock_contended+0x790/0x790
[ 147.017317] ? rcu_read_lock_held_common+0x1e/0x60
[ 147.017324] do_group_exit+0x71/0x150
[ 147.017329] get_signal+0x1319/0x1340
[ 147.017334] ? futex_wait_setup+0x180/0x180
[ 147.017341] ? exit_signals+0x4c0/0x4c0
[ 147.017345] ? futex_wake+0x29e/0x2e0
[ 147.017351] arch_do_signal_or_restart+0x9c/0xc60
[ 147.017357] ? rcu_read_lock_sched_held+0x60/0xd0
[ 147.017361] ? rcu_read_lock_bh_held+0xb0/0xb0
[ 147.017367] ? get_sigframe_size+0x20/0x20
[ 147.017371] ? do_futex+0x1a2/0x240
[ 147.017375] ? __ia32_sys_get_robust_list+0x240/0x240
[ 147.017378] ? __context_tracking_exit+0x91/0xa0
[ 147.017385] ? lock_downgrade+0x410/0x410
[ 147.017390] ? __x64_sys_futex+0x125/0x2b0
[ 147.017393] ? rcu_read_lock_held_common+0x1e/0x60
[ 147.017399] ? lockdep_hardirqs_on_prepare+0x13/0x230
[ 147.017403] ? exit_to_user_mode_prepare+0x151/0x240
[ 147.017409] exit_to_user_mode_prepare+0x16c/0x240
[ 147.017415] syscall_exit_to_user_mode+0x1e/0x70
[ 147.017419] do_syscall_64+0x50/0x90
[ 147.017423] entry_SYSCALL_64_after_hwframe+0x46/0xb0
[ 147.017427] RIP: 0033:0x7f780e668fbd
[ 147.017431] Code: Unable to access opcode bytes at RIP 0x7f780e668f93.
[ 147.017433] RSP: 002b:00007f780e55bd48 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
[ 147.017437] RAX: fffffffffffffe00 RBX: 00007f780e55c640 RCX: 00007f780e668fbd
[ 147.017440] RDX: 0000000000000000 RSI: 0000000000000080 RDI: 000055ed9f3a8088
[ 147.017442] RBP: 00007f780e55bd60 R08: 0000000100000001 R09: 0000000100000001
[ 147.017445] R10: 0000000000000000 R11: 0000000000000246 R12: fffffffffffffeb0
[ 147.017447] R13: 0000000000000000 R14: 00007ffe5dcf20a0 R15: 00007f780e53c000
[ 147.017455] </TASK>
[ 147.017458] irq event stamp: 0
[ 147.017460] hardirqs last enabled at (0): [<0000000000000000>] 0x0
[ 147.017463] hardirqs last disabled at (0): [<ffffffff896b5990>] copy_process+0xe30/0x35f0
[ 147.017467] softirqs last enabled at (0): [<ffffffff896b5990>] copy_process+0xe30/0x35f0
[ 147.017470] softirqs last disabled at (0): [<0000000000000000>] 0x0
[ 147.017473] ---[ end trace 0000000000000000 ]---

Apply this patch , this problem not reproduce.

Thanks
Zqiang

>
> Thanx, Paul
>
> > Tested on:
> >
> > commit: 6d0c8068 Add linux-next specific files for 20220610
> > git tree: git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git next-20220610
> > console output:
> > https://syzkaller.appspot.com/x/log.txt?x=12d068eff00000
> > kernel config:
> > https://syzkaller.appspot.com/x/.config?x=a30d6e3e814e5931
> > dashboard link: https://syzkaller.appspot.com/bug?extid=9bb26e7c5e8e4fa7e641
> > compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
> > patch: https://syzkaller.appspot.com/x/patch.diff?x=147f47c8080000
> >
> > Note: testing is done by a robot and is best-effort only.
>
> You can see the dashboard link above for testing details...
>
> --
> Kees Cook

2022-06-14 03:07:20

by Zqiang

[permalink] [raw]

Subject: RE: [syzbot] WARNING in exit_tasks_rcu_finish

On Tue, Jun 14, 2022 at 12:52:23AM +0000, Zhang, Qiang1 wrote:
> On Mon, Jun 13, 2022 at 04:42:07PM -0700, Kees Cook wrote:
> > On Mon, Jun 13, 2022 at 10:36:07AM -0700, syzbot wrote:
> > > Hello,
> > >
> > > syzbot has tested the proposed patch and the reproducer did not trigger any issue:
> > >
> > > Reported-and-tested-by:
> > > [email protected]
> >
> > Looks like the patch solved the reproducer. :)
>
> >For one of the two possible ways to make the bug happen. ;-)
> >
> >Still, good on Qiang for identifying one of the paths! Not just anyone can do that.
>
> Thanks Paul, yes this patch can solved the reproducer and I also test it.
>
> I compiled "bpf_test" according to the c file in the following link
>
> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=148207bff00000
>
> Not apply this patch, this calltrace reproduce
>
> root@qemux86-64:/# ./bpf_test
> ^C
> root@qemux86-64:/# dmesg
> [ 147.017232] ------------[ cut here ]------------ [ 147.017234]
> WARNING: CPU: 3 PID: 21586 at kernel/rcu/tasks.h:1664
> exit_tasks_rcu_finish+0xbf/0x100 [ 147.017245] Modules linked in:
> [ 147.017249] CPU: 3 PID: 21586 Comm: bpf_test Not tainted
> 5.19.0-rc1-next-20220610-yoctodev-standard #204 [ 147.017253]
> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS
> rel-1.16.0-0-gd239552ce722-prebuilt.qemu.org 04/01/2014 [ 147.017256]
> RIP: 0010:exit_tasks_rcu_finish+0xbf/0x100
> [ 147.017261] Code: 03 00 00 85 c0 75 59 f0 83 44 24 fc 00 49 8d bc
> 24 41 03 00 00 e8 21 09 2b 00 41 0f b6 84 24 41 03 00 00 83 e0 01 08
> d8 74 11 <0f> 8 [ 147.017264] RSP: 0018:ffff88810ccd7af0 EFLAGS:
> 00010202 [ 147.017268] RAX: 0000000000000001 RBX: 0000000000000201
> RCX: ffffffff897ab52f [ 147.017271] RDX: 1ffff1102181d7c8 RSI:
> 0000000000000000 RDI: ffff88810c0ebe41 [ 147.017274] RBP:
> ffff88810ccd7b08 R08: ffffffff897ab510 R09: 0000000000000000 [
> 147.017277] R10: ffffffff8c407bbf R11: 0000000000000000 R12:
> ffff88810c0ebb00 [ 147.017279] R13: ffff88810c0ebe38 R14:
> ffff88810ccd7b78 R15: ffff88810ccd76b0 [ 147.017282] FS:
> 0000000000000000(0000) GS:ffff88815a000000(0000) knlGS:0000000000000000 [ 147.017287] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 147.017289] CR2: 0000000000000000 CR3: 000000011ac16000 CR4: 00000000001506e0 [ 147.017292] Call Trace:
> [ 147.017294] <TASK>
> [ 147.017297] do_exit+0xe9a/0x13a0
> [ 147.017305] ? mm_update_next_owner+0x450/0x450 [ 147.017309] ?
> lock_downgrade+0x410/0x410 [ 147.017313] ?
> lock_contended+0x790/0x790 [ 147.017317] ?
> rcu_read_lock_held_common+0x1e/0x60
> [ 147.017324] do_group_exit+0x71/0x150 [ 147.017329]
> get_signal+0x1319/0x1340 [ 147.017334] ?
> futex_wait_setup+0x180/0x180 [ 147.017341] ?
> exit_signals+0x4c0/0x4c0 [ 147.017345] ? futex_wake+0x29e/0x2e0 [
> 147.017351] arch_do_signal_or_restart+0x9c/0xc60
> [ 147.017357] ? rcu_read_lock_sched_held+0x60/0xd0
> [ 147.017361] ? rcu_read_lock_bh_held+0xb0/0xb0 [ 147.017367] ?
> get_sigframe_size+0x20/0x20 [ 147.017371] ? do_futex+0x1a2/0x240 [
> 147.017375] ? __ia32_sys_get_robust_list+0x240/0x240
> [ 147.017378] ? __context_tracking_exit+0x91/0xa0 [ 147.017385] ?
> lock_downgrade+0x410/0x410 [ 147.017390] ?
> __x64_sys_futex+0x125/0x2b0 [ 147.017393] ?
> rcu_read_lock_held_common+0x1e/0x60
> [ 147.017399] ? lockdep_hardirqs_on_prepare+0x13/0x230
> [ 147.017403] ? exit_to_user_mode_prepare+0x151/0x240
> [ 147.017409] exit_to_user_mode_prepare+0x16c/0x240
> [ 147.017415] syscall_exit_to_user_mode+0x1e/0x70
> [ 147.017419] do_syscall_64+0x50/0x90 [ 147.017423]
> entry_SYSCALL_64_after_hwframe+0x46/0xb0
> [ 147.017427] RIP: 0033:0x7f780e668fbd [ 147.017431] Code: Unable to
> access opcode bytes at RIP 0x7f780e668f93.
> [ 147.017433] RSP: 002b:00007f780e55bd48 EFLAGS: 00000246 ORIG_RAX:
> 00000000000000ca [ 147.017437] RAX: fffffffffffffe00 RBX:
> 00007f780e55c640 RCX: 00007f780e668fbd [ 147.017440] RDX:
> 0000000000000000 RSI: 0000000000000080 RDI: 000055ed9f3a8088 [
> 147.017442] RBP: 00007f780e55bd60 R08: 0000000100000001 R09:
> 0000000100000001 [ 147.017445] R10: 0000000000000000 R11:
> 0000000000000246 R12: fffffffffffffeb0 [ 147.017447] R13:
> 0000000000000000 R14: 00007ffe5dcf20a0 R15: 00007f780e53c000 [
> 147.017455] </TASK> [ 147.017458] irq event stamp: 0 [ 147.017460]
> hardirqs last enabled at (0): [<0000000000000000>] 0x0 [ 147.017463]
> hardirqs last disabled at (0): [<ffffffff896b5990>]
> copy_process+0xe30/0x35f0 [ 147.017467] softirqs last enabled at
> (0): [<ffffffff896b5990>] copy_process+0xe30/0x35f0 [ 147.017470]
> softirqs last disabled at (0): [<0000000000000000>] 0x0 [ 147.017473]
> ---[ end trace 0000000000000000 ]---
>
> Apply this patch , this problem not reproduce.
>
>Thank you very much! May I apply your Tested-by?

Thanks, I am very willing

>
> Thanx, Paul

> Thanks
> Zqiang
>
> >
> > Thanx, Paul
> >
> > > Tested on:
> > >
> > > commit: 6d0c8068 Add linux-next specific files for 20220610
> > > git tree: git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git next-20220610
> > > console output:
> > > https://syzkaller.appspot.com/x/log.txt?x=12d068eff00000
> > > kernel config:
> > > https://syzkaller.appspot.com/x/.config?x=a30d6e3e814e5931
> > > dashboard link: https://syzkaller.appspot.com/bug?extid=9bb26e7c5e8e4fa7e641
> > > compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
> > > patch: https://syzkaller.appspot.com/x/patch.diff?x=147f47c8080000
> > >
> > > Note: testing is done by a robot and is best-effort only.
> >
> > You can see the dashboard link above for testing details...
> >
> > --
> > Kees Cook

2022-06-14 03:07:48

by Paul E. McKenney

[permalink] [raw]

Subject: Re: [syzbot] WARNING in exit_tasks_rcu_finish

On Tue, Jun 14, 2022 at 12:52:23AM +0000, Zhang, Qiang1 wrote:
> On Mon, Jun 13, 2022 at 04:42:07PM -0700, Kees Cook wrote:
> > On Mon, Jun 13, 2022 at 10:36:07AM -0700, syzbot wrote:
> > > Hello,
> > >
> > > syzbot has tested the proposed patch and the reproducer did not trigger any issue:
> > >
> > > Reported-and-tested-by:
> > > [email protected]
> >
> > Looks like the patch solved the reproducer. :)
>
> >For one of the two possible ways to make the bug happen. ;-)
> >
> >Still, good on Qiang for identifying one of the paths! Not just anyone can do that.
>
> Thanks Paul, yes this patch can solved the reproducer and I also test it.
>
> I compiled "bpf_test" according to the c file in the following link
>
> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=148207bff00000
>
> Not apply this patch, this calltrace reproduce
>
> root@qemux86-64:/# ./bpf_test
> ^C
> root@qemux86-64:/# dmesg
> [ 147.017232] ------------[ cut here ]------------
> [ 147.017234] WARNING: CPU: 3 PID: 21586 at kernel/rcu/tasks.h:1664 exit_tasks_rcu_finish+0xbf/0x100
> [ 147.017245] Modules linked in:
> [ 147.017249] CPU: 3 PID: 21586 Comm: bpf_test Not tainted 5.19.0-rc1-next-20220610-yoctodev-standard #204
> [ 147.017253] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.16.0-0-gd239552ce722-prebuilt.qemu.org 04/01/2014
> [ 147.017256] RIP: 0010:exit_tasks_rcu_finish+0xbf/0x100
> [ 147.017261] Code: 03 00 00 85 c0 75 59 f0 83 44 24 fc 00 49 8d bc 24 41 03 00 00 e8 21 09 2b 00 41 0f b6 84 24 41 03 00 00 83 e0 01 08 d8 74 11 <0f> 8
> [ 147.017264] RSP: 0018:ffff88810ccd7af0 EFLAGS: 00010202
> [ 147.017268] RAX: 0000000000000001 RBX: 0000000000000201 RCX: ffffffff897ab52f
> [ 147.017271] RDX: 1ffff1102181d7c8 RSI: 0000000000000000 RDI: ffff88810c0ebe41
> [ 147.017274] RBP: ffff88810ccd7b08 R08: ffffffff897ab510 R09: 0000000000000000
> [ 147.017277] R10: ffffffff8c407bbf R11: 0000000000000000 R12: ffff88810c0ebb00
> [ 147.017279] R13: ffff88810c0ebe38 R14: ffff88810ccd7b78 R15: ffff88810ccd76b0
> [ 147.017282] FS: 0000000000000000(0000) GS:ffff88815a000000(0000) knlGS:0000000000000000
> [ 147.017287] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [ 147.017289] CR2: 0000000000000000 CR3: 000000011ac16000 CR4: 00000000001506e0
> [ 147.017292] Call Trace:
> [ 147.017294] <TASK>
> [ 147.017297] do_exit+0xe9a/0x13a0
> [ 147.017305] ? mm_update_next_owner+0x450/0x450
> [ 147.017309] ? lock_downgrade+0x410/0x410
> [ 147.017313] ? lock_contended+0x790/0x790
> [ 147.017317] ? rcu_read_lock_held_common+0x1e/0x60
> [ 147.017324] do_group_exit+0x71/0x150
> [ 147.017329] get_signal+0x1319/0x1340
> [ 147.017334] ? futex_wait_setup+0x180/0x180
> [ 147.017341] ? exit_signals+0x4c0/0x4c0
> [ 147.017345] ? futex_wake+0x29e/0x2e0
> [ 147.017351] arch_do_signal_or_restart+0x9c/0xc60
> [ 147.017357] ? rcu_read_lock_sched_held+0x60/0xd0
> [ 147.017361] ? rcu_read_lock_bh_held+0xb0/0xb0
> [ 147.017367] ? get_sigframe_size+0x20/0x20
> [ 147.017371] ? do_futex+0x1a2/0x240
> [ 147.017375] ? __ia32_sys_get_robust_list+0x240/0x240
> [ 147.017378] ? __context_tracking_exit+0x91/0xa0
> [ 147.017385] ? lock_downgrade+0x410/0x410
> [ 147.017390] ? __x64_sys_futex+0x125/0x2b0
> [ 147.017393] ? rcu_read_lock_held_common+0x1e/0x60
> [ 147.017399] ? lockdep_hardirqs_on_prepare+0x13/0x230
> [ 147.017403] ? exit_to_user_mode_prepare+0x151/0x240
> [ 147.017409] exit_to_user_mode_prepare+0x16c/0x240
> [ 147.017415] syscall_exit_to_user_mode+0x1e/0x70
> [ 147.017419] do_syscall_64+0x50/0x90
> [ 147.017423] entry_SYSCALL_64_after_hwframe+0x46/0xb0
> [ 147.017427] RIP: 0033:0x7f780e668fbd
> [ 147.017431] Code: Unable to access opcode bytes at RIP 0x7f780e668f93.
> [ 147.017433] RSP: 002b:00007f780e55bd48 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
> [ 147.017437] RAX: fffffffffffffe00 RBX: 00007f780e55c640 RCX: 00007f780e668fbd
> [ 147.017440] RDX: 0000000000000000 RSI: 0000000000000080 RDI: 000055ed9f3a8088
> [ 147.017442] RBP: 00007f780e55bd60 R08: 0000000100000001 R09: 0000000100000001
> [ 147.017445] R10: 0000000000000000 R11: 0000000000000246 R12: fffffffffffffeb0
> [ 147.017447] R13: 0000000000000000 R14: 00007ffe5dcf20a0 R15: 00007f780e53c000
> [ 147.017455] </TASK>
> [ 147.017458] irq event stamp: 0
> [ 147.017460] hardirqs last enabled at (0): [<0000000000000000>] 0x0
> [ 147.017463] hardirqs last disabled at (0): [<ffffffff896b5990>] copy_process+0xe30/0x35f0
> [ 147.017467] softirqs last enabled at (0): [<ffffffff896b5990>] copy_process+0xe30/0x35f0
> [ 147.017470] softirqs last disabled at (0): [<0000000000000000>] 0x0
> [ 147.017473] ---[ end trace 0000000000000000 ]---
>
> Apply this patch , this problem not reproduce.

Thank you very much! May I apply your Tested-by?

Thanx, Paul

> Thanks
> Zqiang
>
> >
> > Thanx, Paul
> >
> > > Tested on:
> > >
> > > commit: 6d0c8068 Add linux-next specific files for 20220610
> > > git tree: git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git next-20220610
> > > console output:
> > > https://syzkaller.appspot.com/x/log.txt?x=12d068eff00000
> > > kernel config:
> > > https://syzkaller.appspot.com/x/.config?x=a30d6e3e814e5931
> > > dashboard link: https://syzkaller.appspot.com/bug?extid=9bb26e7c5e8e4fa7e641
> > > compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
> > > patch: https://syzkaller.appspot.com/x/patch.diff?x=147f47c8080000
> > >
> > > Note: testing is done by a robot and is best-effort only.
> >
> > You can see the dashboard link above for testing details...
> >
> > --
> > Kees Cook