Hello,
syzbot found the following issue on:
HEAD commit: d2b6f8a1 Merge tag 'xfs-5.13-merge-3' of git://git.kernel...
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=123a56a5d00000
kernel config: https://syzkaller.appspot.com/x/.config?x=65c207250bba4efe
dashboard link: https://syzkaller.appspot.com/bug?extid=37fc8b84ffa2279d636d
userspace arch: i386
Unfortunately, I don't have any reproducer for this issue yet.
IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: [email protected]
=============================
WARNING: suspicious RCU usage
5.12.0-syzkaller #0 Not tainted
-----------------------------
kernel/sched/core.c:8304 Illegal context switch in RCU-sched read-side critical section!
other info that might help us debug this:
rcu_scheduler_active = 2, debug_locks = 0
no locks held by syz-executor.4/10430.
stack backtrace:
CPU: 0 PID: 10430 Comm: syz-executor.4 Not tainted 5.12.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:79 [inline]
dump_stack+0x141/0x1d7 lib/dump_stack.c:120
___might_sleep+0x266/0x2c0 kernel/sched/core.c:8304
try_to_freeze_unsafe include/linux/freezer.h:57 [inline]
try_to_freeze include/linux/freezer.h:67 [inline]
get_signal+0x14a/0x2150 kernel/signal.c:2613
arch_do_signal_or_restart+0x2a8/0x1eb0 arch/x86/kernel/signal.c:789
handle_signal_work kernel/entry/common.c:147 [inline]
exit_to_user_mode_loop kernel/entry/common.c:171 [inline]
exit_to_user_mode_prepare+0x171/0x280 kernel/entry/common.c:208
irqentry_exit_to_user_mode+0x5/0x40 kernel/entry/common.c:314
exc_page_fault+0xc6/0x180 arch/x86/mm/fault.c:1534
asm_exc_page_fault+0x1e/0x30 arch/x86/include/asm/idtentry.h:577
RIP: 0023:0x8052207
Code: 0c 50 e8 ac 5a 01 00 83 c4 10 85 c0 0f 84 b9 01 00 00 65 f0 83 2d d8 ff ff ff 01 8b 5c 24 08 e8 6f f7 00 00 8b 4c 24 0c 8b 00 <8b> 71 50 89 41 54 85 c0 75 05 83 fe ff 74 19 6b 44 24 1c 34 8b 4c
RSP: 002b:00000000f5514640 EFLAGS: 00010283
RAX: 000000000000000e RBX: 0000000000000000 RCX: 0000000000000000
RDX: 00000000080521e4 RSI: 0000000000000005 RDI: 00000000080ea51d
RBP: 000000000819afc0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000296 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
---
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On Fri, May 7, 2021 at 10:38 AM Peter Zijlstra <[email protected]> wrote:
>
> On Thu, May 06, 2021 at 02:34:27PM -0700, syzbot wrote:
> > Hello,
> >
> > syzbot found the following issue on:
> >
> > HEAD commit: d2b6f8a1 Merge tag 'xfs-5.13-merge-3' of git://git.kernel...
> > git tree: upstream
> > console output: https://syzkaller.appspot.com/x/log.txt?x=123a56a5d00000
> > kernel config: https://syzkaller.appspot.com/x/.config?x=65c207250bba4efe
> > dashboard link: https://syzkaller.appspot.com/bug?extid=37fc8b84ffa2279d636d
> > userspace arch: i386
> >
> > Unfortunately, I don't have any reproducer for this issue yet.
> >
> > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > Reported-by: [email protected]
> >
> > =============================
> > WARNING: suspicious RCU usage
> > 5.12.0-syzkaller #0 Not tainted
> > -----------------------------
> > kernel/sched/core.c:8304 Illegal context switch in RCU-sched read-side critical section!
> >
> > other info that might help us debug this:
> >
> >
> > rcu_scheduler_active = 2, debug_locks = 0
> > no locks held by syz-executor.4/10430.
>
> Looks like this is a concurrent fail?, if !debug_locks (as per the above)
> then RCU_LOCKDEP_WARN() should not trigger.
FTR the log is here:
https://syzkaller.appspot.com/text?tag=CrashLog&x=123a56a5d00000
It contains 2 intermixed reports:
[ 289.896033][T10430] =============================
[ 289.896039][T10430] WARNING: suspicious RCU usage
[ 289.896046][T10430] 5.12.0-syzkaller #0 Not tainted
[ 289.898388][T13493] ======================================================
[ 289.898401][T13493] WARNING: possible circular locking dependency detected
[ 289.898410][T13493] 5.12.0-syzkaller #0 Not tainted
[ 289.898424][T13493] ------------------------------------------------------
[ 289.898432][T13493] syz-executor.0/13493 is trying to acquire lock:
[ 289.898448][T13493] ffff888019065ca0 (&bdev->bd_mutex){+.+.}-{3:3},
at: del_gendisk+0x250/0x9e0
On Thu, May 06, 2021 at 02:34:27PM -0700, syzbot wrote:
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit: d2b6f8a1 Merge tag 'xfs-5.13-merge-3' of git://git.kernel...
> git tree: upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=123a56a5d00000
> kernel config: https://syzkaller.appspot.com/x/.config?x=65c207250bba4efe
> dashboard link: https://syzkaller.appspot.com/bug?extid=37fc8b84ffa2279d636d
> userspace arch: i386
>
> Unfortunately, I don't have any reproducer for this issue yet.
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: [email protected]
>
> =============================
> WARNING: suspicious RCU usage
> 5.12.0-syzkaller #0 Not tainted
> -----------------------------
> kernel/sched/core.c:8304 Illegal context switch in RCU-sched read-side critical section!
>
> other info that might help us debug this:
>
>
> rcu_scheduler_active = 2, debug_locks = 0
> no locks held by syz-executor.4/10430.
Looks like this is a concurrent fail?, if !debug_locks (as per the above)
then RCU_LOCKDEP_WARN() should not trigger.
On Fri, May 07, 2021 at 10:42:48AM +0200, Dmitry Vyukov wrote:
> On Fri, May 7, 2021 at 10:38 AM Peter Zijlstra <[email protected]> wrote:
> >
> > On Thu, May 06, 2021 at 02:34:27PM -0700, syzbot wrote:
> > > Hello,
> > >
> > > syzbot found the following issue on:
> > >
> > > HEAD commit: d2b6f8a1 Merge tag 'xfs-5.13-merge-3' of git://git.kernel...
> > > git tree: upstream
> > > console output: https://syzkaller.appspot.com/x/log.txt?x=123a56a5d00000
> > > kernel config: https://syzkaller.appspot.com/x/.config?x=65c207250bba4efe
> > > dashboard link: https://syzkaller.appspot.com/bug?extid=37fc8b84ffa2279d636d
> > > userspace arch: i386
> > >
> > > Unfortunately, I don't have any reproducer for this issue yet.
> > >
> > > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > > Reported-by: [email protected]
> > >
> > > =============================
> > > WARNING: suspicious RCU usage
> > > 5.12.0-syzkaller #0 Not tainted
> > > -----------------------------
> > > kernel/sched/core.c:8304 Illegal context switch in RCU-sched read-side critical section!
> > >
> > > other info that might help us debug this:
> > >
> > >
> > > rcu_scheduler_active = 2, debug_locks = 0
> > > no locks held by syz-executor.4/10430.
> >
> > Looks like this is a concurrent fail?, if !debug_locks (as per the above)
> > then RCU_LOCKDEP_WARN() should not trigger.
>
> FTR the log is here:
> https://syzkaller.appspot.com/text?tag=CrashLog&x=123a56a5d00000
>
> It contains 2 intermixed reports:
>
> [ 289.896033][T10430] =============================
> [ 289.896039][T10430] WARNING: suspicious RCU usage
> [ 289.896046][T10430] 5.12.0-syzkaller #0 Not tainted
> [ 289.898388][T13493] ======================================================
> [ 289.898401][T13493] WARNING: possible circular locking dependency detected
> [ 289.898410][T13493] 5.12.0-syzkaller #0 Not tainted
> [ 289.898424][T13493] ------------------------------------------------------
> [ 289.898432][T13493] syz-executor.0/13493 is trying to acquire lock:
> [ 289.898448][T13493] ffff888019065ca0 (&bdev->bd_mutex){+.+.}-{3:3},
> at: del_gendisk+0x250/0x9e0
This "suspicious RCU usage" false positive looks to be addressed by this
commit in -rcu, slated for the v5.14 merge window:
81a5e05455d4 ("rcu: Reject RCU_LOCKDEP_WARN() false positives")
So I suggest ignoring the "suspicious RCU usage" report in favor of the
"possible circular locking dependency detected" report.
Thanx, Paul
On Fri, May 7, 2021 at 7:19 PM Paul E. McKenney <[email protected]> wrote:
>
> On Fri, May 07, 2021 at 10:42:48AM +0200, Dmitry Vyukov wrote:
> > On Fri, May 7, 2021 at 10:38 AM Peter Zijlstra <[email protected]> wrote:
> > >
> > > On Thu, May 06, 2021 at 02:34:27PM -0700, syzbot wrote:
> > > > Hello,
> > > >
> > > > syzbot found the following issue on:
> > > >
> > > > HEAD commit: d2b6f8a1 Merge tag 'xfs-5.13-merge-3' of git://git.kernel...
> > > > git tree: upstream
> > > > console output: https://syzkaller.appspot.com/x/log.txt?x=123a56a5d00000
> > > > kernel config: https://syzkaller.appspot.com/x/.config?x=65c207250bba4efe
> > > > dashboard link: https://syzkaller.appspot.com/bug?extid=37fc8b84ffa2279d636d
> > > > userspace arch: i386
> > > >
> > > > Unfortunately, I don't have any reproducer for this issue yet.
> > > >
> > > > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > > > Reported-by: [email protected]
> > > >
> > > > =============================
> > > > WARNING: suspicious RCU usage
> > > > 5.12.0-syzkaller #0 Not tainted
> > > > -----------------------------
> > > > kernel/sched/core.c:8304 Illegal context switch in RCU-sched read-side critical section!
> > > >
> > > > other info that might help us debug this:
> > > >
> > > >
> > > > rcu_scheduler_active = 2, debug_locks = 0
> > > > no locks held by syz-executor.4/10430.
> > >
> > > Looks like this is a concurrent fail?, if !debug_locks (as per the above)
> > > then RCU_LOCKDEP_WARN() should not trigger.
> >
> > FTR the log is here:
> > https://syzkaller.appspot.com/text?tag=CrashLog&x=123a56a5d00000
> >
> > It contains 2 intermixed reports:
> >
> > [ 289.896033][T10430] =============================
> > [ 289.896039][T10430] WARNING: suspicious RCU usage
> > [ 289.896046][T10430] 5.12.0-syzkaller #0 Not tainted
> > [ 289.898388][T13493] ======================================================
> > [ 289.898401][T13493] WARNING: possible circular locking dependency detected
> > [ 289.898410][T13493] 5.12.0-syzkaller #0 Not tainted
> > [ 289.898424][T13493] ------------------------------------------------------
> > [ 289.898432][T13493] syz-executor.0/13493 is trying to acquire lock:
> > [ 289.898448][T13493] ffff888019065ca0 (&bdev->bd_mutex){+.+.}-{3:3},
> > at: del_gendisk+0x250/0x9e0
>
> This "suspicious RCU usage" false positive looks to be addressed by this
> commit in -rcu, slated for the v5.14 merge window:
>
> 81a5e05455d4 ("rcu: Reject RCU_LOCKDEP_WARN() false positives")
>
> So I suggest ignoring the "suspicious RCU usage" report in favor of the
> "possible circular locking dependency detected" report.
Oh, I see, it's not merged yet.
In my memory we discussed it so long ago that I assumed it is fixed already.
Let's mark it as fixed then:
#syz fix: rcu: Reject RCU_LOCKDEP_WARN() false positives
Thanks for double checking.
On Sat, May 08, 2021 at 07:03:51AM +0200, Dmitry Vyukov wrote:
> On Fri, May 7, 2021 at 7:19 PM Paul E. McKenney <[email protected]> wrote:
> >
> > On Fri, May 07, 2021 at 10:42:48AM +0200, Dmitry Vyukov wrote:
> > > On Fri, May 7, 2021 at 10:38 AM Peter Zijlstra <[email protected]> wrote:
> > > >
> > > > On Thu, May 06, 2021 at 02:34:27PM -0700, syzbot wrote:
> > > > > Hello,
> > > > >
> > > > > syzbot found the following issue on:
> > > > >
> > > > > HEAD commit: d2b6f8a1 Merge tag 'xfs-5.13-merge-3' of git://git.kernel...
> > > > > git tree: upstream
> > > > > console output: https://syzkaller.appspot.com/x/log.txt?x=123a56a5d00000
> > > > > kernel config: https://syzkaller.appspot.com/x/.config?x=65c207250bba4efe
> > > > > dashboard link: https://syzkaller.appspot.com/bug?extid=37fc8b84ffa2279d636d
> > > > > userspace arch: i386
> > > > >
> > > > > Unfortunately, I don't have any reproducer for this issue yet.
> > > > >
> > > > > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > > > > Reported-by: [email protected]
> > > > >
> > > > > =============================
> > > > > WARNING: suspicious RCU usage
> > > > > 5.12.0-syzkaller #0 Not tainted
> > > > > -----------------------------
> > > > > kernel/sched/core.c:8304 Illegal context switch in RCU-sched read-side critical section!
> > > > >
> > > > > other info that might help us debug this:
> > > > >
> > > > >
> > > > > rcu_scheduler_active = 2, debug_locks = 0
> > > > > no locks held by syz-executor.4/10430.
> > > >
> > > > Looks like this is a concurrent fail?, if !debug_locks (as per the above)
> > > > then RCU_LOCKDEP_WARN() should not trigger.
> > >
> > > FTR the log is here:
> > > https://syzkaller.appspot.com/text?tag=CrashLog&x=123a56a5d00000
> > >
> > > It contains 2 intermixed reports:
> > >
> > > [ 289.896033][T10430] =============================
> > > [ 289.896039][T10430] WARNING: suspicious RCU usage
> > > [ 289.896046][T10430] 5.12.0-syzkaller #0 Not tainted
> > > [ 289.898388][T13493] ======================================================
> > > [ 289.898401][T13493] WARNING: possible circular locking dependency detected
> > > [ 289.898410][T13493] 5.12.0-syzkaller #0 Not tainted
> > > [ 289.898424][T13493] ------------------------------------------------------
> > > [ 289.898432][T13493] syz-executor.0/13493 is trying to acquire lock:
> > > [ 289.898448][T13493] ffff888019065ca0 (&bdev->bd_mutex){+.+.}-{3:3},
> > > at: del_gendisk+0x250/0x9e0
> >
> > This "suspicious RCU usage" false positive looks to be addressed by this
> > commit in -rcu, slated for the v5.14 merge window:
> >
> > 81a5e05455d4 ("rcu: Reject RCU_LOCKDEP_WARN() false positives")
> >
> > So I suggest ignoring the "suspicious RCU usage" report in favor of the
> > "possible circular locking dependency detected" report.
>
> Oh, I see, it's not merged yet.
> In my memory we discussed it so long ago that I assumed it is fixed already.
It was a bit too late to make my pull request. I won't lose it. ;-)
Thanx, Paul
> Let's mark it as fixed then:
>
> #syz fix: rcu: Reject RCU_LOCKDEP_WARN() false positives
>
> Thanks for double checking.