[syzbot] WARNING: suspicious RCU usage in __schedule

[Dmitry Vyukov]

On Sat, Apr 3, 2021 at 10:12 AM syzbot
<syzbot+be81a058b10931003a4a at syzkaller.appspotmail.com> wrote:
>
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit:    1e43c377 Merge tag 'xtensa-20210329' of git://github.com/j..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=1432bd1ad00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=78a83786814e7724
> dashboard link: https://syzkaller.appspot.com/bug?extid=be81a058b10931003a4a
> userspace arch: arm
>
> 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: syzbot+be81a058b10931003a4a at syzkaller.appspotmail.com

#syz dup: WARNING: suspicious RCU usage in getname_flags

> =============================
> WARNING: suspicious RCU usage
> 5.12.0-rc5-syzkaller-00003-g1e43c377a79f #0 Not tainted
> -----------------------------
> kernel/sched/core.c:4841 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 migration/1/17.
>
> stack backtrace:
> CPU: 1 PID: 17 Comm: migration/1 Not tainted 5.12.0-rc5-syzkaller-00003-g1e43c377a79f #0
> Hardware name: linux,dummy-virt (DT)
> Stopper: 0x0 <- 0x0
> Call trace:
>  dump_backtrace+0x0/0x3e0 arch/arm64/include/asm/pointer_auth.h:76
>  show_stack+0x18/0x24 arch/arm64/kernel/stacktrace.c:191
>  __dump_stack lib/dump_stack.c:79 [inline]
>  dump_stack+0x120/0x1a8 lib/dump_stack.c:120
>  lockdep_rcu_suspicious+0x130/0x148 kernel/locking/lockdep.c:6428
>  schedule_debug kernel/sched/core.c:4841 [inline]
>  __schedule+0x1244/0x1bc4 kernel/sched/core.c:4967
>  schedule+0xac/0x22c kernel/sched/core.c:5152
>  smpboot_thread_fn+0x278/0x7f4 kernel/smpboot.c:161
>  kthread+0x320/0x3bc kernel/kthread.c:292
>  ret_from_fork+0x10/0x3c arch/arm64/kernel/entry.S:958
>
>
> ---
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>
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