Re: [syzbot] WARNING: suspicious RCU usage in kernfs_iop_getattr

[Dmitry Vyukov]

On Mon, May 3, 2021 at 6:30 AM syzbot
<syzbot+c26b2cb5301be7de9efc@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
>
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit:    d72cd4ad Merge tag 'scsi-misc' of git://git.kernel.org/pub..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=123fbb85d00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=53fdf14defd48c56
> dashboard link: https://syzkaller.appspot.com/bug?extid=c26b2cb5301be7de9efc
> compiler:       Debian clang version 11.0.1-2
>
> 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+c26b2cb5301be7de9efc@xxxxxxxxxxxxxxxxxxxxxxxxx

#syz fix: rcu: Reject RCU_LOCKDEP_WARN() false positives

> =============================
> 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 systemd-udevd/4826.
>
> stack backtrace:
> CPU: 1 PID: 4826 Comm: systemd-udevd 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+0x202/0x31e lib/dump_stack.c:120
>  ___might_sleep+0x114/0x6b0 kernel/sched/core.c:8304
>  __mutex_lock_common+0xce/0x2e50 kernel/locking/mutex.c:928
>  __mutex_lock kernel/locking/mutex.c:1096 [inline]
>  mutex_lock_nested+0x1a/0x20 kernel/locking/mutex.c:1111
>  kernfs_iop_getattr+0x89/0x310 fs/kernfs/inode.c:194
>  vfs_getattr fs/stat.c:134 [inline]
>  vfs_statx+0x1ba/0x3d0 fs/stat.c:199
>  vfs_fstatat fs/stat.c:217 [inline]
>  vfs_lstat include/linux/fs.h:3384 [inline]
>  __do_sys_newlstat fs/stat.c:372 [inline]
>  __se_sys_newlstat fs/stat.c:366 [inline]
>  __x64_sys_newlstat+0xd3/0x150 fs/stat.c:366
>  do_syscall_64+0x3f/0xb0 arch/x86/entry/common.c:47
>  entry_SYSCALL_64_after_hwframe+0x44/0xae
> RIP: 0033:0x7f41b6750335
> Code: 69 db 2b 00 64 c7 00 16 00 00 00 b8 ff ff ff ff c3 0f 1f 40 00 83 ff 01 48 89 f0 77 30 48 89 c7 48 89 d6 b8 06 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 03 f3 c3 90 48 8b 15 31 db 2b 00 f7 d8 64 89
> RSP: 002b:00007ffe4d8d3b08 EFLAGS: 00000246
>  ORIG_RAX: 0000000000000006
> RAX: ffffffffffffffda RBX: 00005601243f1120 RCX: 00007f41b6750335
> RDX: 00007ffe4d8d3b40 RSI: 00007ffe4d8d3b40 RDI: 00005601243f0120
> RBP: 00007ffe4d8d3c00 R08: 00007f41b6a0f228 R09: 0000000000001010
> R10: 00007f41b6a0eb58 R11: 0000000000000246 R12: 00005601243f0120
> R13: 00005601243f0134 R14: 000056012440253d R15: 0000560124402544
>
>
> ---
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