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

[Matthew Wilcox]

#syz dup: WARNING: suspicious RCU usage in getname_flags

On Fri, Apr 02, 2021 at 07:52:17PM -0700, syzbot 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=16d76301d00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=78ef1d159159890
> dashboard link: https://syzkaller.appspot.com/bug?extid=bdef67a6b28a89e6fe71
> 
> 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+bdef67a6b28a89e6fe71@xxxxxxxxxxxxxxxxxxxxxxxxx
> 
> =============================
> WARNING: suspicious RCU usage
> 5.12.0-rc5-syzkaller #0 Not tainted
> -----------------------------
> kernel/sched/core.c:8294 Illegal context switch in RCU-bh 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/4825.
> 
> stack backtrace:
> CPU: 1 PID: 4825 Comm: systemd-udevd Not tainted 5.12.0-rc5-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+0x229/0x2c0 kernel/sched/core.c:8294
>  dput+0x4d/0xbc0 fs/dcache.c:870
>  step_into+0x2cf/0x1c80 fs/namei.c:1778
>  walk_component+0x171/0x6a0 fs/namei.c:1945
>  link_path_walk.part.0+0x712/0xc90 fs/namei.c:2266
>  link_path_walk fs/namei.c:2190 [inline]
>  path_lookupat+0xb7/0x830 fs/namei.c:2419
>  filename_lookup+0x19f/0x560 fs/namei.c:2453
>  do_readlinkat+0xcd/0x2f0 fs/stat.c:417
>  __do_sys_readlinkat fs/stat.c:444 [inline]
>  __se_sys_readlinkat fs/stat.c:441 [inline]
>  __x64_sys_readlinkat+0x93/0xf0 fs/stat.c:441
>  do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
>  entry_SYSCALL_64_after_hwframe+0x44/0xae
> RIP: 0033:0x7fb5a7e200ba
> Code: 48 8b 0d e1 bd 2b 00 f7 d8 64 89 01 48 83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 49 89 ca b8 0b 01 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d ae bd 2b 00 f7 d8 64 89 01 48
> RSP: 002b:00007ffc9c440e38 EFLAGS: 00000202 ORIG_RAX: 000000000000010b
> RAX: ffffffffffffffda RBX: 00005604089e4380 RCX: 00007fb5a7e200ba
> RDX: 00005604089e4380 RSI: 00007ffc9c440ec0 RDI: 00000000ffffff9c
> RBP: 0000000000000064 R08: 00007fb5a80dcbc8 R09: 0000000000000070
> R10: 0000000000000063 R11: 0000000000000202 R12: 00007ffc9c440ec0
> R13: 00000000ffffff9c R14: 00007ffc9c440e90 R15: 0000000000000063
> 
> 
> ---
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> 
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