[syzbot] WARNING: suspicious RCU usage in getname_flags

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    2bb25b3a Merge tag 'mips-fixes_5.12_3' of git://git.kernel..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1284cc31d00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=78ef1d159159890
dashboard link: https://syzkaller.appspot.com/bug?extid=dde0cc33951735441301

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+dde0cc33951735441301@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: 0 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
 __might_fault+0x6e/0x180 mm/memory.c:5018
 strncpy_from_user+0x2f/0x3e0 lib/strncpy_from_user.c:117
 getname_flags.part.0+0x95/0x4f0 fs/namei.c:149
 getname_flags fs/namei.c:2733 [inline]
 user_path_at_empty+0xa1/0x100 fs/namei.c:2733
 user_path_at include/linux/namei.h:60 [inline]
 do_faccessat+0x127/0x850 fs/open.c:425
 do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x7f840445f9c7
Code: 83 c4 08 48 3d 01 f0 ff ff 73 01 c3 48 8b 0d c8 d4 2b 00 f7 d8 64 89 01 48 83 c8 ff c3 66 0f 1f 44 00 00 b8 15 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d a1 d4 2b 00 f7 d8 64 89 01 48
RSP: 002b:00007ffdc40178d8 EFLAGS: 00000246 ORIG_RAX: 0000000000000015
RAX: ffffffffffffffda RBX: 0000564d558c9760 RCX: 00007f840445f9c7
RDX: 00746e657665752f RSI: 0000000000000000 RDI: 00007ffdc40178e0
RBP: 00007ffdc4017960 R08: 0000000000004400 R09: 0000000000001010
R10: 0000000000000020 R11: 0000000000000246 R12: 0000564d557b1856
R13: 0000564d558ed190 R14: 00007ffdc40178e0 R15: 0000564d558fe590


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