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

[Dmitry Vyukov]

On Mon, Apr 5, 2021 at 7:35 AM syzbot
<syzbot+3d5082ab6eec95ad4231@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
>
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit:    d19cc4bf Merge tag 'trace-v5.12-rc5' of git://git.kernel.o..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=17a22d16d00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=78ef1d159159890
> dashboard link: https://syzkaller.appspot.com/bug?extid=3d5082ab6eec95ad4231
>
> 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+3d5082ab6eec95ad4231@xxxxxxxxxxxxxxxxxxxxxxxxx

#syz dup: WARNING: suspicious RCU usage in getname_flags

> 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
> 1 lock held by syz-executor.5/8582:
>  #0: ffff888029093218 (&mm->mmap_lock#2){++++}-{3:3}, at: mmap_read_trylock include/linux/mmap_lock.h:136 [inline]
>  #0: ffff888029093218 (&mm->mmap_lock#2){++++}-{3:3}, at: do_user_addr_fault+0x285/0x1210 arch/x86/mm/fault.c:1331
>
> stack backtrace:
> CPU: 0 PID: 8582 Comm: syz-executor.5 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
>  do_user_addr_fault+0x2c2/0x1210 arch/x86/mm/fault.c:1348
>  handle_page_fault arch/x86/mm/fault.c:1475 [inline]
>  exc_page_fault+0x9e/0x180 arch/x86/mm/fault.c:1531
>  asm_exc_page_fault+0x1e/0x30 arch/x86/include/asm/idtentry.h:577
> RIP: 0033:0x406f13
> Code: 00 00 e8 a0 a1 ff ff 85 c0 74 4e 8b 54 24 0c 49 8b 37 31 c0 48 8d 3d 79 7f 0b 00 e8 27 c3 ff ff 8b 44 24 6c 49 8d 4f 60 89 de <4d> 89 a7 b8 00 00 00 ba 40 00 00 00 44 89 ef 41 89 87 b4 00 00 00
> RSP: 002b:00007fff2a8e7140 EFLAGS: 00010202
> RAX: 0000000000000005 RBX: 0000000000000000 RCX: 0000000000544420
> RDX: 0000000000000002 RSI: 0000000000000000 RDI: 00000000004bee7d
> RBP: 00007fff2a8e7160 R08: 00007fff2a8e715c R09: 00007fff2a8e71f0
> R10: 00007fff2a8e71c0 R11: 0000000000000202 R12: 00007fff2a8e71c0
> R13: 0000000000000003 R14: 00007fff2a8e715c R15: 00000000005443c0
>
>
> ---
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>
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