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

[Matthew Wilcox <willy@infradead.org>]

#syz dup: WARNING: suspicious RCU usage in getname_flags

On Sat, Apr 03, 2021 at 07:35:16PM -0700, syzbot 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=1611e681d00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=78ef1d159159890
> dashboard link: https://syzkaller.appspot.com/bug?extid=7a0c25f9520c969c15f5
> 
> 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+7a0c25f9520c969c15f5@syzkaller.appspotmail.com
> 
> =============================
> 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.2/10002:
>  #0: ffff8880129669d8 (&mm->mmap_lock#2){++++}-{3:3}, at: mmap_read_trylock include/linux/mmap_lock.h:136 [inline]
>  #0: ffff8880129669d8 (&mm->mmap_lock#2){++++}-{3:3}, at: do_user_addr_fault+0x285/0x1210 arch/x86/mm/fault.c:1331
> 
> stack backtrace:
> CPU: 0 PID: 10002 Comm: syz-executor.2 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
>  process_huge_page mm/memory.c:5051 [inline]
>  clear_huge_page+0x9c/0x560 mm/memory.c:5112
>  __do_huge_pmd_anonymous_page mm/huge_memory.c:607 [inline]
>  do_huge_pmd_anonymous_page+0x60e/0x2570 mm/huge_memory.c:772
>  create_huge_pmd mm/memory.c:4189 [inline]
>  __handle_mm_fault+0x2e59/0x4f70 mm/memory.c:4424
>  handle_mm_fault+0x1bc/0x7e0 mm/memory.c:4551
>  do_user_addr_fault+0x483/0x1210 arch/x86/mm/fault.c:1390
>  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: 0033:0x461b6d
> Code: 48 01 d0 eb 0b 0f 1f 84 00 00 00 00 00 48 89 f8 48 83 fa 20 72 49 48 83 fa 40 0f 87 9f 00 00 00 c5 fe 6f 06 c5 fe 6f 4c 16 e0 <c5> fe 7f 07 c5 fe 7f 4c 17 e0 c5 f8 77 c3 48 3b 15 7e 8e 04 01 0f
> RSP: 002b:00007fffc28c60c8 EFLAGS: 00010287
> RAX: 0000000020000080 RBX: 0000000000000003 RCX: 0000000000570000
> RDX: 000000000000002b RSI: 0000000000570020 RDI: 0000000020000080
> RBP: 00007fffc28c6188 R08: 0000000000970000 R09: 00007fffc2907090
> R10: 000000000000a8e8 R11: 0000000000000000 R12: 0000000000000001
> R13: 0000000000000000 R14: 000000000056bf60 R15: 0000000000035790
> 
> 
> ---
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