Re: mm: sleeping function called from invalid context shmem_undo_range

[Hillf Danton]

On January 31, 2017 5:32 PM Kirill A. Shutemov wrote: 
> On Tue, Jan 31, 2017 at 09:27:41AM +0100, Dmitry Vyukov wrote:
> > Hello,
> >
> > I've got the following report while running syzkaller fuzzer on
> > fd694aaa46c7ed811b72eb47d5eb11ce7ab3f7f1:
> 
> This should help:
> 
> From fb85b3fe273decb11c558d56257193424b8f071a Mon Sep 17 00:00:00 2001
> From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
> Date: Tue, 31 Jan 2017 12:22:26 +0300
> Subject: [PATCH] shmem: fix sleeping from atomic context
> 
> Syzkaller fuzzer managed to trigger this:
> 
> BUG: sleeping function called from invalid context at mm/shmem.c:852
> in_atomic(): 1, irqs_disabled(): 0, pid: 529, name: khugepaged
> 3 locks held by khugepaged/529:
>  #0:  (shrinker_rwsem){++++..}, at: [<ffffffff818d7ef1>]
> shrink_slab.part.59+0x121/0xd30 mm/vmscan.c:451
>  #1:  (&type->s_umount_key#29){++++..}, at: [<ffffffff81a63630>]
> trylock_super+0x20/0x100 fs/super.c:392
>  #2:  (&(&sbinfo->shrinklist_lock)->rlock){+.+.-.}, at:
> [<ffffffff818fd83e>] spin_lock include/linux/spinlock.h:302 [inline]
>  #2:  (&(&sbinfo->shrinklist_lock)->rlock){+.+.-.}, at:
> [<ffffffff818fd83e>] shmem_unused_huge_shrink+0x28e/0x1490
> mm/shmem.c:427
> CPU: 2 PID: 529 Comm: khugepaged Not tainted 4.10.0-rc5+ #201
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
> Call Trace:
>  __dump_stack lib/dump_stack.c:15 [inline]
>  dump_stack+0x2ee/0x3ef lib/dump_stack.c:51
>  ___might_sleep+0x47e/0x650 kernel/sched/core.c:7780
>  shmem_undo_range+0xb20/0x2710 mm/shmem.c:852
>  shmem_truncate_range+0x27/0xa0 mm/shmem.c:939
>  shmem_evict_inode+0x35f/0xca0 mm/shmem.c:1030
>  evict+0x46e/0x980 fs/inode.c:553
>  iput_final fs/inode.c:1515 [inline]
>  iput+0x589/0xb20 fs/inode.c:1542
>  shmem_unused_huge_shrink+0xbad/0x1490 mm/shmem.c:446
>  shmem_unused_huge_scan+0x10c/0x170 mm/shmem.c:512
>  super_cache_scan+0x376/0x450 fs/super.c:106
>  do_shrink_slab mm/vmscan.c:378 [inline]
>  shrink_slab.part.59+0x543/0xd30 mm/vmscan.c:481
>  shrink_slab mm/vmscan.c:2592 [inline]
>  shrink_node+0x2c7/0x870 mm/vmscan.c:2592
>  shrink_zones mm/vmscan.c:2734 [inline]
>  do_try_to_free_pages+0x369/0xc80 mm/vmscan.c:2776
>  try_to_free_pages+0x3c6/0x900 mm/vmscan.c:2982
>  __perform_reclaim mm/page_alloc.c:3301 [inline]
>  __alloc_pages_direct_reclaim mm/page_alloc.c:3322 [inline]
>  __alloc_pages_slowpath+0xa24/0x1c30 mm/page_alloc.c:3683
>  __alloc_pages_nodemask+0x544/0xae0 mm/page_alloc.c:3848
>  __alloc_pages include/linux/gfp.h:426 [inline]
>  __alloc_pages_node include/linux/gfp.h:439 [inline]
>  khugepaged_alloc_page+0xc2/0x1b0 mm/khugepaged.c:750
>  collapse_huge_page+0x182/0x1fe0 mm/khugepaged.c:955
>  khugepaged_scan_pmd+0xfdf/0x12a0 mm/khugepaged.c:1208
>  khugepaged_scan_mm_slot mm/khugepaged.c:1727 [inline]
>  khugepaged_do_scan mm/khugepaged.c:1808 [inline]
>  khugepaged+0xe9b/0x1590 mm/khugepaged.c:1853
>  kthread+0x326/0x3f0 kernel/kthread.c:227
>  ret_from_fork+0x31/0x40 arch/x86/entry/entry_64.S:430
> 
> The iput() from atomic context was a bad idea: if after igrab() somebody
> else calls iput() and we left with the last inode reference, our iput()
> would lead to inode eviction and therefore sleeping.
> 
> This patch should fix the situation.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> Reported-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
> ---
Acked-by: Hillf Danton <hillf.zj@xxxxxxxxxxxxxxx>