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Date:   Thu, 26 Dec 2019 13:25:09 -0800
Message-ID: <0000000000000b5f9d059aa2037f@google.com>
Subject: possible deadlock in shmem_fallocate (4)
From:   syzbot <syzbot+7a0d9d0b26efefe61780@syzkaller.appspotmail.com>
To:     akpm@linux-foundation.org, hughd@google.com,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        syzkaller-bugs@googlegroups.com
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Sender: linux-kernel-owner@vger.kernel.org
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Hello,

syzbot found the following crash on:

HEAD commit:    46cf053e Linux 5.5-rc3
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=162124aee00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=ed9d672709340e35
dashboard link: https://syzkaller.appspot.com/bug?extid=7a0d9d0b26efefe61780
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+7a0d9d0b26efefe61780@syzkaller.appspotmail.com

======================================================
WARNING: possible circular locking dependency detected
5.5.0-rc3-syzkaller #0 Not tainted
------------------------------------------------------
kswapd0/1852 is trying to acquire lock:
ffff888098919cd8 (&sb->s_type->i_mutex_key#13){+.+.}, at: inode_lock  
include/linux/fs.h:791 [inline]
ffff888098919cd8 (&sb->s_type->i_mutex_key#13){+.+.}, at:  
shmem_fallocate+0x15a/0xd40 mm/shmem.c:2735

but task is already holding lock:
ffffffff89a41e00 (fs_reclaim){+.+.}, at: __fs_reclaim_acquire+0x0/0x30  
mm/page_alloc.c:4922

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #1 (fs_reclaim){+.+.}:
        __fs_reclaim_acquire mm/page_alloc.c:4084 [inline]
        fs_reclaim_acquire.part.0+0x24/0x30 mm/page_alloc.c:4095
        fs_reclaim_acquire mm/page_alloc.c:4695 [inline]
        prepare_alloc_pages mm/page_alloc.c:4692 [inline]
        __alloc_pages_nodemask+0x52d/0x910 mm/page_alloc.c:4744
        alloc_pages_vma+0xdd/0x620 mm/mempolicy.c:2170
        shmem_alloc_page+0xc0/0x180 mm/shmem.c:1499
        shmem_alloc_and_acct_page+0x165/0x990 mm/shmem.c:1524
        shmem_getpage_gfp+0x56d/0x29a0 mm/shmem.c:1838
        shmem_getpage mm/shmem.c:154 [inline]
        shmem_write_begin+0x105/0x1e0 mm/shmem.c:2487
        generic_perform_write+0x23b/0x540 mm/filemap.c:3309
        __generic_file_write_iter+0x25e/0x630 mm/filemap.c:3438
        generic_file_write_iter+0x420/0x68e mm/filemap.c:3470
        call_write_iter include/linux/fs.h:1902 [inline]
        new_sync_write+0x4d3/0x770 fs/read_write.c:483
        __vfs_write+0xe1/0x110 fs/read_write.c:496
        vfs_write+0x268/0x5d0 fs/read_write.c:558
        ksys_write+0x14f/0x290 fs/read_write.c:611
        __do_sys_write fs/read_write.c:623 [inline]
        __se_sys_write fs/read_write.c:620 [inline]
        __x64_sys_write+0x73/0xb0 fs/read_write.c:620
        do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
        entry_SYSCALL_64_after_hwframe+0x49/0xbe

-> #0 (&sb->s_type->i_mutex_key#13){+.+.}:
        check_prev_add kernel/locking/lockdep.c:2476 [inline]
        check_prevs_add kernel/locking/lockdep.c:2581 [inline]
        validate_chain kernel/locking/lockdep.c:2971 [inline]
        __lock_acquire+0x2596/0x4a00 kernel/locking/lockdep.c:3955
        lock_acquire+0x190/0x410 kernel/locking/lockdep.c:4485
        down_write+0x93/0x150 kernel/locking/rwsem.c:1534
        inode_lock include/linux/fs.h:791 [inline]
        shmem_fallocate+0x15a/0xd40 mm/shmem.c:2735
        ashmem_shrink_scan drivers/staging/android/ashmem.c:462 [inline]
        ashmem_shrink_scan+0x370/0x510 drivers/staging/android/ashmem.c:437
        do_shrink_slab+0x40f/0xad0 mm/vmscan.c:526
        shrink_slab mm/vmscan.c:687 [inline]
        shrink_slab+0x19a/0x680 mm/vmscan.c:660
        shrink_node_memcgs mm/vmscan.c:2687 [inline]
        shrink_node+0x46a/0x1ad0 mm/vmscan.c:2791
        kswapd_shrink_node mm/vmscan.c:3539 [inline]
        balance_pgdat+0x7c8/0x11f0 mm/vmscan.c:3697
        kswapd+0x5c3/0xf30 mm/vmscan.c:3948
        kthread+0x361/0x430 kernel/kthread.c:255
        ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352

other info that might help us debug this:

  Possible unsafe locking scenario:

        CPU0                    CPU1
        ----                    ----
   lock(fs_reclaim);
                                lock(&sb->s_type->i_mutex_key#13);
                                lock(fs_reclaim);
   lock(&sb->s_type->i_mutex_key#13);

  *** DEADLOCK ***

2 locks held by kswapd0/1852:
  #0: ffffffff89a41e00 (fs_reclaim){+.+.}, at: __fs_reclaim_acquire+0x0/0x30  
mm/page_alloc.c:4922
  #1: ffffffff89a1f948 (shrinker_rwsem){++++}, at: shrink_slab  
mm/vmscan.c:677 [inline]
  #1: ffffffff89a1f948 (shrinker_rwsem){++++}, at: shrink_slab+0xe6/0x680  
mm/vmscan.c:660

stack backtrace:
CPU: 0 PID: 1852 Comm: kswapd0 Not tainted 5.5.0-rc3-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Call Trace:
  __dump_stack lib/dump_stack.c:77 [inline]
  dump_stack+0x197/0x210 lib/dump_stack.c:118
  print_circular_bug.isra.0.cold+0x163/0x172 kernel/locking/lockdep.c:1685
  check_noncircular+0x32e/0x3e0 kernel/locking/lockdep.c:1809
  check_prev_add kernel/locking/lockdep.c:2476 [inline]
  check_prevs_add kernel/locking/lockdep.c:2581 [inline]
  validate_chain kernel/locking/lockdep.c:2971 [inline]
  __lock_acquire+0x2596/0x4a00 kernel/locking/lockdep.c:3955
  lock_acquire+0x190/0x410 kernel/locking/lockdep.c:4485
  down_write+0x93/0x150 kernel/locking/rwsem.c:1534
  inode_lock include/linux/fs.h:791 [inline]
  shmem_fallocate+0x15a/0xd40 mm/shmem.c:2735
  ashmem_shrink_scan drivers/staging/android/ashmem.c:462 [inline]
  ashmem_shrink_scan+0x370/0x510 drivers/staging/android/ashmem.c:437
  do_shrink_slab+0x40f/0xad0 mm/vmscan.c:526
  shrink_slab mm/vmscan.c:687 [inline]
  shrink_slab+0x19a/0x680 mm/vmscan.c:660
  shrink_node_memcgs mm/vmscan.c:2687 [inline]
  shrink_node+0x46a/0x1ad0 mm/vmscan.c:2791
  kswapd_shrink_node mm/vmscan.c:3539 [inline]
  balance_pgdat+0x7c8/0x11f0 mm/vmscan.c:3697
  kswapd+0x5c3/0xf30 mm/vmscan.c:3948
  kthread+0x361/0x430 kernel/kthread.c:255
  ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352


---
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