syzbot

======================================================
WARNING: possible circular locking dependency detected
5.3.0-rc6-next-20190830 #75 Not tainted
------------------------------------------------------
kswapd0/1770 is trying to acquire lock:
ffff8880a0b9b780 (&sb->s_type->i_mutex_key#13){+.+.}, at: inode_lock include/linux/fs.h:789 [inline]
ffff8880a0b9b780 (&sb->s_type->i_mutex_key#13){+.+.}, at: shmem_fallocate+0x15a/0xc60 mm/shmem.c:2728

but task is already holding lock:
ffffffff89042f80 (fs_reclaim){+.+.}, at: __fs_reclaim_acquire+0x0/0x30 mm/page_alloc.c:4889

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:4075 [inline]
       fs_reclaim_acquire.part.0+0x24/0x30 mm/page_alloc.c:4086
       fs_reclaim_acquire mm/page_alloc.c:4662 [inline]
       prepare_alloc_pages mm/page_alloc.c:4659 [inline]
       __alloc_pages_nodemask+0x52f/0x900 mm/page_alloc.c:4711
       alloc_pages_vma+0x1bc/0x3f0 mm/mempolicy.c:2114
       shmem_alloc_page+0xbd/0x180 mm/shmem.c:1496
       shmem_alloc_and_acct_page+0x165/0x990 mm/shmem.c:1521
       shmem_getpage_gfp+0x598/0x2680 mm/shmem.c:1835
       shmem_getpage mm/shmem.c:152 [inline]
       shmem_write_begin+0x105/0x1e0 mm/shmem.c:2480
       generic_perform_write+0x23b/0x540 mm/filemap.c:3304
       __generic_file_write_iter+0x25e/0x630 mm/filemap.c:3433
       generic_file_write_iter+0x420/0x690 mm/filemap.c:3465
       call_write_iter include/linux/fs.h:1890 [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/0x760 arch/x86/entry/common.c:290
       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:4487
       down_write+0x93/0x150 kernel/locking/rwsem.c:1534
       inode_lock include/linux/fs.h:789 [inline]
       shmem_fallocate+0x15a/0xc60 mm/shmem.c:2728
       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/0xa30 mm/vmscan.c:560
       shrink_slab mm/vmscan.c:721 [inline]
       shrink_slab+0x19a/0x680 mm/vmscan.c:694
       shrink_node+0x223/0x12e0 mm/vmscan.c:2807
       kswapd_shrink_node mm/vmscan.c:3549 [inline]
       balance_pgdat+0x57c/0xea0 mm/vmscan.c:3707
       kswapd+0x5c3/0xf30 mm/vmscan.c:3958
       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 kswapd0/1770:
 #0: ffffffff89042f80 (fs_reclaim){+.+.}, at: __fs_reclaim_acquire+0x0/0x30 mm/page_alloc.c:4889
 #1: ffffffff8901ffe8 (shrinker_rwsem){++++}, at: shrink_slab mm/vmscan.c:711 [inline]
 #1: ffffffff8901ffe8 (shrinker_rwsem){++++}, at: shrink_slab+0xe6/0x680 mm/vmscan.c:694

stack backtrace:
CPU: 0 PID: 1770 Comm: kswapd0 Not tainted 5.3.0-rc6-next-20190830 #75
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+0x172/0x1f0 lib/dump_stack.c:113
 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:4487
 down_write+0x93/0x150 kernel/locking/rwsem.c:1534
 inode_lock include/linux/fs.h:789 [inline]
 shmem_fallocate+0x15a/0xc60 mm/shmem.c:2728
 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/0xa30 mm/vmscan.c:560
 shrink_slab mm/vmscan.c:721 [inline]
 shrink_slab+0x19a/0x680 mm/vmscan.c:694
 shrink_node+0x223/0x12e0 mm/vmscan.c:2807
 kswapd_shrink_node mm/vmscan.c:3549 [inline]
 balance_pgdat+0x57c/0xea0 mm/vmscan.c:3707
 kswapd+0x5c3/0xf30 mm/vmscan.c:3958
 kthread+0x361/0x430 kernel/kthread.c:255
 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352