======================================================
WARNING: possible circular locking dependency detected
5.6.0-rc6-syzkaller #0 Not tainted
------------------------------------------------------
kswapd0/1876 is trying to acquire lock:
ffff8880a185d798 (&sb->s_type->i_mutex_key#13){+.+.}, at: inode_lock include/linux/fs.h:792 [inline]
ffff8880a185d798 (&sb->s_type->i_mutex_key#13){+.+.}, at: shmem_fallocate+0x15a/0xd40 mm/shmem.c:2736

but task is already holding lock:
ffffffff89851ba0 (fs_reclaim){+.+.}, at: __fs_reclaim_acquire+0x0/0x30 mm/page_alloc.c:4897

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:4073 [inline]
       fs_reclaim_acquire.part.0+0x20/0x30 mm/page_alloc.c:4084
       fs_reclaim_acquire mm/page_alloc.c:4670 [inline]
       prepare_alloc_pages mm/page_alloc.c:4667 [inline]
       __alloc_pages_nodemask+0x4e0/0x820 mm/page_alloc.c:4719
       alloc_pages_vma+0xd9/0x600 mm/mempolicy.c:2174
       shmem_alloc_page+0xb0/0x170 mm/shmem.c:1499
       shmem_alloc_and_acct_page+0x160/0x980 mm/shmem.c:1524
       shmem_getpage_gfp+0x51a/0x2860 mm/shmem.c:1838
       shmem_getpage mm/shmem.c:154 [inline]
       shmem_write_begin+0x102/0x1e0 mm/shmem.c:2488
       generic_perform_write+0x20a/0x4e0 mm/filemap.c:3287
       __generic_file_write_iter+0x24c/0x610 mm/filemap.c:3416
       generic_file_write_iter+0x3f0/0x62d mm/filemap.c:3448
       call_write_iter include/linux/fs.h:1902 [inline]
       new_sync_write+0x49c/0x700 fs/read_write.c:483
       __vfs_write+0xc9/0x100 fs/read_write.c:496
       vfs_write+0x262/0x5c0 fs/read_write.c:558
       ksys_write+0x127/0x250 fs/read_write.c:611
       do_syscall_64+0xf6/0x7d0 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:2475 [inline]
       check_prevs_add kernel/locking/lockdep.c:2580 [inline]
       validate_chain kernel/locking/lockdep.c:2970 [inline]
       __lock_acquire+0x201b/0x3ca0 kernel/locking/lockdep.c:3954
       lock_acquire+0x197/0x420 kernel/locking/lockdep.c:4484
       down_write+0x8d/0x150 kernel/locking/rwsem.c:1534
       inode_lock include/linux/fs.h:792 [inline]
       shmem_fallocate+0x15a/0xd40 mm/shmem.c:2736
       ashmem_shrink_scan drivers/staging/android/ashmem.c:490 [inline]
       ashmem_shrink_scan+0x34d/0x500 drivers/staging/android/ashmem.c:465
       do_shrink_slab+0x3fc/0xab0 mm/vmscan.c:512
       shrink_slab mm/vmscan.c:673 [inline]
       shrink_slab+0x16f/0x5f0 mm/vmscan.c:646
       shrink_node_memcgs mm/vmscan.c:2676 [inline]
       shrink_node+0x477/0x1b20 mm/vmscan.c:2780
       kswapd_shrink_node mm/vmscan.c:3526 [inline]
       balance_pgdat+0x76c/0x1130 mm/vmscan.c:3684
       kswapd+0x571/0xe40 mm/vmscan.c:3935
       kthread+0x357/0x430 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 kswapd0/1876:
 #0: ffffffff89851ba0 (fs_reclaim){+.+.}, at: __fs_reclaim_acquire+0x0/0x30 mm/page_alloc.c:4897
 #1: ffffffff8982d248 (shrinker_rwsem){++++}, at: shrink_slab mm/vmscan.c:663 [inline]
 #1: ffffffff8982d248 (shrinker_rwsem){++++}, at: shrink_slab+0xc7/0x5f0 mm/vmscan.c:646

stack backtrace:
CPU: 0 PID: 1876 Comm: kswapd0 Not tainted 5.6.0-rc6-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+0x188/0x20d lib/dump_stack.c:118
 check_noncircular+0x32e/0x3e0 kernel/locking/lockdep.c:1808
 check_prev_add kernel/locking/lockdep.c:2475 [inline]
 check_prevs_add kernel/locking/lockdep.c:2580 [inline]
 validate_chain kernel/locking/lockdep.c:2970 [inline]
 __lock_acquire+0x201b/0x3ca0 kernel/locking/lockdep.c:3954
 lock_acquire+0x197/0x420 kernel/locking/lockdep.c:4484
 down_write+0x8d/0x150 kernel/locking/rwsem.c:1534
 inode_lock include/linux/fs.h:792 [inline]
 shmem_fallocate+0x15a/0xd40 mm/shmem.c:2736
 ashmem_shrink_scan drivers/staging/android/ashmem.c:490 [inline]
 ashmem_shrink_scan+0x34d/0x500 drivers/staging/android/ashmem.c:465
 do_shrink_slab+0x3fc/0xab0 mm/vmscan.c:512
 shrink_slab mm/vmscan.c:673 [inline]
 shrink_slab+0x16f/0x5f0 mm/vmscan.c:646
 shrink_node_memcgs mm/vmscan.c:2676 [inline]
 shrink_node+0x477/0x1b20 mm/vmscan.c:2780
 kswapd_shrink_node mm/vmscan.c:3526 [inline]
 balance_pgdat+0x76c/0x1130 mm/vmscan.c:3684
 kswapd+0x571/0xe40 mm/vmscan.c:3935
 kthread+0x357/0x430 kernel/kthread.c:255
 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352