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Subjectpossible deadlock in shmem_fallocate (4)
From
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


---
This bug is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzkaller@googlegroups.com.

syzbot will keep track of this bug report. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

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