[PATCH 5.8 101/464] btrfs: fix lockdep splat from btrfs_dump_space_info

From: Greg Kroah-Hartman
Date: Mon Aug 17 2020 - 15:44:28 EST

From: Josef Bacik <josef@xxxxxxxxxxxxxx>

[ Upstream commit ab0db043c35da3477e57d4d516492b2d51a5ca0f ]

When running with -o enospc_debug you can get the following splat if one
of the dump_space_info's trip

======================================================
WARNING: possible circular locking dependency detected
5.8.0-rc5+ #20 Tainted: G OE
------------------------------------------------------
dd/563090 is trying to acquire lock:
ffff9e7dbf4f1e18 (&ctl->tree_lock){+.+.}-{2:2}, at: btrfs_dump_free_space+0x2b/0xa0 [btrfs]

but task is already holding lock:
ffff9e7e2284d428 (&cache->lock){+.+.}-{2:2}, at: btrfs_dump_space_info+0xaa/0x120 [btrfs]

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #3 (&cache->lock){+.+.}-{2:2}:
_raw_spin_lock+0x25/0x30
btrfs_add_reserved_bytes+0x3c/0x3c0 [btrfs]
find_free_extent+0x7ef/0x13b0 [btrfs]
btrfs_reserve_extent+0x9b/0x180 [btrfs]
btrfs_alloc_tree_block+0xc1/0x340 [btrfs]
alloc_tree_block_no_bg_flush+0x4a/0x60 [btrfs]
__btrfs_cow_block+0x122/0x530 [btrfs]
btrfs_cow_block+0x106/0x210 [btrfs]
commit_cowonly_roots+0x55/0x300 [btrfs]
btrfs_commit_transaction+0x4ed/0xac0 [btrfs]
sync_filesystem+0x74/0x90
generic_shutdown_super+0x22/0x100
kill_anon_super+0x14/0x30
btrfs_kill_super+0x12/0x20 [btrfs]
deactivate_locked_super+0x36/0x70
cleanup_mnt+0x104/0x160
task_work_run+0x5f/0x90
__prepare_exit_to_usermode+0x1bd/0x1c0
do_syscall_64+0x5e/0xb0
entry_SYSCALL_64_after_hwframe+0x44/0xa9

-> #2 (&space_info->lock){+.+.}-{2:2}:
_raw_spin_lock+0x25/0x30
btrfs_block_rsv_release+0x1a6/0x3f0 [btrfs]
btrfs_inode_rsv_release+0x4f/0x170 [btrfs]
btrfs_clear_delalloc_extent+0x155/0x480 [btrfs]
clear_state_bit+0x81/0x1a0 [btrfs]
__clear_extent_bit+0x25c/0x5d0 [btrfs]
clear_extent_bit+0x15/0x20 [btrfs]
btrfs_invalidatepage+0x2b7/0x3c0 [btrfs]
truncate_cleanup_page+0x47/0xe0
truncate_inode_pages_range+0x238/0x840
truncate_pagecache+0x44/0x60
btrfs_setattr+0x202/0x5e0 [btrfs]
notify_change+0x33b/0x490
do_truncate+0x76/0xd0
path_openat+0x687/0xa10
do_filp_open+0x91/0x100
do_sys_openat2+0x215/0x2d0
do_sys_open+0x44/0x80
do_syscall_64+0x52/0xb0
entry_SYSCALL_64_after_hwframe+0x44/0xa9

-> #1 (&tree->lock#2){+.+.}-{2:2}:
_raw_spin_lock+0x25/0x30
find_first_extent_bit+0x32/0x150 [btrfs]
write_pinned_extent_entries.isra.0+0xc5/0x100 [btrfs]
__btrfs_write_out_cache+0x172/0x480 [btrfs]
btrfs_write_out_cache+0x7a/0xf0 [btrfs]
btrfs_write_dirty_block_groups+0x286/0x3b0 [btrfs]
commit_cowonly_roots+0x245/0x300 [btrfs]
btrfs_commit_transaction+0x4ed/0xac0 [btrfs]
close_ctree+0xf9/0x2f5 [btrfs]
generic_shutdown_super+0x6c/0x100
kill_anon_super+0x14/0x30
btrfs_kill_super+0x12/0x20 [btrfs]
deactivate_locked_super+0x36/0x70
cleanup_mnt+0x104/0x160
task_work_run+0x5f/0x90
__prepare_exit_to_usermode+0x1bd/0x1c0
do_syscall_64+0x5e/0xb0
entry_SYSCALL_64_after_hwframe+0x44/0xa9

-> #0 (&ctl->tree_lock){+.+.}-{2:2}:
__lock_acquire+0x1240/0x2460
lock_acquire+0xab/0x360
_raw_spin_lock+0x25/0x30
btrfs_dump_free_space+0x2b/0xa0 [btrfs]
btrfs_dump_space_info+0xf4/0x120 [btrfs]
btrfs_reserve_extent+0x176/0x180 [btrfs]
__btrfs_prealloc_file_range+0x145/0x550 [btrfs]
cache_save_setup+0x28d/0x3b0 [btrfs]
btrfs_start_dirty_block_groups+0x1fc/0x4f0 [btrfs]
btrfs_commit_transaction+0xcc/0xac0 [btrfs]
btrfs_alloc_data_chunk_ondemand+0x162/0x4c0 [btrfs]
btrfs_check_data_free_space+0x4c/0xa0 [btrfs]
btrfs_buffered_write.isra.0+0x19b/0x740 [btrfs]
btrfs_file_write_iter+0x3cf/0x610 [btrfs]
new_sync_write+0x11e/0x1b0
vfs_write+0x1c9/0x200
ksys_write+0x68/0xe0
do_syscall_64+0x52/0xb0
entry_SYSCALL_64_after_hwframe+0x44/0xa9

other info that might help us debug this:

Chain exists of:
&ctl->tree_lock --> &space_info->lock --> &cache->lock

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(&cache->lock);
lock(&space_info->lock);
lock(&cache->lock);
lock(&ctl->tree_lock);

*** DEADLOCK ***

6 locks held by dd/563090:
#0: ffff9e7e21d18448 (sb_writers#14){.+.+}-{0:0}, at: vfs_write+0x195/0x200
#1: ffff9e7dd0410ed8 (&sb->s_type->i_mutex_key#19){++++}-{3:3}, at: btrfs_file_write_iter+0x86/0x610 [btrfs]
#2: ffff9e7e21d18638 (sb_internal#2){.+.+}-{0:0}, at: start_transaction+0x40b/0x5b0 [btrfs]
#3: ffff9e7e1f05d688 (&cur_trans->cache_write_mutex){+.+.}-{3:3}, at: btrfs_start_dirty_block_groups+0x158/0x4f0 [btrfs]
#4: ffff9e7e2284ddb8 (&space_info->groups_sem){++++}-{3:3}, at: btrfs_dump_space_info+0x69/0x120 [btrfs]
#5: ffff9e7e2284d428 (&cache->lock){+.+.}-{2:2}, at: btrfs_dump_space_info+0xaa/0x120 [btrfs]

stack backtrace:
CPU: 3 PID: 563090 Comm: dd Tainted: G OE 5.8.0-rc5+ #20
Hardware name: To Be Filled By O.E.M. To Be Filled By O.E.M./890FX Deluxe5, BIOS P1.40 05/03/2011
Call Trace:
dump_stack+0x96/0xd0
check_noncircular+0x162/0x180
__lock_acquire+0x1240/0x2460
? wake_up_klogd.part.0+0x30/0x40
lock_acquire+0xab/0x360
? btrfs_dump_free_space+0x2b/0xa0 [btrfs]
_raw_spin_lock+0x25/0x30
? btrfs_dump_free_space+0x2b/0xa0 [btrfs]
btrfs_dump_free_space+0x2b/0xa0 [btrfs]
btrfs_dump_space_info+0xf4/0x120 [btrfs]
btrfs_reserve_extent+0x176/0x180 [btrfs]
__btrfs_prealloc_file_range+0x145/0x550 [btrfs]
? btrfs_qgroup_reserve_data+0x1d/0x60 [btrfs]
cache_save_setup+0x28d/0x3b0 [btrfs]
btrfs_start_dirty_block_groups+0x1fc/0x4f0 [btrfs]
btrfs_commit_transaction+0xcc/0xac0 [btrfs]
? start_transaction+0xe0/0x5b0 [btrfs]
btrfs_alloc_data_chunk_ondemand+0x162/0x4c0 [btrfs]
btrfs_check_data_free_space+0x4c/0xa0 [btrfs]
btrfs_buffered_write.isra.0+0x19b/0x740 [btrfs]
? ktime_get_coarse_real_ts64+0xa8/0xd0
? trace_hardirqs_on+0x1c/0xe0
btrfs_file_write_iter+0x3cf/0x610 [btrfs]
new_sync_write+0x11e/0x1b0
vfs_write+0x1c9/0x200
ksys_write+0x68/0xe0
do_syscall_64+0x52/0xb0
entry_SYSCALL_64_after_hwframe+0x44/0xa9

This is because we're holding the block_group->lock while trying to dump
the free space cache. However we don't need this lock, we just need it
to read the values for the printk, so move the free space cache dumping
outside of the block group lock.

Signed-off-by: Josef Bacik <josef@xxxxxxxxxxxxxx>
Reviewed-by: David Sterba <dsterba@xxxxxxxx>
Signed-off-by: David Sterba <dsterba@xxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
fs/btrfs/space-info.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/btrfs/space-info.c b/fs/btrfs/space-info.c
index c7bd3fdd77928..475968ccbd1d1 100644
--- a/fs/btrfs/space-info.c
+++ b/fs/btrfs/space-info.c
@@ -468,8 +468,8 @@ void btrfs_dump_space_info(struct btrfs_fs_info *fs_info,
"block group %llu has %llu bytes, %llu used %llu pinned %llu reserved %s",
cache->start, cache->length, cache->used, cache->pinned,
cache->reserved, cache->ro ? "[readonly]" : "");
- btrfs_dump_free_space(cache, bytes);
spin_unlock(&cache->lock);
+ btrfs_dump_free_space(cache, bytes);
}
if (++index < BTRFS_NR_RAID_TYPES)
goto again;
--
2.25.1