Medium · published January 11, 2025
In the Linux kernel, the following vulnerability has been resolved:
btrfs: don't take dev_replace rwsem on task already holding it
Running fstests btrfs/011 with MKFS_OPTIONS="-O rst" to force the usage of
the RAID stripe-tree, we get the following splat from lockdep:
BTRFS info (device sdd): dev_replace from /dev/sdd (devid 1) to /dev/sdb started
============================================
WARNING: possible recursive locking detected
6.11.0-rc3-btrfs-for-next #599 Not tainted
--------------------------------------------
btrfs/2326 is trying to acquire lock:
ffff88810f215c98 (&fs_info->dev_replace.rwsem){++++}-{3:3}, at: btrfs_map_block+0x39f/0x2250
but task is already holding lock:
ffff88810f215c98 (&fs_info->dev_replace.rwsem){++++}-{3:3}, at: btrfs_map_block+0x39f/0x2250
other info that might help us debug this:
Possible unsafe locking scenario:
CPU0
----
lock(&fs_info->dev_replace.rwsem);
lock(&fs_info->dev_replace.rwsem);
*** DEADLOCK ***
May be due to missing lock nesting notation
1 lock held by btrfs/2326:
#0: ffff88810f215c98 (&fs_info->dev_replace.rwsem){++++}-{3:3}, at: btrfs_map_block+0x39f/0x2250
stack backtrace:
CPU: 1 UID: 0 PID: 2326 Comm: btrfs Not tainted 6.11.0-rc3-btrfs-for-next #599
Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
Call Trace:
<TASK>
dump_stack_lvl+0x5b/0x80
__lock_acquire+0x2798/0x69d0
? __pfx___lock_acquire+0x10/0x10
? __pfx___lock_acquire+0x10/0x10
lock_acquire+0x19d/0x4a0
? btrfs_map_block+0x39f/0x2250
? __pfx_lock_acquire+0x10/0x10
? find_held_lock+0x2d/0x110
? lock_is_held_type+0x8f/0x100
down_read+0x8e/0x440
? btrfs_map_block+0x39f/0x2250
? __pfx_down_read+0x10/0x10
? do_raw_read_unlock+0x44/0x70
? _raw_read_unlock+0x23/0x40
btrfs_map_block+0x39f/0x2250
? btrfs_dev_replace_by_ioctl+0xd69/0x1d00
? btrfs_bio_counter_inc_blocked+0xd9/0x2e0
? __kasan_slab_alloc+0x6e/0x70
? __pfx_btrfs_map_block+0x10/0x10
? __pfx_btrfs_bio_counter_inc_blocked+0x10/0x10
? kmem_cache_alloc_noprof+0x1f2/0x300
? mempool_alloc_noprof+0xed/0x2b0
btrfs_submit_chunk+0x28d/0x17e0
? __pfx_btrfs_submit_chunk+0x10/0x10
? bvec_alloc+0xd7/0x1b0
? bio_add_folio+0x171/0x270
? __pfx_bio_add_folio+0x10/0x10
? __kasan_check_read+0x20/0x20
btrfs_submit_bio+0x37/0x80
read_extent_buffer_pages+0x3df/0x6c0
btrfs_read_extent_buffer+0x13e/0x5f0
read_tree_block+0x81/0xe0
read_block_for_search+0x4bd/0x7a0
? __pfx_read_block_for_search+0x10/0x10
btrfs_search_slot+0x78d/0x2720
? __pfx_btrfs_search_slot+0x10/0x10
? lock_is_held_type+0x8f/0x100
? kasan_save_track+0x14/0x30
? __kasan_slab_alloc+0x6e/0x70
? kmem_cache_alloc_noprof+0x1f2/0x300
btrfs_get_raid_extent_offset+0x181/0x820
? __pfx_lock_acquire+0x10/0x10
? __pfx_btrfs_get_raid_extent_offset+0x10/0x10
? down_read+0x194/0x440
? __pfx_down_read+0x10/0x10
? do_raw_read_unlock+0x44/0x70
? _raw_read_unlock+0x23/0x40
btrfs_map_block+0x5b5/0x2250
? __pfx_btrfs_map_block+0x10/0x10
scrub_submit_initial_read+0x8fe/0x11b0
? __pfx_scrub_submit_initial_read+0x10/0x10
submit_initial_group_read+0x161/0x3a0
? lock_release+0x20e/0x710
? __pfx_submit_initial_group_read+0x10/0x10
? __pfx_lock_release+0x10/0x10
scrub_simple_mirror.isra.0+0x3eb/0x580
scrub_stripe+0xe4d/0x1440
? lock_release+0x20e/0x710
? __pfx_scrub_stripe+0x10/0x10
? __pfx_lock_release+0x10/0x10
? do_raw_read_unlock+0x44/0x70
? _raw_read_unlock+0x23/0x40
scrub_chunk+0x257/0x4a0
scrub_enumerate_chunks+0x64c/0xf70
? __mutex_unlock_slowpath+0x147/0x5f0
? __pfx_scrub_enumerate_chunks+0x10/0x10
? bit_wait_timeout+0xb0/0x170
? __up_read+0x189/0x700
? scrub_workers_get+0x231/0x300
? up_write+0x490/0x4f0
btrfs_scrub_dev+0x52e/0xcd0
? create_pending_snapshots+0x230/0x250
? __pfx_btrfs_scrub_dev+0x10/0x10
btrfs_dev_replace_by_ioctl+0xd69/0x1d00
? lock_acquire+0x19d/0x4a0
? __pfx_btrfs_dev_replace_by_ioctl+0x10/0x10
?
---truncated---