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btrfs: don't take dev_replace rwsem on task already holding it
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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 torvalds#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 torvalds#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
  ? lock_release+0x20e/0x710
  ? btrfs_ioctl+0xa09/0x74f0
  ? __pfx_lock_release+0x10/0x10
  ? do_raw_spin_lock+0x11e/0x240
  ? __pfx_do_raw_spin_lock+0x10/0x10
  btrfs_ioctl+0xa14/0x74f0
  ? lock_acquire+0x19d/0x4a0
  ? find_held_lock+0x2d/0x110
  ? __pfx_btrfs_ioctl+0x10/0x10
  ? lock_release+0x20e/0x710
  ? do_sigaction+0x3f0/0x860
  ? __pfx_do_vfs_ioctl+0x10/0x10
  ? do_raw_spin_lock+0x11e/0x240
  ? lockdep_hardirqs_on_prepare+0x270/0x3e0
  ? _raw_spin_unlock_irq+0x28/0x50
  ? do_sigaction+0x3f0/0x860
  ? __pfx_do_sigaction+0x10/0x10
  ? __x64_sys_rt_sigaction+0x18e/0x1e0
  ? __pfx___x64_sys_rt_sigaction+0x10/0x10
  ? __x64_sys_close+0x7c/0xd0
  __x64_sys_ioctl+0x137/0x190
  do_syscall_64+0x71/0x140
  entry_SYSCALL_64_after_hwframe+0x76/0x7e
 RIP: 0033:0x7f0bd1114f9b
 Code: Unable to access opcode bytes at 0x7f0bd1114f71.
 RSP: 002b:00007ffc8a8c3130 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
 RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00007f0bd1114f9b
 RDX: 00007ffc8a8c35e0 RSI: 00000000ca289435 RDI: 0000000000000003
 RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000007
 R10: 0000000000000008 R11: 0000000000000246 R12: 00007ffc8a8c6c85
 R13: 00000000398e72a0 R14: 0000000000004361 R15: 0000000000000004
  </TASK>

This happens because on RAID stripe-tree filesystems we recurse back into
btrfs_map_block() on scrub to perform the logical to device physical
mapping.

But as the device replace task is already holding the dev_replace::rwsem
we deadlock.

So don't take the dev_replace::rwsem in case our task is the task performing
the device replace.

Suggested-by: Filipe Manana <[email protected]>
Signed-off-by: Johannes Thumshirn <[email protected]>
Reviewed-by: Filipe Manana <[email protected]>
Signed-off-by: David Sterba <[email protected]>
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@morbidrsa @kdave
morbidrsa authored and kdave committed Oct 10, 2024
1 parent 1d227fc commit a1fe3c4
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Showing 3 changed files with 9 additions and 3 deletions.
2 changes: 2 additions & 0 deletions fs/btrfs/dev-replace.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -641,6 +641,7 @@ static int btrfs_dev_replace_start(struct btrfs_fs_info *fs_info,
return ret;

down_write(&dev_replace->rwsem);
dev_replace->replace_task = current;
switch (dev_replace->replace_state) {
case BTRFS_IOCTL_DEV_REPLACE_STATE_NEVER_STARTED:
case BTRFS_IOCTL_DEV_REPLACE_STATE_FINISHED:
Expand Down Expand Up @@ -994,6 +995,7 @@ static int btrfs_dev_replace_finishing(struct btrfs_fs_info *fs_info,
list_add(&tgt_device->dev_alloc_list, &fs_devices->alloc_list);
fs_devices->rw_devices++;

dev_replace->replace_task = NULL;
up_write(&dev_replace->rwsem);
btrfs_rm_dev_replace_blocked(fs_info);

Expand Down
2 changes: 2 additions & 0 deletions fs/btrfs/fs.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -317,6 +317,8 @@ struct btrfs_dev_replace {

struct percpu_counter bio_counter;
wait_queue_head_t replace_wait;

struct task_struct *replace_task;
};

/*
Expand Down
8 changes: 5 additions & 3 deletions fs/btrfs/volumes.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -6480,13 +6480,15 @@ int btrfs_map_block(struct btrfs_fs_info *fs_info, enum btrfs_map_op op,
max_len = btrfs_max_io_len(map, map_offset, &io_geom);
*length = min_t(u64, map->chunk_len - map_offset, max_len);

down_read(&dev_replace->rwsem);
if (dev_replace->replace_task != current)
down_read(&dev_replace->rwsem);

dev_replace_is_ongoing = btrfs_dev_replace_is_ongoing(dev_replace);
/*
* Hold the semaphore for read during the whole operation, write is
* requested at commit time but must wait.
*/
if (!dev_replace_is_ongoing)
if (!dev_replace_is_ongoing && dev_replace->replace_task != current)
up_read(&dev_replace->rwsem);

switch (map->type & BTRFS_BLOCK_GROUP_PROFILE_MASK) {
Expand Down Expand Up @@ -6626,7 +6628,7 @@ int btrfs_map_block(struct btrfs_fs_info *fs_info, enum btrfs_map_op op,
bioc->mirror_num = io_geom.mirror_num;

out:
if (dev_replace_is_ongoing) {
if (dev_replace_is_ongoing && dev_replace->replace_task != current) {
lockdep_assert_held(&dev_replace->rwsem);
/* Unlock and let waiting writers proceed */
up_read(&dev_replace->rwsem);
Expand Down

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