btrfs: protect fs_info->caching_block_groups by block_group_cache_lock
I got the following lockdep splat ====================================================== WARNING: possible circular locking dependency detected 5.9.0+ #101 Not tainted ------------------------------------------------------ btrfs-cleaner/3445 is trying to acquire lock: ffff89dbec39ab48 (btrfs-root-00){++++}-{3:3}, at: __btrfs_tree_read_lock+0x32/0x170 but task is already holding lock: ffff89dbeaf28a88 (&fs_info->commit_root_sem){++++}-{3:3}, at: btrfs_find_all_roots+0x41/0x80 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #2 (&fs_info->commit_root_sem){++++}-{3:3}: down_write+0x3d/0x70 btrfs_cache_block_group+0x2d5/0x510 find_free_extent+0xb6e/0x12f0 btrfs_reserve_extent+0xb3/0x1b0 btrfs_alloc_tree_block+0xb1/0x330 alloc_tree_block_no_bg_flush+0x4f/0x60 __btrfs_cow_block+0x11d/0x580 btrfs_cow_block+0x10c/0x220 commit_cowonly_roots+0x47/0x2e0 btrfs_commit_transaction+0x595/0xbd0 sync_filesystem+0x74/0x90 generic_shutdown_super+0x22/0x100 kill_anon_super+0x14/0x30 btrfs_kill_super+0x12/0x20 deactivate_locked_super+0x36/0xa0 cleanup_mnt+0x12d/0x190 task_work_run+0x5c/0xa0 exit_to_user_mode_prepare+0x1df/0x200 syscall_exit_to_user_mode+0x54/0x280 entry_SYSCALL_64_after_hwframe+0x44/0xa9 -> #1 (&space_info->groups_sem){++++}-{3:3}: down_read+0x40/0x130 find_free_extent+0x2ed/0x12f0 btrfs_reserve_extent+0xb3/0x1b0 btrfs_alloc_tree_block+0xb1/0x330 alloc_tree_block_no_bg_flush+0x4f/0x60 __btrfs_cow_block+0x11d/0x580 btrfs_cow_block+0x10c/0x220 commit_cowonly_roots+0x47/0x2e0 btrfs_commit_transaction+0x595/0xbd0 sync_filesystem+0x74/0x90 generic_shutdown_super+0x22/0x100 kill_anon_super+0x14/0x30 btrfs_kill_super+0x12/0x20 deactivate_locked_super+0x36/0xa0 cleanup_mnt+0x12d/0x190 task_work_run+0x5c/0xa0 exit_to_user_mode_prepare+0x1df/0x200 syscall_exit_to_user_mode+0x54/0x280 entry_SYSCALL_64_after_hwframe+0x44/0xa9 -> #0 (btrfs-root-00){++++}-{3:3}: __lock_acquire+0x1167/0x2150 lock_acquire+0xb9/0x3d0 down_read_nested+0x43/0x130 __btrfs_tree_read_lock+0x32/0x170 __btrfs_read_lock_root_node+0x3a/0x50 btrfs_search_slot+0x614/0x9d0 btrfs_find_root+0x35/0x1b0 btrfs_read_tree_root+0x61/0x120 btrfs_get_root_ref+0x14b/0x600 find_parent_nodes+0x3e6/0x1b30 btrfs_find_all_roots_safe+0xb4/0x130 btrfs_find_all_roots+0x60/0x80 btrfs_qgroup_trace_extent_post+0x27/0x40 btrfs_add_delayed_data_ref+0x3fd/0x460 btrfs_free_extent+0x42/0x100 __btrfs_mod_ref+0x1d7/0x2f0 walk_up_proc+0x11c/0x400 walk_up_tree+0xf0/0x180 btrfs_drop_snapshot+0x1c7/0x780 btrfs_clean_one_deleted_snapshot+0xfb/0x110 cleaner_kthread+0xd4/0x140 kthread+0x13a/0x150 ret_from_fork+0x1f/0x30 other info that might help us debug this: Chain exists of: btrfs-root-00 --> &space_info->groups_sem --> &fs_info->commit_root_sem Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(&fs_info->commit_root_sem); lock(&space_info->groups_sem); lock(&fs_info->commit_root_sem); lock(btrfs-root-00); *** DEADLOCK *** 3 locks held by btrfs-cleaner/3445: #0: ffff89dbeaf28838 (&fs_info->cleaner_mutex){+.+.}-{3:3}, at: cleaner_kthread+0x6e/0x140 #1: ffff89dbeb6c7640 (sb_internal){.+.+}-{0:0}, at: start_transaction+0x40b/0x5c0 #2: ffff89dbeaf28a88 (&fs_info->commit_root_sem){++++}-{3:3}, at: btrfs_find_all_roots+0x41/0x80 stack backtrace: CPU: 0 PID: 3445 Comm: btrfs-cleaner Not tainted 5.9.0+ #101 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-2.fc32 04/01/2014 Call Trace: dump_stack+0x8b/0xb0 check_noncircular+0xcf/0xf0 __lock_acquire+0x1167/0x2150 ? __bfs+0x42/0x210 lock_acquire+0xb9/0x3d0 ? __btrfs_tree_read_lock+0x32/0x170 down_read_nested+0x43/0x130 ? __btrfs_tree_read_lock+0x32/0x170 __btrfs_tree_read_lock+0x32/0x170 __btrfs_read_lock_root_node+0x3a/0x50 btrfs_search_slot+0x614/0x9d0 ? find_held_lock+0x2b/0x80 btrfs_find_root+0x35/0x1b0 ? do_raw_spin_unlock+0x4b/0xa0 btrfs_read_tree_root+0x61/0x120 btrfs_get_root_ref+0x14b/0x600 find_parent_nodes+0x3e6/0x1b30 btrfs_find_all_roots_safe+0xb4/0x130 btrfs_find_all_roots+0x60/0x80 btrfs_qgroup_trace_extent_post+0x27/0x40 btrfs_add_delayed_data_ref+0x3fd/0x460 btrfs_free_extent+0x42/0x100 __btrfs_mod_ref+0x1d7/0x2f0 walk_up_proc+0x11c/0x400 walk_up_tree+0xf0/0x180 btrfs_drop_snapshot+0x1c7/0x780 ? btrfs_clean_one_deleted_snapshot+0x73/0x110 btrfs_clean_one_deleted_snapshot+0xfb/0x110 cleaner_kthread+0xd4/0x140 ? btrfs_alloc_root+0x50/0x50 kthread+0x13a/0x150 ? kthread_create_worker_on_cpu+0x40/0x40 ret_from_fork+0x1f/0x30 while testing another lockdep fix. This happens because we're using the commit_root_sem to protect fs_info->caching_block_groups, which creates a dependency on the groups_sem -> commit_root_sem, which is problematic because we will allocate blocks while holding tree roots. Fix this by making the list itself protected by the fs_info->block_group_cache_lock. Reviewed-by: Filipe Manana <fdmanana@suse.com> Signed-off-by: Josef Bacik <josef@toxicpanda.com> Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
Josef Bacik
David Sterba
parent
e747853cae
commit
bbb86a3717
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@ -747,10 +747,10 @@ int btrfs_cache_block_group(struct btrfs_block_group *cache, int load_cache_only
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cache->has_caching_ctl = 1;
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spin_unlock(&cache->lock);
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down_write(&fs_info->commit_root_sem);
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spin_lock(&fs_info->block_group_cache_lock);
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refcount_inc(&caching_ctl->count);
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list_add_tail(&caching_ctl->list, &fs_info->caching_block_groups);
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up_write(&fs_info->commit_root_sem);
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spin_unlock(&fs_info->block_group_cache_lock);
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btrfs_get_block_group(cache);
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@ -999,7 +999,7 @@ int btrfs_remove_block_group(struct btrfs_trans_handle *trans,
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if (block_group->cached == BTRFS_CACHE_STARTED)
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btrfs_wait_block_group_cache_done(block_group);
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if (block_group->has_caching_ctl) {
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down_write(&fs_info->commit_root_sem);
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spin_lock(&fs_info->block_group_cache_lock);
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if (!caching_ctl) {
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struct btrfs_caching_control *ctl;
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@ -1013,7 +1013,7 @@ int btrfs_remove_block_group(struct btrfs_trans_handle *trans,
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}
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if (caching_ctl)
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list_del_init(&caching_ctl->list);
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up_write(&fs_info->commit_root_sem);
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spin_unlock(&fs_info->block_group_cache_lock);
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if (caching_ctl) {
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/* Once for the caching bgs list and once for us. */
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btrfs_put_caching_control(caching_ctl);
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@ -3311,14 +3311,14 @@ int btrfs_free_block_groups(struct btrfs_fs_info *info)
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struct btrfs_caching_control *caching_ctl;
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struct rb_node *n;
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down_write(&info->commit_root_sem);
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spin_lock(&info->block_group_cache_lock);
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while (!list_empty(&info->caching_block_groups)) {
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caching_ctl = list_entry(info->caching_block_groups.next,
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struct btrfs_caching_control, list);
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list_del(&caching_ctl->list);
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btrfs_put_caching_control(caching_ctl);
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}
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up_write(&info->commit_root_sem);
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spin_unlock(&info->block_group_cache_lock);
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spin_lock(&info->unused_bgs_lock);
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while (!list_empty(&info->unused_bgs)) {
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@ -208,6 +208,7 @@ static noinline void switch_commit_roots(struct btrfs_trans_handle *trans)
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* the caching thread will re-start it's search from 3, and thus find
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* the hole from [4,6) to add to the free space cache.
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*/
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spin_lock(&fs_info->block_group_cache_lock);
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list_for_each_entry_safe(caching_ctl, next,
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&fs_info->caching_block_groups, list) {
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struct btrfs_block_group *cache = caching_ctl->block_group;
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@ -220,6 +221,7 @@ static noinline void switch_commit_roots(struct btrfs_trans_handle *trans)
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cache->last_byte_to_unpin = caching_ctl->progress;
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}
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}
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spin_unlock(&fs_info->block_group_cache_lock);
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up_write(&fs_info->commit_root_sem);
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}
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