@@ -2766,6 +2766,20 @@ static int btrfs_relocate_chunk(struct btrfs_root *root,
27662766 root = root -> fs_info -> chunk_root ;
27672767 extent_root = root -> fs_info -> extent_root ;
27682768
2769+ /*
2770+ * Prevent races with automatic removal of unused block groups.
2771+ * After we relocate and before we remove the chunk with offset
2772+ * chunk_offset, automatic removal of the block group can kick in,
2773+ * resulting in a failure when calling btrfs_remove_chunk() below.
2774+ *
2775+ * Make sure to acquire this mutex before doing a tree search (dev
2776+ * or chunk trees) to find chunks. Otherwise the cleaner kthread might
2777+ * call btrfs_remove_chunk() (through btrfs_delete_unused_bgs()) after
2778+ * we release the path used to search the chunk/dev tree and before
2779+ * the current task acquires this mutex and calls us.
2780+ */
2781+ ASSERT (mutex_is_locked (& root -> fs_info -> delete_unused_bgs_mutex ));
2782+
27692783 ret = btrfs_can_relocate (extent_root , chunk_offset );
27702784 if (ret )
27712785 return - ENOSPC ;
@@ -2814,13 +2828,18 @@ static int btrfs_relocate_sys_chunks(struct btrfs_root *root)
28142828 key .type = BTRFS_CHUNK_ITEM_KEY ;
28152829
28162830 while (1 ) {
2831+ mutex_lock (& root -> fs_info -> delete_unused_bgs_mutex );
28172832 ret = btrfs_search_slot (NULL , chunk_root , & key , path , 0 , 0 );
2818- if (ret < 0 )
2833+ if (ret < 0 ) {
2834+ mutex_unlock (& root -> fs_info -> delete_unused_bgs_mutex );
28192835 goto error ;
2836+ }
28202837 BUG_ON (ret == 0 ); /* Corruption */
28212838
28222839 ret = btrfs_previous_item (chunk_root , path , key .objectid ,
28232840 key .type );
2841+ if (ret )
2842+ mutex_unlock (& root -> fs_info -> delete_unused_bgs_mutex );
28242843 if (ret < 0 )
28252844 goto error ;
28262845 if (ret > 0 )
@@ -2843,6 +2862,7 @@ static int btrfs_relocate_sys_chunks(struct btrfs_root *root)
28432862 else
28442863 BUG_ON (ret );
28452864 }
2865+ mutex_unlock (& root -> fs_info -> delete_unused_bgs_mutex );
28462866
28472867 if (found_key .offset == 0 )
28482868 break ;
@@ -3299,9 +3319,12 @@ static int __btrfs_balance(struct btrfs_fs_info *fs_info)
32993319 goto error ;
33003320 }
33013321
3322+ mutex_lock (& fs_info -> delete_unused_bgs_mutex );
33023323 ret = btrfs_search_slot (NULL , chunk_root , & key , path , 0 , 0 );
3303- if (ret < 0 )
3324+ if (ret < 0 ) {
3325+ mutex_unlock (& fs_info -> delete_unused_bgs_mutex );
33043326 goto error ;
3327+ }
33053328
33063329 /*
33073330 * this shouldn't happen, it means the last relocate
@@ -3313,6 +3336,7 @@ static int __btrfs_balance(struct btrfs_fs_info *fs_info)
33133336 ret = btrfs_previous_item (chunk_root , path , 0 ,
33143337 BTRFS_CHUNK_ITEM_KEY );
33153338 if (ret ) {
3339+ mutex_unlock (& fs_info -> delete_unused_bgs_mutex );
33163340 ret = 0 ;
33173341 break ;
33183342 }
@@ -3321,8 +3345,10 @@ static int __btrfs_balance(struct btrfs_fs_info *fs_info)
33213345 slot = path -> slots [0 ];
33223346 btrfs_item_key_to_cpu (leaf , & found_key , slot );
33233347
3324- if (found_key .objectid != key .objectid )
3348+ if (found_key .objectid != key .objectid ) {
3349+ mutex_unlock (& fs_info -> delete_unused_bgs_mutex );
33253350 break ;
3351+ }
33263352
33273353 chunk = btrfs_item_ptr (leaf , slot , struct btrfs_chunk );
33283354
@@ -3335,10 +3361,13 @@ static int __btrfs_balance(struct btrfs_fs_info *fs_info)
33353361 ret = should_balance_chunk (chunk_root , leaf , chunk ,
33363362 found_key .offset );
33373363 btrfs_release_path (path );
3338- if (!ret )
3364+ if (!ret ) {
3365+ mutex_unlock (& fs_info -> delete_unused_bgs_mutex );
33393366 goto loop ;
3367+ }
33403368
33413369 if (counting ) {
3370+ mutex_unlock (& fs_info -> delete_unused_bgs_mutex );
33423371 spin_lock (& fs_info -> balance_lock );
33433372 bctl -> stat .expected ++ ;
33443373 spin_unlock (& fs_info -> balance_lock );
@@ -3348,6 +3377,7 @@ static int __btrfs_balance(struct btrfs_fs_info *fs_info)
33483377 ret = btrfs_relocate_chunk (chunk_root ,
33493378 found_key .objectid ,
33503379 found_key .offset );
3380+ mutex_unlock (& fs_info -> delete_unused_bgs_mutex );
33513381 if (ret && ret != - ENOSPC )
33523382 goto error ;
33533383 if (ret == - ENOSPC ) {
@@ -4087,11 +4117,16 @@ int btrfs_shrink_device(struct btrfs_device *device, u64 new_size)
40874117 key .type = BTRFS_DEV_EXTENT_KEY ;
40884118
40894119 do {
4120+ mutex_lock (& root -> fs_info -> delete_unused_bgs_mutex );
40904121 ret = btrfs_search_slot (NULL , root , & key , path , 0 , 0 );
4091- if (ret < 0 )
4122+ if (ret < 0 ) {
4123+ mutex_unlock (& root -> fs_info -> delete_unused_bgs_mutex );
40924124 goto done ;
4125+ }
40934126
40944127 ret = btrfs_previous_item (root , path , 0 , key .type );
4128+ if (ret )
4129+ mutex_unlock (& root -> fs_info -> delete_unused_bgs_mutex );
40954130 if (ret < 0 )
40964131 goto done ;
40974132 if (ret ) {
@@ -4105,6 +4140,7 @@ int btrfs_shrink_device(struct btrfs_device *device, u64 new_size)
41054140 btrfs_item_key_to_cpu (l , & key , path -> slots [0 ]);
41064141
41074142 if (key .objectid != device -> devid ) {
4143+ mutex_unlock (& root -> fs_info -> delete_unused_bgs_mutex );
41084144 btrfs_release_path (path );
41094145 break ;
41104146 }
@@ -4113,6 +4149,7 @@ int btrfs_shrink_device(struct btrfs_device *device, u64 new_size)
41134149 length = btrfs_dev_extent_length (l , dev_extent );
41144150
41154151 if (key .offset + length <= new_size ) {
4152+ mutex_unlock (& root -> fs_info -> delete_unused_bgs_mutex );
41164153 btrfs_release_path (path );
41174154 break ;
41184155 }
@@ -4122,6 +4159,7 @@ int btrfs_shrink_device(struct btrfs_device *device, u64 new_size)
41224159 btrfs_release_path (path );
41234160
41244161 ret = btrfs_relocate_chunk (root , chunk_objectid , chunk_offset );
4162+ mutex_unlock (& root -> fs_info -> delete_unused_bgs_mutex );
41254163 if (ret && ret != - ENOSPC )
41264164 goto done ;
41274165 if (ret == - ENOSPC )
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