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23 October 2021, 00:29:24 UTC
Revision 758f2dfcf8a249b1f1510aa32e625c2ec20642a3 authored by Filipe Manana on 19 November 2015, 11:45:48 UTC, committed by Chris Mason on 25 November 2015, 13:22:08 UTC 
Btrfs: fix scrub preventing unused block groups from being deleted
 
Currently scrub can race with the cleaner kthread when the later attempts
to delete an unused block group, and the result is preventing the cleaner
kthread from ever deleting later the block group - unless the block group
becomes used and unused again. The following diagram illustrates that
race:

              CPU 1                                 CPU 2

 cleaner kthread
   btrfs_delete_unused_bgs()

     gets block group X from
     fs_info->unused_bgs and
     removes it from that list

                                             scrub_enumerate_chunks()

                                               searches device tree using
                                               its commit root

                                               finds device extent for
                                               block group X

                                               gets block group X from the tree
                                               fs_info->block_group_cache_tree
                                               (via btrfs_lookup_block_group())

                                               sets bg X to RO

     sees the block group is
     already RO and therefore
     doesn't delete it nor adds
     it back to unused list

So fix this by making scrub add the block group again to the list of
unused block groups if the block group is still unused when it finished
scrubbing it and it hasn't been removed already.

Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Chris Mason <clm@fb.com>
1 parent 020d5b7
Raw File
Tip revision: 758f2dfcf8a249b1f1510aa32e625c2ec20642a3 authored by Filipe Manana on 19 November 2015, 11:45:48 UTC
Btrfs: fix scrub preventing unused block groups from being deleted
Tip revision: 758f2df
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