• Josef Bacik's avatar
    Btrfs: fix deadlock with nested trans handles · 3bbb24b2
    Josef Bacik authored
    Zach found this deadlock that would happen like this
    
    btrfs_end_transaction <- reduce trans->use_count to 0
      btrfs_run_delayed_refs
        btrfs_cow_block
          find_free_extent
    	btrfs_start_transaction <- increase trans->use_count to 1
              allocate chunk
    	btrfs_end_transaction <- decrease trans->use_count to 0
    	  btrfs_run_delayed_refs
    	    lock tree block we are cowing above ^^
    
    We need to only decrease trans->use_count if it is above 1, otherwise leave it
    alone.  This will make nested trans be the only ones who decrease their added
    ref, and will let us get rid of the trans->use_count++ hack if we have to commit
    the transaction.  Thanks,
    
    cc: stable@vger.kernel.org
    Reported-by: default avatarZach Brown <zab@redhat.com>
    Signed-off-by: default avatarJosef Bacik <jbacik@fb.com>
    Tested-by: default avatarZach Brown <zab@redhat.com>
    Signed-off-by: default avatarChris Mason <clm@fb.com>
    3bbb24b2
transaction.c 54.2 KB