• Filipe Manana's avatar
    Btrfs: fix access to available allocation bits when starting balance · 5a8067c0
    Filipe Manana authored
    The available allocation bits members from struct btrfs_fs_info are
    protected by a sequence lock, and when starting balance we access them
    incorrectly in two different ways:
    
    1) In the read sequence lock loop at btrfs_balance() we use the values we
       read from fs_info->avail_*_alloc_bits and we can immediately do actions
       that have side effects and can not be undone (printing a message and
       jumping to a label). This is wrong because a retry might be needed, so
       our actions must not have side effects and must be repeatable as long
       as read_seqretry() returns a non-zero value. In other words, we were
       essentially ignoring the sequence lock;
    
    2) Right below the read sequence lock loop, we were reading the values
       from avail_metadata_alloc_bits and avail_data_alloc_bits without any
       protection from concurrent writers, that is, reading them outside of
       the read sequence lock critical section.
    
    So fix this by making sure we only read the available allocation bits
    while in a read sequence lock critical section and that what we do in the
    critical section is repeatable (has nothing that can not be undone) so
    that any eventual retry that is needed is handled properly.
    
    Fixes: de98ced9 ("Btrfs: use seqlock to protect fs_info->avail_{data, metadata, system}_alloc_bits")
    Fixes: 14506127 ("btrfs: fix a bogus warning when converting only data or metadata")
    Reviewed-by: default avatarNikolay Borisov <nborisov@suse.com>
    Signed-off-by: default avatarFilipe Manana <fdmanana@suse.com>
    Reviewed-by: default avatarDavid Sterba <dsterba@suse.com>
    Signed-off-by: default avatarDavid Sterba <dsterba@suse.com>
    5a8067c0
volumes.c 206 KB