Coverity: read_one_block_group(): Concurrent data access violations

[coverity-bot <keescook@chromium.org>]

Hello!

This is an experimental automated report about issues detected by Coverity
from a scan of next-20191108 as part of the linux-next weekly scan project:
https://scan.coverity.com/projects/linux-next-weekly-scan

You're getting this email because you were associated with the identified
lines of code (noted below) that were touched by recent commits:

593669fa8fd7 ("btrfs: block-group: Refactor btrfs_read_block_groups()")

Coverity reported the following:

*** CID 1487834:  Concurrent data access violations  (MISSING_LOCK)
/fs/btrfs/block-group.c: 1721 in read_one_block_group()
1715     		 *    truncate the old free space cache inode and
1716     		 *    setup a new one.
1717     		 * b) Setting 'dirty flag' makes sure that we flush
1718     		 *    the new space cache info onto disk.
1719     		 */
1720     		if (btrfs_test_opt(info, SPACE_CACHE))
vvv     CID 1487834:  Concurrent data access violations  (MISSING_LOCK)
vvv     Accessing "cache->disk_cache_state" without holding lock "btrfs_block_group_cache.lock". Elsewhere, "btrfs_block_group_cache.disk_cache_state" is accessed with "btrfs_block_group_cache.lock" held 12 out of 13 times (6 of these accesses strongly imply that it is necessary).
1721     			cache->disk_cache_state = BTRFS_DC_CLEAR;
1722     	}
1723     	read_extent_buffer(leaf, &bgi, btrfs_item_ptr_offset(leaf, slot),
1724     			   sizeof(bgi));
1725     	if (!mixed && ((cache->flags & BTRFS_BLOCK_GROUP_METADATA) &&
1726     	    (cache->flags & BTRFS_BLOCK_GROUP_DATA))) {

If this is a false positive, please let us know so we can mark it as
such, or teach the Coverity rules to be smarter. If not, please make
sure fixes get into linux-next. :) For patches fixing this, please
include these lines (but double-check the "Fixes" first):

Reported-by: coverity-bot <keescook+coverity-bot@chromium.org>
Addresses-Coverity-ID: 1487834 ("Concurrent data access violations")
Fixes: 593669fa8fd7 ("btrfs: block-group: Refactor btrfs_read_block_groups()")


Thanks for your attention!

-- 
Coverity-bot