Re: [PATCH] Btrfs: don't ignore log btree writeback errors

["Holger Hoffstätte" <holger.hoffstaette@googlemail.com>]

On Thu, 13 Nov 2014 17:33:19 +0000, Holger Hoffstätte wrote:

> On Thu, 13 Nov 2014 16:59:53 +0000, Filipe Manana wrote:
> 
>> If an error happens during writeback of log btree extents, make sure the
>> error is returned to the caller (fsync), so that it takes proper action
>> (commit current transaction) instead of writing a superblock that points
>> to log btrees with all or some nodes that weren't durably persisted.
>> 
>> Signed-off-by: Filipe Manana <fdmanana@suse.com>
>> ---
>>  fs/btrfs/tree-log.c | 21 +++++++++++++++------
>>  1 file changed, 15 insertions(+), 6 deletions(-)
>> 
>> diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c
>> index 6d58d72..c8274d3 100644
>> --- a/fs/btrfs/tree-log.c
>> +++ b/fs/btrfs/tree-log.c
>> @@ -2599,12 +2599,14 @@ int btrfs_sync_log(struct btrfs_trans_handle *trans,
>>  	index2 = root_log_ctx.log_transid % 2;
>>  	if (atomic_read(&log_root_tree->log_commit[index2])) {
>>  		blk_finish_plug(&plug);
>> -		btrfs_wait_marked_extents(log, &log->dirty_log_pages, mark);
>> +		ret = btrfs_wait_marked_extents(log, &log->dirty_log_pages,
>> +						mark);
>>  		wait_log_commit(trans, log_root_tree,
>>  				root_log_ctx.log_transid);
>>  		btrfs_free_logged_extents(log, log_transid);
>>  		mutex_unlock(&log_root_tree->log_mutex);
>> -		ret = root_log_ctx.log_ret;
>> +		if (!ret)
>> +			ret = root_log_ctx.log_ret;
>>  		goto out;
>>  	}
>>  	ASSERT(root_log_ctx.log_transid == log_root_tree->log_transid);
> 
> This first hunk didn't apply to my 3.14.x tree that is 99.999% in sync with
> btrfs-3.18+, as a line is missing from the context. See:
> 
> https://git.kernel.org/cgit/linux/kernel/git/mason/linux-btrfs.git/tree/fs/btrfs/tree-log.c?h=for-linus#n2605
> 
> Any idea where that missing btrfs_free_logged_extents() went?

Found it: it went away with Josef's recent patch on Nov 6:
"Btrfs: make sure we wait on logged extents when fsycning two subvols"
(http://permalink.gmane.org/gmane.comp.file-systems.btrfs/40005)

..which I have applied. boohoo.

That patch also adds another call to btrfs_wait_marked_extents(), which should
then probably also have its return value handled?

thanks,
Holger