On Thu 21-01-16 10:46:01, Ross Zwisler wrote:
> Previously in dax_writeback_one() we cleared the PAGECACHE_TAG_TOWRITE flag
> before we had actually flushed the tagged radix tree entry to media. This
> is incorrect because of the following race:
>
> Thread 1 Thread 2
> -------- --------
> dax_writeback_mapping_range()
> tag entry with PAGECACHE_TAG_TOWRITE
> dax_writeback_mapping_range()
> tag entry with PAGECACHE_TAG_TOWRITE
> dax_writeback_one()
> radix_tree_tag_clear(TOWRITE)
> TOWRITE flag is no longer set,
> find_get_entries_tag() finds no
> entries, return
> flush entry to media
>
> In this case thread 1 returns before the data for the dirty entry is
> actually durable on media.
>
> Fix this by only clearing the PAGECACHE_TAG_TOWRITE flag after all flushing
> is complete.
>
> Signed-off-by: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
> Reported-by: Jan Kara <jack@xxxxxxx>
Looks good. You can add:
Reviewed-by: Jan Kara <jack@xxxxxxx>
Honza
> ---
> fs/dax.c | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/fs/dax.c b/fs/dax.c
> index cee9e1b..d589113 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -407,8 +407,6 @@ static int dax_writeback_one(struct block_device *bdev,
> if (!radix_tree_tag_get(page_tree, index, PAGECACHE_TAG_TOWRITE))
> goto unlock;
>
> - radix_tree_tag_clear(page_tree, index, PAGECACHE_TAG_TOWRITE);
> -
> if (WARN_ON_ONCE(type != RADIX_DAX_PTE && type != RADIX_DAX_PMD)) {
> ret = -EIO;
> goto unlock;
> @@ -432,6 +430,10 @@ static int dax_writeback_one(struct block_device *bdev,
> }
>
> wb_cache_pmem(dax.addr, dax.size);
> +
> + spin_lock_irq(&mapping->tree_lock);
> + radix_tree_tag_clear(page_tree, index, PAGECACHE_TAG_TOWRITE);
> + spin_unlock_irq(&mapping->tree_lock);
> unmap:
> dax_unmap_atomic(bdev, &dax);
> return ret;
> --
> 2.5.0
>
>
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
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