[PATCH] Btrfs: wake up extent state waiters on unlock through clear_extent_bits

[PATCH] Btrfs: wake up extent state waiters on unlock through clear_extent_bits

[Filipe Manana]

When we clear an extent state's EXTENT_LOCKED bit with clear_extent_bits()
through free_io_failure(), we weren't waking up any tasks waiting for the
extent's state EXTENT_LOCKED bit, leading to an hang.

So make sure clear_extent_bits() ends up waking up any waiters if the
bit EXTENT_LOCKED is supplied by its callers.

Zygo Blaxell was experiencing such hangs at inode eviction time after
file unlinks. Thanks to him for a set of scripts to reproduce the issue.

Reported-by: Zygo Blaxell <ce3g8jdj@umail.furryterror.org>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
---
 fs/btrfs/extent_io.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index c32d226..856c2e8 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -1277,7 +1277,12 @@ int set_extent_bits(struct extent_io_tree *tree, u64 start, u64 end,
 int clear_extent_bits(struct extent_io_tree *tree, u64 start, u64 end,
 		      unsigned bits, gfp_t mask)
 {
-	return clear_extent_bit(tree, start, end, bits, 0, 0, NULL, mask);
+	int wake = 0;
+
+	if (bits & EXTENT_LOCKED)
+		wake = 1;
+
+	return clear_extent_bit(tree, start, end, bits, wake, 0, NULL, mask);
 }
 
 int set_extent_delalloc(struct extent_io_tree *tree, u64 start, u64 end,
-- 
2.1.3

Re: [PATCH] Btrfs: wake up extent state waiters on unlock through clear_extent_bits

[Liu Bo]

On Thu, May 14, 2015 at 08:41:07PM +0100, Filipe Manana wrote:
> When we clear an extent state's EXTENT_LOCKED bit with clear_extent_bits()
> through free_io_failure(), we weren't waking up any tasks waiting for the
> extent's state EXTENT_LOCKED bit, leading to an hang.
> 
> So make sure clear_extent_bits() ends up waking up any waiters if the
> bit EXTENT_LOCKED is supplied by its callers.
> 
> Zygo Blaxell was experiencing such hangs at inode eviction time after
> file unlinks. Thanks to him for a set of scripts to reproduce the issue.

Good catch!

Reviewed-by: Liu Bo <bo.li.liu@oracle.com>

Thanks,

-liubo

> 
> Reported-by: Zygo Blaxell <ce3g8jdj@umail.furryterror.org>
> Signed-off-by: Filipe Manana <fdmanana@suse.com>
> ---
>  fs/btrfs/extent_io.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
> index c32d226..856c2e8 100644
> --- a/fs/btrfs/extent_io.c
> +++ b/fs/btrfs/extent_io.c
> @@ -1277,7 +1277,12 @@ int set_extent_bits(struct extent_io_tree *tree, u64 start, u64 end,
>  int clear_extent_bits(struct extent_io_tree *tree, u64 start, u64 end,
>  		      unsigned bits, gfp_t mask)
>  {
> -	return clear_extent_bit(tree, start, end, bits, 0, 0, NULL, mask);
> +	int wake = 0;
> +
> +	if (bits & EXTENT_LOCKED)
> +		wake = 1;
> +
> +	return clear_extent_bit(tree, start, end, bits, wake, 0, NULL, mask);
>  }
>  
>  int set_extent_delalloc(struct extent_io_tree *tree, u64 start, u64 end,
> -- 
> 2.1.3
> 
> --
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