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Btrfs: wake up extent state waiters on unlock through clear_extent_bits

PATCH In review Filipe Manana 2 participants 2 messages May 14, 2015 – May 18, 2015 Btrfs file system

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Filipe Manana

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PATCH 1/1 Btrfs: wake up extent state waiters on unlock through clear_extent_bits

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 <[email protected]>
Signed-off-by Filipe Manana <[email protected]>
---
 fs/btrfs/extent_io.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)
fs/btrfs/extent_io.c +6 -1
index c32d226..856c2e8 100644
@@ -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,
Signature · 1 line
2.1.3
Reviewed-by on v1 1/1
#1 lore raw
Quoted 9 lines · 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.

Good catch!

Reviewed-by Liu Bo <[email protected]>

Thanks,

-liubo

Quoted 32 lines
Reported-by Zygo Blaxell <[email protected]>
Signed-off-by Filipe Manana <[email protected]>
---
 fs/btrfs/extent_io.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)
fs/btrfs/extent_io.c +6 -1
index c32d226..856c2e8 100644
@@ -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,
Signature · 6 lines
2.1.3

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