Btrfs: make sure compressed bios don't complete too soon
When writing a compressed extent, a number of bios are created that
point to a single struct compressed_bio. At end_io time an atomic counter in
the compressed_bio struct makes sure that all of the bios have finished
before final end_io processing is done.
But when multiple bios are needed to write a compressed extent, the
counter was being incremented after the first bio was sent to submit_bio.
It is possible the bio will complete before the counter is incremented,
making the end_io handler free the compressed_bio struct before
processing is finished.
The fix is to increment the atomic counter before bio submission,
both for compressed reads and writes.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
diff --git a/fs/btrfs/compression.c b/fs/btrfs/compression.c
index 284f210..7397c62 100644
--- a/fs/btrfs/compression.c
+++ b/fs/btrfs/compression.c
@@ -314,6 +314,13 @@
PAGE_CACHE_SIZE) {
bio_get(bio);
+ /*
+ * inc the count before we submit the bio so
+ * we know the end IO handler won't happen before
+ * we inc the count. Otherwise, the cb might get
+ * freed before we're done setting it up
+ */
+ atomic_inc(&cb->pending_bios);
ret = btrfs_bio_wq_end_io(root->fs_info, bio, 0);
BUG_ON(ret);
@@ -323,7 +330,6 @@
bio_put(bio);
bio = compressed_bio_alloc(bdev, first_byte, GFP_NOFS);
- atomic_inc(&cb->pending_bios);
bio->bi_private = cb;
bio->bi_end_io = end_compressed_bio_write;
bio_add_page(bio, page, PAGE_CACHE_SIZE, 0);
@@ -573,6 +579,14 @@
ret = btrfs_bio_wq_end_io(root->fs_info, comp_bio, 0);
BUG_ON(ret);
+ /*
+ * inc the count before we submit the bio so
+ * we know the end IO handler won't happen before
+ * we inc the count. Otherwise, the cb might get
+ * freed before we're done setting it up
+ */
+ atomic_inc(&cb->pending_bios);
+
ret = btrfs_map_bio(root, READ, comp_bio, 0, 0);
BUG_ON(ret);
@@ -580,7 +594,6 @@
comp_bio = compressed_bio_alloc(bdev, cur_disk_byte,
GFP_NOFS);
- atomic_inc(&cb->pending_bios);
comp_bio->bi_private = cb;
comp_bio->bi_end_io = end_compressed_bio_read;