Miao Xie
2013-Dec-27 13:11 UTC
[PATCH 1/2] Btrfs: fix the race between write back and nocow buffered write
When we ran the 274th case of xfstests with nodatacow mount option,
We met the following warning message:
WARNING: CPU: 1 PID: 14185 at fs/btrfs/extent-tree.c:3734
btrfs_free_reserved_data_space+0xa6/0xd0
It is caused by the race between the write back and nocow buffered
write:
Task1 Task2
__btrfs_buffered_write()
skip data reservation
reserve the metadata space
copy the data
dirty the pages
unlock the pages
write back the pages
release the data space
becasue there is no
noreserve flag
set the noreserve flag
This patch fixes this problem by unlocking the pages after
the noreserve flag is set.
Reported-by: Tsutomu Itoh <t-itoh@jp.fujitsu.com>
Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
---
fs/btrfs/file.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 82d0342..f6960c2 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -1523,7 +1523,6 @@ static noinline ssize_t __btrfs_buffered_write(struct file
*file,
}
release_bytes = 0;
- btrfs_drop_pages(pages, num_pages);
if (only_release_metadata && copied > 0) {
u64 lockstart = round_down(pos, root->sectorsize);
@@ -1536,6 +1535,8 @@ static noinline ssize_t __btrfs_buffered_write(struct file
*file,
only_release_metadata = false;
}
+ btrfs_drop_pages(pages, num_pages);
+
cond_resched();
balance_dirty_pages_ratelimited(inode->i_mapping);
--
1.8.1.4
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