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authorJosef Bacik <josef@redhat.com>2011-12-09 11:18:51 -0500
committerJosef Bacik <josef@redhat.com>2011-12-15 11:04:22 -0500
commit660d3f6cde552323578b85fc5a09a6742f1fe804 (patch)
tree7273af0b2a6fe7f9be685cb0586534802c807924 /fs/btrfs/relocation.c
parent22c44fe65adacd20a174f3f54686509ee94ef7be (diff)
Btrfs: fix how we do delalloc reservations and how we free reservations on error
Running xfstests 269 with some tracing my scripts kept spitting out errors about releasing bytes that we didn't actually have reserved. This took me down a huge rabbit hole and it turns out the way we deal with reserved_extents is wrong, we need to only be setting it if the reservation succeeds, otherwise the free() method will come in and unreserve space that isn't actually reserved yet, which can lead to other warnings and such. The math was all working out right in the end, but it caused all sorts of other issues in addition to making my scripts yell and scream and generally make it impossible for me to track down the original issue I was looking for. The other problem is with our error handling in the reservation code. There are two cases that we need to deal with 1) We raced with free. In this case free won't free anything because csum_bytes is modified before we dro the lock in our reservation path, so free rightly doesn't release any space because the reservation code may be depending on that reservation. However if we fail, we need the reservation side to do the free at that point since that space is no longer in use. So as it stands the code was doing this fine and it worked out, except in case #2 2) We don't race with free. Nobody comes in and changes anything, and our reservation fails. In this case we didn't reserve anything anyway and we just need to clean up csum_bytes but not free anything. So we keep track of csum_bytes before we drop the lock and if it hasn't changed we know we can just decrement csum_bytes and carry on. Because of the case where we can race with free()'s since we have to drop our spin_lock to do the reservation, I'm going to serialize all reservations with the i_mutex. We already get this for free in the heavy use paths, truncate and file write all hold the i_mutex, just needed to add it to page_mkwrite and various ioctl/balance things. With this patch my space leak scripts no longer scream bloody murder. Thanks, Signed-off-by: Josef Bacik <josef@redhat.com>
Diffstat (limited to 'fs/btrfs/relocation.c')
-rw-r--r--fs/btrfs/relocation.c2
1 files changed, 2 insertions, 0 deletions
diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
index dff29d5e151..cfb55434a46 100644
--- a/fs/btrfs/relocation.c
+++ b/fs/btrfs/relocation.c
@@ -2947,7 +2947,9 @@ static int relocate_file_extent_cluster(struct inode *inode,
index = (cluster->start - offset) >> PAGE_CACHE_SHIFT;
last_index = (cluster->end - offset) >> PAGE_CACHE_SHIFT;
while (index <= last_index) {
+ mutex_lock(&inode->i_mutex);
ret = btrfs_delalloc_reserve_metadata(inode, PAGE_CACHE_SIZE);
+ mutex_unlock(&inode->i_mutex);
if (ret)
goto out;