[PATCH] ocfs2: fix cached cluster count after suballocator reclaim

[Matthias Goergens <matthias.goergens@gmail.com>]

When reclaiming a suballocator block group, first reduce the on-disk
cluster count by cl_cpg.  The current code then subtracts that new count
from the old cached count.

For an allocator with N groups, that leaves the cache at

    N * cl_cpg - (N - 1) * cl_cpg = cl_cpg

regardless of N.  This happens to be correct when reclaiming from two
groups, but undercounts the clusters from three groups onwards.  The
incorrect cache value is also used immediately to update i_blocks.

Assign the updated on-disk count to the cache, matching the allocation and
inode refresh paths.

In a QEMU test using a clean 256 MiB OCFS2 image and a 10,000-file
create/delete workload, the first buggy reclaim left the on-disk and cached
counts at 2048 and 512 clusters respectively; later reclaims underflowed
the cache.  With this change, the cache matched the on-disk count across
all four reclaims: 2048, 1536, 1024, and 512 clusters.

Fixes: 4a54331616b3 ("ocfs2: give ocfs2 the ability to reclaim suballocator free bg")
Cc: stable@vger.kernel.org
Signed-off-by: Matthias Goergens <matthias.goergens@gmail.com>
---
 fs/ocfs2/suballoc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/ocfs2/suballoc.c b/fs/ocfs2/suballoc.c
index a4a2b87a45fe3..20c3aec6b9873 100644
--- a/fs/ocfs2/suballoc.c
+++ b/fs/ocfs2/suballoc.c
@@ -2759,7 +2759,7 @@ static int _ocfs2_reclaim_suballoc_to_main(handle_t *handle,
 	fe->i_clusters = cpu_to_le32(tmp_used - le16_to_cpu(cl->cl_cpg));
 
 	spin_lock(&OCFS2_I(alloc_inode)->ip_lock);
-	OCFS2_I(alloc_inode)->ip_clusters -= le32_to_cpu(fe->i_clusters);
+	OCFS2_I(alloc_inode)->ip_clusters = le32_to_cpu(fe->i_clusters);
 	fe->i_size = cpu_to_le64(ocfs2_clusters_to_bytes(alloc_inode->i_sb,
 					     le32_to_cpu(fe->i_clusters)));
 	spin_unlock(&OCFS2_I(alloc_inode)->ip_lock);
-- 
2.55.0