[PATCH 1/7] shmem: shmem_charge: verify max_block is not exceeded before inode update

[Mike Rapoport]

Currently we update inode and shmem_inode_info before verifying that
used_blocks will not exceed max_blocks. In case it will, we undo the
update. Let's switch the order and move the verification of the blocks
count before the inode and shmem_inode_info update.

Signed-off-by: Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx>
---
 mm/shmem.c | 25 ++++++++++++-------------
 1 file changed, 12 insertions(+), 13 deletions(-)

diff --git a/mm/shmem.c b/mm/shmem.c
index e67d6ba..40a43ae 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -265,6 +265,14 @@ bool shmem_charge(struct inode *inode, long pages)
 
 	if (shmem_acct_block(info->flags, pages))
 		return false;
+
+	if (sbinfo->max_blocks) {
+		if (percpu_counter_compare(&sbinfo->used_blocks,
+					   sbinfo->max_blocks - pages) > 0)
+			goto unacct;
+		percpu_counter_add(&sbinfo->used_blocks, pages);
+	}
+
 	spin_lock_irqsave(&info->lock, flags);
 	info->alloced += pages;
 	inode->i_blocks += pages * BLOCKS_PER_PAGE;
@@ -272,20 +280,11 @@ bool shmem_charge(struct inode *inode, long pages)
 	spin_unlock_irqrestore(&info->lock, flags);
 	inode->i_mapping->nrpages += pages;
 
-	if (!sbinfo->max_blocks)
-		return true;
-	if (percpu_counter_compare(&sbinfo->used_blocks,
-				sbinfo->max_blocks - pages) > 0) {
-		inode->i_mapping->nrpages -= pages;
-		spin_lock_irqsave(&info->lock, flags);
-		info->alloced -= pages;
-		shmem_recalc_inode(inode);
-		spin_unlock_irqrestore(&info->lock, flags);
-		shmem_unacct_blocks(info->flags, pages);
-		return false;
-	}
-	percpu_counter_add(&sbinfo->used_blocks, pages);
 	return true;
+
+unacct:
+	shmem_unacct_blocks(info->flags, pages);
+	return false;
 }
 
 void shmem_uncharge(struct inode *inode, long pages)
-- 
2.7.4