[PATCH] mm/shmem: Fix invalid PTR_ERR(NULL) call in shmem_xattr_handler_set()

[Qasim Ijaz <qasdev00@gmail.com>]

In shmem_xattr_handler_set() if simple_xattr_set() succeeds and the pointer
returned is not an error pointer, then old_xattr will be set to NULL in
the body of the following if statement:

    if (!IS_ERR(old_xattr))

Later on shmem_xattr_handler_set() calls:

    return PTR_ERR(old_xattr);

The PTR_ERR macro is used to extract an error code from an error pointer
and NULL is not an error pointer, PTR_ERR(NULL) simply results in 0.

To improve correctness and readability, refactor the error handling 
to have an explicit default return value of 0 (success) in "ret". 
If simple_xattr_set() returns an error pointer, store its 
error code in "ret".

Signed-off-by: Qasim Ijaz <qasdev00@gmail.com>
---
 mm/shmem.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/mm/shmem.c b/mm/shmem.c
index 532afd8e049c..3e97c7890aac 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -4143,6 +4143,7 @@ static int shmem_xattr_handler_set(const struct xattr_handler *handler,
 	struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);
 	struct simple_xattr *old_xattr;
 	size_t ispace = 0;
+	int ret = 0;
 
 	name = xattr_full_name(handler, name);
 	if (value && sbinfo->max_inodes) {
@@ -4158,7 +4156,9 @@ static int shmem_xattr_handler_set(const struct xattr_handler *handler,
 	}
 
 	old_xattr = simple_xattr_set(&info->xattrs, name, value, size, flags);
-	if (!IS_ERR(old_xattr)) {
+	if (IS_ERR(old_xattr)) {
+		ret = PTR_ERR(old_xattr);
+	} else {
 		ispace = 0;
 		if (old_xattr && sbinfo->max_inodes)
 			ispace = simple_xattr_space(old_xattr->name,
@@ -4168,12 +4171,13 @@ static int shmem_xattr_handler_set(const struct xattr_handler *handler,
 		inode_set_ctime_current(inode);
 		inode_inc_iversion(inode);
 	}
+
 	if (ispace) {
 		raw_spin_lock(&sbinfo->stat_lock);
 		sbinfo->free_ispace += ispace;
 		raw_spin_unlock(&sbinfo->stat_lock);
 	}
-	return PTR_ERR(old_xattr);
+	return ret;
 }
 
 static const struct xattr_handler shmem_security_xattr_handler = {
-- 
2.39.5