vfs: do the careful dentry name access for all dentry_cmp cases
Commit 12f8ad4b0533 ("vfs: clean up __d_lookup_rcu() and dentry_cmp()
interfaces") did the careful ACCESS_ONCE() of the dentry name only for
the word-at-a-time case, even though the issue is generic.
Admittedly I don't really see gcc ever reloading the value in the middle
of the loop, so the ACCESS_ONCE() protects us from a fairly theoretical
issue. But better safe than sorry.
Also, this consolidates the common parts of the word-at-a-time and
bytewise logic, which includes checking the length. We'll be changing
that later.
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/fs/dcache.c b/fs/dcache.c
index c4d2ff8..5c09ad7 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -153,30 +153,9 @@
* In contrast, 'ct' and 'tcount' can be from a pathname, and do
* need the careful unaligned handling.
*/
-static inline int dentry_cmp(const struct dentry *dentry, const unsigned char *ct, unsigned tcount)
+static inline int dentry_string_cmp(const unsigned char *cs, const unsigned char *ct, unsigned tcount)
{
unsigned long a,b,mask;
- const unsigned char *cs;
-
- if (unlikely(dentry->d_name.len != tcount))
- return 1;
- /*
- * Be careful about RCU walk racing with rename:
- * use ACCESS_ONCE to fetch the name pointer.
- *
- * NOTE! Even if a rename will mean that the length
- * was not loaded atomically, we don't care. The
- * RCU walk will check the sequence count eventually,
- * and catch it. And we won't overrun the buffer,
- * because we're reading the name pointer atomically,
- * and a dentry name is guaranteed to be properly
- * terminated with a NUL byte.
- *
- * End result: even if 'len' is wrong, we'll exit
- * early because the data cannot match (there can
- * be no NUL in the ct/tcount data)
- */
- cs = ACCESS_ONCE(dentry->d_name.name);
for (;;) {
a = *(unsigned long *)cs;
@@ -197,13 +176,8 @@
#else
-static inline int dentry_cmp(const struct dentry *dentry, const unsigned char *ct, unsigned tcount)
+static inline int dentry_string_cmp(const unsigned char *cs, const unsigned char *ct, unsigned tcount)
{
- const unsigned char *cs = dentry->d_name.name;
-
- if (dentry->d_name.len != tcount)
- return 1;
-
do {
if (*cs != *ct)
return 1;
@@ -216,6 +190,30 @@
#endif
+static inline int dentry_cmp(const struct dentry *dentry, const unsigned char *ct, unsigned tcount)
+{
+ if (dentry->d_name.len != tcount)
+ return 1;
+
+ /*
+ * Be careful about RCU walk racing with rename:
+ * use ACCESS_ONCE to fetch the name pointer.
+ *
+ * NOTE! Even if a rename will mean that the length
+ * was not loaded atomically, we don't care. The
+ * RCU walk will check the sequence count eventually,
+ * and catch it. And we won't overrun the buffer,
+ * because we're reading the name pointer atomically,
+ * and a dentry name is guaranteed to be properly
+ * terminated with a NUL byte.
+ *
+ * End result: even if 'len' is wrong, we'll exit
+ * early because the data cannot match (there can
+ * be no NUL in the ct/tcount data)
+ */
+ return dentry_string_cmp(ACCESS_ONCE(dentry->d_name.name), ct, tcount);
+}
+
static void __d_free(struct rcu_head *head)
{
struct dentry *dentry = container_of(head, struct dentry, d_u.d_rcu);