cifs: fix potential races in cifs_revalidate_mapping
The handling of the CIFS_INO_INVALID_MAPPING flag is racy. It's possible
for two tasks to attempt to revalidate the mapping at the same time. The
first sees that CIFS_INO_INVALID_MAPPING is set. It clears the flag and
then calls invalidate_inode_pages2 to start shooting down the pagecache.
While that's going on, another task checks the flag and sees that it's
clear. It then ends up trusting the pagecache to satisfy a read when it
shouldn't.
Fix this by adding a bitlock to ensure that the clearing of the flag is
atomic with respect to the actual cache invalidation. Also, move the
other existing users of cifs_invalidate_mapping to use a new
cifs_zap_mapping() function that just sets the INVALID_MAPPING bit and
then uses the standard codepath to handle the invalidation.
Signed-off-by: Jeff Layton <jlayton@poochiereds.net>
Signed-off-by: Steve French <smfrench@gmail.com>
diff --git a/fs/cifs/inode.c b/fs/cifs/inode.c
index ff420b2..9ff8df8b 100644
--- a/fs/cifs/inode.c
+++ b/fs/cifs/inode.c
@@ -22,6 +22,7 @@
#include <linux/stat.h>
#include <linux/slab.h>
#include <linux/pagemap.h>
+#include <linux/freezer.h>
#include <asm/div64.h>
#include "cifsfs.h"
#include "cifspdu.h"
@@ -1762,29 +1763,60 @@
cifs_invalidate_mapping(struct inode *inode)
{
int rc = 0;
- struct cifsInodeInfo *cifs_i = CIFS_I(inode);
-
- clear_bit(CIFS_INO_INVALID_MAPPING, &cifs_i->flags);
if (inode->i_mapping && inode->i_mapping->nrpages != 0) {
rc = invalidate_inode_pages2(inode->i_mapping);
- if (rc) {
+ if (rc)
cifs_dbg(VFS, "%s: could not invalidate inode %p\n",
__func__, inode);
- set_bit(CIFS_INO_INVALID_MAPPING, &cifs_i->flags);
- }
}
cifs_fscache_reset_inode_cookie(inode);
return rc;
}
+/**
+ * cifs_wait_bit_killable - helper for functions that are sleeping on bit locks
+ * @word: long word containing the bit lock
+ */
+static int
+cifs_wait_bit_killable(void *word)
+{
+ if (fatal_signal_pending(current))
+ return -ERESTARTSYS;
+ freezable_schedule_unsafe();
+ return 0;
+}
+
int
cifs_revalidate_mapping(struct inode *inode)
{
- if (test_bit(CIFS_INO_INVALID_MAPPING, &CIFS_I(inode)->flags))
- return cifs_invalidate_mapping(inode);
- return 0;
+ int rc;
+ unsigned long *flags = &CIFS_I(inode)->flags;
+
+ rc = wait_on_bit_lock(flags, CIFS_INO_LOCK, cifs_wait_bit_killable,
+ TASK_KILLABLE);
+ if (rc)
+ return rc;
+
+ if (test_and_clear_bit(CIFS_INO_INVALID_MAPPING, flags)) {
+ rc = cifs_invalidate_mapping(inode);
+ if (rc)
+ set_bit(CIFS_INO_INVALID_MAPPING, flags);
+ }
+
+ clear_bit_unlock(CIFS_INO_LOCK, flags);
+ smp_mb__after_clear_bit();
+ wake_up_bit(flags, CIFS_INO_LOCK);
+
+ return rc;
+}
+
+int
+cifs_zap_mapping(struct inode *inode)
+{
+ set_bit(CIFS_INO_INVALID_MAPPING, &CIFS_I(inode)->flags);
+ return cifs_revalidate_mapping(inode);
}
int cifs_revalidate_file_attr(struct file *filp)