enforce ->sync_fs is only called for rw superblock
Make sure a superblock really is writeable by checking MS_RDONLY
under s_umount. sync_filesystems needed some re-arragement for
that, but all but one sync_filesystem caller had the correct locking
already so that we could add that check there. cachefiles grew
s_umount locking.
I've also added a WARN_ON to sync_filesystem to assert this for
future callers.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/sync.c b/fs/sync.c
index 4487b55..89c37f7 100644
--- a/fs/sync.c
+++ b/fs/sync.c
@@ -51,6 +51,18 @@
{
int ret;
+ /*
+ * We need to be protected against the filesystem going from
+ * r/o to r/w or vice versa.
+ */
+ WARN_ON(!rwsem_is_locked(&sb->s_umount));
+
+ /*
+ * No point in syncing out anything if the filesystem is read-only.
+ */
+ if (sb->s_flags & MS_RDONLY)
+ return 0;
+
ret = __sync_filesystem(sb, 0);
if (ret < 0)
return ret;
@@ -79,25 +91,22 @@
mutex_lock(&mutex); /* Could be down_interruptible */
spin_lock(&sb_lock);
- list_for_each_entry(sb, &super_blocks, s_list) {
- if (sb->s_flags & MS_RDONLY)
- continue;
+ list_for_each_entry(sb, &super_blocks, s_list)
sb->s_need_sync = 1;
- }
restart:
list_for_each_entry(sb, &super_blocks, s_list) {
if (!sb->s_need_sync)
continue;
sb->s_need_sync = 0;
- if (sb->s_flags & MS_RDONLY)
- continue; /* hm. Was remounted r/o meanwhile */
sb->s_count++;
spin_unlock(&sb_lock);
+
down_read(&sb->s_umount);
- if (sb->s_root)
+ if (!(sb->s_flags & MS_RDONLY) && sb->s_root)
__sync_filesystem(sb, wait);
up_read(&sb->s_umount);
+
/* restart only when sb is no longer on the list */
spin_lock(&sb_lock);
if (__put_super_and_need_restart(sb))