From: Erez Zadok <ezk@xxxxxxxxxxxxx>
Signed-off-by: Erez Zadok <ezk@xxxxxxxxxxxxx>
Signed-off-by: Josef 'Jeff' Sipek <jsipek@xxxxxxxxxxxxx>
---
fs/unionfs/inode.c | 30 ++++++++----------------------
1 files changed, 8 insertions(+), 22 deletions(-)
diff --git a/fs/unionfs/inode.c b/fs/unionfs/inode.c
index a86da5b..b5f9022 100644
--- a/fs/unionfs/inode.c
+++ b/fs/unionfs/inode.c
@@ -832,35 +832,21 @@ out:
}
/*
- * Check if dentry is valid or not, as per our generation numbers.
- * @dentry: dentry to check.
- * Returns 1 (valid) or 0 (invalid/stale).
+ * unionfs_follow_link takes a dentry, but it is simple. It only needs to
+ * allocate some memory and then call our ->readlink method. Our
+ * unionfs_readlink *does* lock our dentry and revalidate the dentry.
+ * Therefore, we do not have to lock our dentry here, to prevent a deadlock;
+ * nor do we need to revalidate it either. It is safe to not lock our
+ * dentry here, nor revalidate it, because unionfs_follow_link does not do
+ * anything (prior to calling ->readlink) which could become inconsistent
+ * due to branch management.
*/
-static inline int is_valid_dentry(struct dentry *dentry)
-{
- BUG_ON(!UNIONFS_D(dentry));
- BUG_ON(!UNIONFS_SB(dentry->d_sb));
- return (atomic_read(&UNIONFS_D(dentry)->generation) ==
- atomic_read(&UNIONFS_SB(dentry->d_sb)->generation));
-}
-
-/* We don't lock the dentry here, because readlink does the heavy lifting. */
static void *unionfs_follow_link(struct dentry *dentry, struct nameidata *nd)
{
char *buf;
int len = PAGE_SIZE, err;
mm_segment_t old_fs;
- /*
- * FIXME: Really nasty...we can get called from two distinct places:
- * 1) read_link - locks the dentry
- * 2) VFS lookup code - does NOT lock the dentry
- *
- * The proper thing would be to call dentry revalidate. It however
- * expects a locked dentry, and we can't cleanly guarantee that.
- */
- BUG_ON(!is_valid_dentry(dentry));
-
unionfs_read_lock(dentry->d_sb);
/* This is freed by the put_link method assuming a successful call. */
--
1.5.2.2.238.g7cbf2f2
-
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