autofs4: fix pending checks

There are two cases for which a dentry that has a pending mount request
does not wait for completion.  One is via autofs4_revalidate() and the
other via autofs4_follow_link().

In revalidate, after the mount point directory is created, but before the
mount is done, the check in try_to_fill_dentry() can can fail to send the
dentry to the wait queue since the dentry is positive and the lookup flags
may contain only LOOKUP_FOLLOW.  Although we don't trigger a mount for the
LOOKUP_FOLLOW flag, if ther's one pending we might as well wait and use
the mounted dentry for the lookup.

In autofs4_follow_link() the dentry is not checked to see if it is pending
so it may fail to call try_to_fill_dentry() and not wait for mount
completion.

A dentry that is pending must always be sent to the wait queue.

Signed-off-by: Ian Kent <raven@themaw.net>
Reviewed-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 6 insertions, 3 deletions

diff --git a/fs/autofs4/root.c b/fs/autofs4/root.c
index 51c873ca8e8d..61d1dca16884 100644
--- a/fs/autofs4/root.c
+++ b/fs/autofs4/root.c
@@ -177,7 +177,8 @@ static int try_to_fill_dentry(struct dentry *dentry, int flags)
                         return status;
                 }
         /* Trigger mount for path component or follow link */
-        } else if (flags & (TRIGGER_FLAGS | TRIGGER_INTENTS) ||
+        } else if (dentry->d_flags & DCACHE_AUTOFS_PENDING ||
+                        flags & (TRIGGER_FLAGS | TRIGGER_INTENTS) ||
                         current->link_count) {
                 DPRINTK("waiting for mount name=%.*s",
                         dentry->d_name.len, dentry->d_name.name);
@@ -223,7 +224,8 @@ static void *autofs4_follow_link(struct dentry *dentry, struct nameidata *nd)
 
         /* If it's our master or we shouldn't trigger a mount we're done */
         lookup_type = nd->flags & (TRIGGER_FLAGS | TRIGGER_INTENTS);
-        if (oz_mode || !lookup_type)
+        if (oz_mode ||
+            !(lookup_type || dentry->d_flags & DCACHE_AUTOFS_PENDING))
                 goto done;
 
         /* If an expire request is pending wait for it. */
@@ -242,7 +244,8 @@ static void *autofs4_follow_link(struct dentry *dentry, struct nameidata *nd)
          * don't try to mount it again.
          */
         spin_lock(&dcache_lock);
-        if (!d_mountpoint(dentry) && __simple_empty(dentry)) {
+        if (dentry->d_flags & DCACHE_AUTOFS_PENDING ||
+            (!d_mountpoint(dentry) && __simple_empty(dentry))) {
                 spin_unlock(&dcache_lock);
 
                 status = try_to_fill_dentry(dentry, 0);