gfs2: Smarter iopen glock waiting

When trying to upgrade the iopen glock from a shared to an exclusive lock in
gfs2_evict_inode, abort the wait if there is contention on the corresponding
inode glock: in that case, the inode must still be in active use on another
node, and we're not guaranteed to get the iopen glock anytime soon.

To make this work even better, when we notice contention on the iopen glock and
we can't evict the corresponsing inode and release the iopen glock immediately,
poke the inode glock.  The other node(s) trying to acquire the lock can then
abort instead of timing out.

Thanks to Heinz Mauelshagen for pointing out a locking bug in a previous
version of this patch.

Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>

1 files changed, 8 insertions, 3 deletions

diff --git a/fs/gfs2/super.c b/fs/gfs2/super.c
index bcb56f13f50a..32d8d26126a1 100644
--- a/fs/gfs2/super.c
+++ b/fs/gfs2/super.c
@@ -1273,8 +1273,12 @@ static bool gfs2_upgrade_iopen_glock(struct inode *inode)
 	 * If there are no other lock holders, we'll get the lock immediately.
 	 * Otherwise, the other nodes holding the lock will be notified about
 	 * our locking request.  If they don't have the inode open, they'll
-	 * evict the cached inode and release the lock.  As a last resort,
-	 * we'll eventually time out.
+	 * evict the cached inode and release the lock.  Otherwise, if they
+	 * poke the inode glock, we'll take this as an indication that they
+	 * still need the iopen glock and that they'll take care of deleting
+	 * the inode when they're done.  As a last resort, if another node
+	 * keeps holding the iopen glock without showing any activity on the
+	 * inode glock, we'll eventually time out.
 	 *
 	 * Note that we're passing the LM_FLAG_TRY_1CB flag to the first
 	 * locking request as an optimization to notify lock holders as soon as
@@ -1293,7 +1297,8 @@ static bool gfs2_upgrade_iopen_glock(struct inode *inode)
 		return false;
 
 	timeout = wait_event_interruptible_timeout(sdp->sd_async_glock_wait,
-		!test_bit(HIF_WAIT, &gh->gh_iflags),
+		!test_bit(HIF_WAIT, &gh->gh_iflags) ||
+		test_bit(GLF_DEMOTE, &ip->i_gl->gl_flags),
 		timeout);
 	if (!test_bit(HIF_HOLDER, &gh->gh_iflags)) {
 		gfs2_glock_dq(gh);