From 9b6a3985dc137800511d9e61d2b204592553cf68 Mon Sep 17 00:00:00 2001
From: Andreas Gruenbacher <agruenba@redhat.com>
Date: Mon, 11 Oct 2021 20:53:02 +0200
Subject: [PATCH] gfs2: Cancel remote delete work asynchronously
Git-commit: 486408d690e130c3adacf816754b97558d715f46
Patch-mainline: v5.16-rc1
References: stable-5.14.19

[ Upstream commit 486408d690e130c3adacf816754b97558d715f46 ]

In gfs2_inode_lookup and gfs2_create_inode, we're calling
gfs2_cancel_delete_work which currently cancels any remote delete work
(delete_work_func) synchronously.  This means that if the work is
currently running, it will wait for it to finish.  We're doing this to
pevent a previous instance of an inode from having any influence on the
next instance.

However, delete_work_func uses gfs2_inode_lookup internally, and we can
end up in a deadlock when delete_work_func gets interrupted at the wrong
time.  For example,

  (1) An inode's iopen glock has delete work queued, but the inode
      itself has been evicted from the inode cache.

  (2) The delete work is preempted before reaching gfs2_inode_lookup.

  (3) Another process recreates the inode (gfs2_create_inode).  It tries
      to cancel any outstanding delete work, which blocks waiting for
      the ongoing delete work to finish.

  (4) The delete work calls gfs2_inode_lookup, which blocks waiting for
      gfs2_create_inode to instantiate and unlock the new inode =>
      deadlock.

It turns out that when the delete work notices that its inode has been
re-instantiated, it will do nothing.  This means that it's safe to
cancel the delete work asynchronously.  This prevents the kind of
deadlock described above.

Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
Signed-off-by: Bob Peterson <rpeterso@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 fs/gfs2/glock.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/gfs2/glock.c b/fs/gfs2/glock.c
index 1f3902ecdded..fea68ed127b8 100644
--- a/fs/gfs2/glock.c
+++ b/fs/gfs2/glock.c
@@ -1920,7 +1920,7 @@ bool gfs2_queue_delete_work(struct gfs2_glock *gl, unsigned long delay)
 
 void gfs2_cancel_delete_work(struct gfs2_glock *gl)
 {
-	if (cancel_delayed_work_sync(&gl->gl_delete)) {
+	if (cancel_delayed_work(&gl->gl_delete)) {
 		clear_bit(GLF_PENDING_DELETE, &gl->gl_flags);
 		gfs2_glock_put(gl);
 	}
-- 
2.26.2