linux-kernel - [PATCH AUTOSEL 5.4 100/330] nfsd: Fix a soft lockup race in nfsd_file_mark_find_or

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Date:   Thu, 17 Sep 2020 21:57:20 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Trond Myklebust <trondmy@...il.com>,
        Trond Myklebust <trond.myklebust@...merspace.com>,
        "J . Bruce Fields" <bfields@...hat.com>,
        Sasha Levin <sashal@...nel.org>, linux-nfs@...r.kernel.org
Subject: [PATCH AUTOSEL 5.4 100/330] nfsd: Fix a soft lockup race in nfsd_file_mark_find_or_create()

From: Trond Myklebust <trondmy@...il.com>

[ Upstream commit 90d2f1da832fd23290ef0c0d964d97501e5e8553 ]

If nfsd_file_mark_find_or_create() keeps winning the race for the
nfsd_file_fsnotify_group->mark_mutex against nfsd_file_mark_put()
then it can soft lock up, since fsnotify_add_inode_mark() ends
up always finding an existing entry.

Signed-off-by: Trond Myklebust <trond.myklebust@...merspace.com>
Signed-off-by: J. Bruce Fields <bfields@...hat.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 fs/nfsd/filecache.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/fs/nfsd/filecache.c b/fs/nfsd/filecache.c
index 3007b8945d388..51c08ae79063c 100644
--- a/fs/nfsd/filecache.c
+++ b/fs/nfsd/filecache.c
@@ -133,9 +133,13 @@ nfsd_file_mark_find_or_create(struct nfsd_file *nf)
 						 struct nfsd_file_mark,
 						 nfm_mark));
 			mutex_unlock(&nfsd_file_fsnotify_group->mark_mutex);
-			fsnotify_put_mark(mark);
-			if (likely(nfm))
+			if (nfm) {
+				fsnotify_put_mark(mark);
 				break;
+			}
+			/* Avoid soft lockup race with nfsd_file_mark_put() */
+			fsnotify_destroy_mark(mark, nfsd_file_fsnotify_group);
+			fsnotify_put_mark(mark);
 		} else
 			mutex_unlock(&nfsd_file_fsnotify_group->mark_mutex);
 
-- 
2.25.1