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From:   trondmy@kernel.org
To:     linux-nfs@vger.kernel.org
Subject: [PATCH] NFS: Fix a race in __nfs_list_for_each_server()
Date:   Thu, 30 Apr 2020 15:53:18 -0400
Message-Id: <20200430195318.423026-1-trondmy@kernel.org>
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From: Trond Myklebust <trond.myklebust@hammerspace.com>

The struct nfs_server gets put on the cl_superblocks list before
the server->super field has been initialised, in which case the
call to nfs_sb_active() will Oops. Add a check to ensure that
we skip such a list entry.

Fixes: 3c9e502b59fb ("NFS: Add a helper nfs_client_for_each_server()")
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
---
 fs/nfs/super.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/nfs/super.c b/fs/nfs/super.c
index 59ef3b13ccca..bdb6d0c2e755 100644
--- a/fs/nfs/super.c
+++ b/fs/nfs/super.c
@@ -185,7 +185,7 @@ static int __nfs_list_for_each_server(struct list_head *head,
 
 	rcu_read_lock();
 	list_for_each_entry_rcu(server, head, client_link) {
-		if (!nfs_sb_active(server->super))
+		if (!(server->super && nfs_sb_active(server->super)))
 			continue;
 		rcu_read_unlock();
 		if (last)
-- 
2.26.2