linux-kernel - [PATCH 5.9 231/255] NFSv4.2: fix failure to unregister shrinker

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Date:   Tue, 17 Nov 2020 14:06:11 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Kris Karas <bugs-a17@...nlit-rail.com>,
        "J. Bruce Fields" <bfields@...hat.com>,
        Anna Schumaker <Anna.Schumaker@...app.com>
Subject: [PATCH 5.9 231/255] NFSv4.2: fix failure to unregister shrinker

From: J. Bruce Fields <bfields@...hat.com>

commit 70438afbf17e5194dd607dd17759560a363b7bb4 upstream.

We forgot to unregister the nfs4_xattr_large_entry_shrinker.

That leaves the global list of shrinkers corrupted after unload of the
nfs module, after which possibly unrelated code that calls
register_shrinker() or unregister_shrinker() gets a BUG() with
"supervisor write access in kernel mode".

And similarly for the nfs4_xattr_large_entry_lru.

Reported-by: Kris Karas <bugs-a17@...nlit-rail.com>
Tested-By: Kris Karas <bugs-a17@...nlit-rail.com>
Fixes: 95ad37f90c33 "NFSv4.2: add client side xattr caching."
Signed-off-by: J. Bruce Fields <bfields@...hat.com>
CC: stable@...r.kernel.org
Signed-off-by: Anna Schumaker <Anna.Schumaker@...app.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 fs/nfs/nfs42xattr.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/fs/nfs/nfs42xattr.c
+++ b/fs/nfs/nfs42xattr.c
@@ -1048,8 +1048,10 @@ out4:

 void nfs4_xattr_cache_exit(void)
 {
+	unregister_shrinker(&nfs4_xattr_large_entry_shrinker);
 	unregister_shrinker(&nfs4_xattr_entry_shrinker);
 	unregister_shrinker(&nfs4_xattr_cache_shrinker);
+	list_lru_destroy(&nfs4_xattr_large_entry_lru);
 	list_lru_destroy(&nfs4_xattr_entry_lru);
 	list_lru_destroy(&nfs4_xattr_cache_lru);
 	kmem_cache_destroy(nfs4_xattr_cache_cachep);