SUNRPC: no need get cache ref when protected by rcu

rcu_read_lock/rcu_read_unlock has already provide protection for the
pointer we will reference when we call c_show. Therefore, there is no
need to obtain a cache reference to help protect cache_head.
Additionally, the .put such as expkey_put/svc_export_put will invoke
dput, which can sleep and break rcu. Stop get cache reference to fix
them all.

Fixes: ae74136b4bb6 ("SUNRPC: Allow cache lookups to use RCU protection rather than the r/w spinlock")
Suggested-by: NeilBrown <neilb@suse.de>
Signed-off-by: Yang Erkun <yangerkun@huawei.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

diff --git a/net/sunrpc/cache.c b/net/sunrpc/cache.c
index 88f42a27c8cc92db41c1a1f9e252b7eeb5ca520c..cb279eb9ac4ba54b59417515de08dd3ff686e0e9 100644 (file)
--- a/net/sunrpc/cache.c
+++ b/net/sunrpc/cache.c
@@ -1438,17 +1438,11 @@ static int c_show(struct seq_file *m, void *p)
                seq_printf(m, "# expiry=%lld refcnt=%d flags=%lx\n",
                           convert_to_wallclock(cp->expiry_time),
                           kref_read(&cp->ref), cp->flags);
-       if (!cache_get_rcu(cp))
-               return 0;
 
-       if (cache_check(cd, cp, NULL))
-               /* cache_check does a cache_put on failure */
+       if (cache_check_rcu(cd, cp, NULL))
+               seq_puts(m, "# ");
+       else if (cache_is_expired(cd, cp))
                seq_puts(m, "# ");
-       else {
-               if (cache_is_expired(cd, cp))
-                       seq_puts(m, "# ");
-               cache_put(cp, cd);
-       }
 
        return cd->cache_show(m, cd, cp);
 }