[v2,3/4] SUNRPC: no need get cache ref when protected by rcu

Commit Message

Yang Erkun Dec. 25, 2024, 6:59 a.m. UTC

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 <[e-mail]>
Signed-off-by: Yang Erkun <[e-mail]>
---
 net/sunrpc/cache.c | 12 +++---------
 1 file changed, 3 insertions(+), 9 deletions(-)

Patch

diff --git a/net/sunrpc/cache.c b/net/sunrpc/cache.c
index 88f42a27c8cc..cb279eb9ac4b 100644
--- 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);
 }