linux-kernel - [PATCH] KEYS: Reduce smp_mb() calls in key

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Message-ID: <20250430152554.23646-1-jarkko@kernel.org>
Date: Wed, 30 Apr 2025 18:25:53 +0300
From: Jarkko Sakkinen <jarkko@...nel.org>
To: keyrings@...r.kernel.org
Cc: Jarkko Sakkinen <jarkko@...nel.org>,
	David Howells <dhowells@...hat.com>,
	Lukas Wunner <lukas@...ner.de>,
	Ignat Korchagin <ignat@...udflare.com>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	"David S. Miller" <davem@...emloft.net>,
	Peter Huewe <peterhuewe@....de>,
	Jason Gunthorpe <jgg@...pe.ca>,
	Paul Moore <paul@...l-moore.com>,
	James Morris <jmorris@...ei.org>,
	"Serge E. Hallyn" <serge@...lyn.com>,
	James Bottomley <James.Bottomley@...senPartnership.com>,
	Mimi Zohar <zohar@...ux.ibm.com>,
	linux-crypto@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-integrity@...r.kernel.org,
	linux-security-module@...r.kernel.org
Subject: [PATCH] KEYS: Reduce smp_mb() calls in key_put()

Rely only on the memory ordering of spin_unlock() when setting
KEY_FLAG_FINAL_PUT under key->user->lock in key_put().

Signed-off-by: Jarkko Sakkinen <jarkko@...nel.org>
---
 security/keys/key.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/security/keys/key.c b/security/keys/key.c
index 7198cd2ac3a3..aecbd624612d 100644
--- a/security/keys/key.c
+++ b/security/keys/key.c
@@ -656,10 +656,12 @@ void key_put(struct key *key)
 				spin_lock_irqsave(&key->user->lock, flags);
 				key->user->qnkeys--;
 				key->user->qnbytes -= key->quotalen;
+				set_bit(KEY_FLAG_FINAL_PUT, &key->flags);
 				spin_unlock_irqrestore(&key->user->lock, flags);
+			} else {
+				set_bit(KEY_FLAG_FINAL_PUT, &key->flags);
+				smp_mb(); /* key->user before FINAL_PUT set. */
 			}
-			smp_mb(); /* key->user before FINAL_PUT set. */
-			set_bit(KEY_FLAG_FINAL_PUT, &key->flags);
 			schedule_work(&key_gc_work);
 		}
 	}
-- 
2.47.2