Re: [PATCH] KEYS: Reduce smp_mb() calls in key_put()
From: Jarkko Sakkinen <jarkko@kernel.org>
Date: 2025-05-03 14:39:21
Also in:
keyrings, linux-crypto, linux-integrity, lkml
On Wed, Apr 30, 2025 at 06:25:53PM +0300, Jarkko Sakkinen wrote:
quoted hunk ↗ jump to hunk
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@kernel.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);
Oops, my bad (order swap), sorry. Should have been:
spin_unlock_irqrestore(&key->user->lock, flags);
} else {
smp_mb(); /* key->user before FINAL_PUT set. */
}
set_bit(KEY_FLAG_FINAL_PUT, &key->flags);
Should spin_lock()/unlock() be good enough or what good does smp_mb() do
in that branch? Just checking if I'm missing something before sending
fixed version.
BR, Jarkko