From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B56C8367; Sat, 3 May 2025 14:39:21 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1746283162; cv=none; b=XT7l5ihF2Jgz6Lfvi3SIS5TRLgeu+4TX71tbbs5JaPtb1iawtwXCfM/Yqo0NVjFQ6bc+sqPbg0uCf7Vo0bLKs4lceB5XEr0Lle7daU52foDh/sVIv9H+ZbVd3TqNzMi2PE2AvnCqrRS877+TPTI/GeN39mxdmfAuZ5Y/ipbAz2Q= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1746283162; c=relaxed/simple; bh=Jr9HzCArpmz5liqhpXLnd+1v5ot8JBjFOX4E/k8pSis=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=pjksMK/Nl9HUZWnEL1DkgtVWOflR3hI3C/tmQYiPGmTfSFrTnFtjN5KmEfF2RQPzVirZApGs6JGusugP65paZVGbUgGe1QvGyt/uk8Ai4ffFGrYDpg4glxYiiZmEsDta8ssr7AejQ4MTimJuAgT2cOLM4r/2QhlcWuDHMz1TXdM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=RTr0Sjcf; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="RTr0Sjcf" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 96100C4CEE3; Sat, 3 May 2025 14:39:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1746283161; bh=Jr9HzCArpmz5liqhpXLnd+1v5ot8JBjFOX4E/k8pSis=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=RTr0SjcfzhXo8r92rzo29xHJTs63RuGBhSar+SkuDRwLHDeAi0VZKk7+ZgpwqUFW8 p7/5e32srT9aD/0JRnfyHmsepXDCGJg9pvUd6lHh39qq1CgWMg4FBYLZq9oCA+Qklo yqg0LN+h/yrQPTzo0IEmQ0v5Mu/+TrU0aFNvx2zKyzQyAMamUR9dFi0wrWgztb4tpf 1Pst1Up70ptz/Ki1YP5czDTwSPQAUIp4D8T3xw83KEGGyqTkEhqXlO2m4SOjOQ67P5 3qtyEmSBgychtj7+fW1LwO/+b2KJw3a/Uqo1sMKJzfRnDlzgdXhMnbZcXh/smTqFqm hy3e2a1WL/btQ== Date: Sat, 3 May 2025 17:39:16 +0300 From: Jarkko Sakkinen To: keyrings@vger.kernel.org Cc: David Howells , Lukas Wunner , Ignat Korchagin , Herbert Xu , "David S. Miller" , Peter Huewe , Jason Gunthorpe , Paul Moore , James Morris , "Serge E. Hallyn" , James Bottomley , Mimi Zohar , linux-crypto@vger.kernel.org, linux-kernel@vger.kernel.org, linux-integrity@vger.kernel.org, linux-security-module@vger.kernel.org Subject: Re: [PATCH] KEYS: Reduce smp_mb() calls in key_put() Message-ID: References: <20250430152554.23646-1-jarkko@kernel.org> Precedence: bulk X-Mailing-List: linux-security-module@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250430152554.23646-1-jarkko@kernel.org> On Wed, Apr 30, 2025 at 06:25:53PM +0300, Jarkko Sakkinen wrote: > 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 > --- > 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