From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from abb.hmeau.com (abb.hmeau.com [144.6.53.87]) (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 8D7F713D2B2; Sat, 3 May 2025 15:03:51 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=144.6.53.87 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1746284635; cv=none; b=qdGvl35WgVmeWnzWseEQW5OL5+vcF4kpG3koWA8N97ojbDeOi67G48lSVy8/ALTndDVvLuIbKtDGzNd9DqrwwA8rwgakfqKDEWRoJyn+Dp9mpvvuxfz0PCpOFOm6EjMhXtRfKl8Zjyre6Hb2GAQbBlJEUyeUgF9dYgdxJKl6Dus= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1746284635; c=relaxed/simple; bh=Q3jU8IweIELp/HDBkk6uZDya1bMmeBf0l/cgr0nnCNQ=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=NI5Hf2AOVo3WSGZgq66XuMbLUeinb3cNT8uZnap2f21/3BdSE6YXo6u1dEO6W1wQFz4tYKqutjwP4G4adbDtZUhn4BsprboET/tfpi4UqV9YGbZTf5KIXlyj2xwZXXkqiSXQ2TTtm5v3torIUlHiMu30l6TcpA2Nhr3b86MiuRU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=gondor.apana.org.au; spf=pass smtp.mailfrom=gondor.apana.org.au; dkim=pass (2048-bit key) header.d=hmeau.com header.i=@hmeau.com header.b=EPyF7K1p; arc=none smtp.client-ip=144.6.53.87 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=gondor.apana.org.au Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gondor.apana.org.au Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=hmeau.com header.i=@hmeau.com header.b="EPyF7K1p" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=hmeau.com; s=formenos; h=In-Reply-To:Content-Type:MIME-Version:References:Message-ID: Subject:Cc:To:From:Date:Sender:Reply-To:Content-Transfer-Encoding:Content-ID: Content-Description:Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc :Resent-Message-ID:List-Id:List-Help:List-Unsubscribe:List-Subscribe: List-Post:List-Owner:List-Archive; bh=nKPltQjGoDVIk3pbHzoFoWY2la6WaztZx7qnAjKn3N8=; b=EPyF7K1p6cu7vOUr/XV11SRuxX 7aiwUQ5Az3Atp+SbqrY4xIHYpWcrVfTshwHxizoSuhf1YyZPufpv3+LqeRXe0QrjJt8vK84GbIlmF +mv0/RkjM1H9BDZJcKXxoznb/VEQKqEaJKXdx8buuHw4sZmXpOEmIb0ytpYVkRD5VuQ/yO0VvMlrU /BRJ/xmIcmylVGlrrzU3oWm6dKpsafmMxmB34oXJGiVOMetjndtuPmIChzF/goULzg7Vqn5I13EHV XbD79L6ZpjDbpdLj2K509EfGVu4Mj97WeVaf3oSFNN0Vx7C4SXXoAJAZcn+tcIih9qbHQIADrX6Tn qIm/C5Cg==; Received: from loth.rohan.me.apana.org.au ([192.168.167.2]) by formenos.hmeau.com with smtp (Exim 4.96 #2 (Debian)) id 1uBEOH-0034vl-1y; Sat, 03 May 2025 23:02:58 +0800 Received: by loth.rohan.me.apana.org.au (sSMTP sendmail emulation); Sat, 03 May 2025 23:02:57 +0800 Date: Sat, 3 May 2025 23:02:57 +0800 From: Herbert Xu To: Jarkko Sakkinen Cc: keyrings@vger.kernel.org, David Howells , Lukas Wunner , Ignat Korchagin , "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-crypto@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: On Sat, May 03, 2025 at 05:39:16PM +0300, Jarkko Sakkinen wrote: > 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. */ You can use smp_mb__before_atomic here as it is equivalent to smp_mb in this situation. > } > 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. I don't think spin_unlock alone is enough to replace an smp_mb. A spin_lock + spin_unlock would be enough though. However, looking at the bigger picture this smp_mb looks bogus. What exactly is it protecting against? The race condition that this is supposed to fix should have been dealt with by the set_bit/test_bit of FINAL_PUT alone. I don't see any point in having this smb_mb at all. Cheers, -- Email: Herbert Xu Home Page: http://gondor.apana.org.au/~herbert/ PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt