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 43B492F5A34; Tue, 31 Mar 2026 00:46:30 +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=1774917990; cv=none; b=p698pHzGJN3Xp43BGa4XvKo+t232qt+j9Mux1kEnc1VUSZI/CF/EHZD4ygeBhAQDHzX5fknNrXViI7Uzm80FtWDTl16a9dRu4+h5TRI0eQMzDCjF4iriBS9Ed5yqUZEY++uptRPXwzA8Of3Cx/sjI+a6SMtzJcGaXb/ioXRPbUg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774917990; c=relaxed/simple; bh=Ng5xulmJbykg7qv1WJ/ziJTsz9xWAcA5AbewZsttxPQ=; h=Date:From:To:Cc:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=eKaYAgoetcaCF9o6Pzog+2SKpgu2wxjlD1KXlcj+bIsKwNO0XY5zU3DEEQoNXF8rf6ImMTmS9Luz5aW90B4htTsM6DAvpfi9vUuRprUwPFJu0wT3jqM6agHxVsHfO6SRHwEFBtVcrPIZw+nRosTWrPeJe6nd6auicJinort3Wpw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=WkSRGqPw; 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="WkSRGqPw" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6DC70C4CEF7; Tue, 31 Mar 2026 00:46:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1774917989; bh=Ng5xulmJbykg7qv1WJ/ziJTsz9xWAcA5AbewZsttxPQ=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=WkSRGqPwi79zR2IIYC0RU40bAtDsfM3TMLoKocwUFShNZ3HuuILAAjxU8KlgY7EoI 6Xz/gLlapPA0UDiAwoe9+esZUOrSxLOI/Rkp42AAE2q8O84tYAaotKdavS+URQmw7D gU/oFQ2L+KdVD/8o7R7vFzl2SkglzUt44oBDcLmwreyF/4rNBlYp4TUQXICo9lnDRj EJk6OikG30dMZfF2vwe+WuY1hi1Bi7cpglmDYf9g4DGTxLEJeVRYuPqKJdbdYOI5W0 ca45mNzFzrM7wyel9mH7RMIWXIYJRsozLukYp2boCNxvIBaiRn/j9ia2EMx858QFfL E5xRkd56GLEwQ== Date: Mon, 30 Mar 2026 17:46:28 -0700 From: Jakub Kicinski To: Hangbin Liu Cc: "David S. Miller" , David Ahern , Eric Dumazet , Paolo Abeni , Simon Horman , Jiayuan Chen , David Ahern , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Fei Liu Subject: Re: [PATCH net v2] ipv6: fix data race in fib6_metric_set() using cmpxchg Message-ID: <20260330174628.0cb1ebc6@kernel.org> In-Reply-To: <20260327-b4-fib6_metric_set-kmemleak-v2-1-366b2c78b5c2@gmail.com> References: <20260327-b4-fib6_metric_set-kmemleak-v2-1-366b2c78b5c2@gmail.com> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Fri, 27 Mar 2026 10:24:47 +0800 Hangbin Liu wrote: > --- a/net/ipv6/ip6_fib.c > +++ b/net/ipv6/ip6_fib.c > @@ -730,17 +730,24 @@ void fib6_metric_set(struct fib6_info *f6i, int metric, u32 val) > if (!f6i) > return; > > - if (f6i->fib6_metrics == &dst_default_metrics) { > + if (READ_ONCE(f6i->fib6_metrics) == &dst_default_metrics) { > + struct dst_metrics *dflt = (struct dst_metrics *)&dst_default_metrics; Why does this exist? To cast away the const? > struct dst_metrics *p = kzalloc_obj(*p, GFP_ATOMIC); > > if (!p) > return; > > + p->metrics[metric - 1] = val; > refcount_set(&p->refcnt, 1); > - f6i->fib6_metrics = p; > + if (cmpxchg(&f6i->fib6_metrics, dflt, p) != dflt) > + kfree(p); > + else > + return; > } > > - f6i->fib6_metrics->metrics[metric - 1] = val; > + struct dst_metrics *m = READ_ONCE(f6i->fib6_metrics); No variable declarations in the middle of a function please. > + WRITE_ONCE(m->metrics[metric - 1], val); > }