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 492FC1FAC4D; Thu, 5 Jun 2025 10:00:21 +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=1749117622; cv=none; b=G95elTSBPRkwFw+H3gCZbxqcRJIk7TCR1oW4TtbvUhzsi7Jgi2SLKrHsWK/is0uhs0zPY112W5CH9Ef3Pugandqps2SGsJI9S5Adr7EnONKzEZF4XitR6EQrdUoSZna5cIyYxpjoMG17hMidFsBOfYnQdrj2+xuP+rgbHuMp2Bs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1749117622; c=relaxed/simple; bh=5Eav7+G7caZZygl7Od69GSqH2G5p51M5I4/DH9iNkvA=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=KLttqdmCDpweNrGJzaWA16yDDmVQ14bVvMJYAOBoh2ReAQgzxqij5trWz1FfnJrEKK08GnFi+byYTF2B1RtiEl3IFdgpMWPpd1NPv/Y+1p1gZW5osSblQJRb4csM9fNTxAEmSpzCBwrMwwxTaFtlMhwrNmU8f6wTjcM+qB5xwMk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=CGEXQI/E; 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="CGEXQI/E" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9BCC6C4CEE7; Thu, 5 Jun 2025 10:00:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1749117621; bh=5Eav7+G7caZZygl7Od69GSqH2G5p51M5I4/DH9iNkvA=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=CGEXQI/E3ikPG3TMnj3L1o7OQn1gBi8hj6JUx52U/3rlrwN+n7jsg9Iax58rAQVLP ocQsfyyl0m0VJO+rk+8C4lTmfaa0wMiAs7ZAqrxtbDfhudaGxOKVbAEIH9QqA/ha+5 32ZOCTivQ9iI4ynr0DD6wdYByCfrovJyfu+6tgVWap84kn7sfGQvpIbRoF46CmI4QF TkDhNr/9Oh/+1LVvxWuIhucjz8Jsr5zZnd+ok+RfUgZox3qBanmRWV/MoTc3Pe/OOc O/EgOUs5EtI3HavqqB/5Io4BDPcNPZawPoXpJn6lP3IfJ2NHWbZ0OsoUD07k5Pmwy2 vV0uNT6dzLp0w== Received: from johan by xi.lan with local (Exim 4.97.1) (envelope-from ) id 1uN7OU-000000000Zb-1mJ1; Thu, 05 Jun 2025 12:00:19 +0200 Date: Thu, 5 Jun 2025 12:00:18 +0200 From: Johan Hovold To: Baochen Qiang Cc: Johan Hovold , Jeff Johnson , Miaoqing Pan , Remi Pommarel , linux-wireless@vger.kernel.org, ath12k@lists.infradead.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH v2 1/4] wifi: ath12k: fix dest ring-buffer corruption Message-ID: References: <20250604144509.28374-1-johan+linaro@kernel.org> <20250604144509.28374-2-johan+linaro@kernel.org> <6f3eb9fa-617e-4434-8fc4-33dd92c4bdd2@quicinc.com> Precedence: bulk X-Mailing-List: linux-kernel@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: <6f3eb9fa-617e-4434-8fc4-33dd92c4bdd2@quicinc.com> On Thu, Jun 05, 2025 at 04:41:32PM +0800, Baochen Qiang wrote: > On 6/4/2025 10:45 PM, Johan Hovold wrote: > > Add the missing memory barrier to make sure that destination ring > > descriptors are read after the head pointers to avoid using stale data > > on weakly ordered architectures like aarch64. > > > > The barrier is added to the ath12k_hal_srng_access_begin() helper for > > symmetry with follow-on fixes for source ring buffer corruption which > > will add barriers to ath12k_hal_srng_access_end(). > > > > Note that this may fix the empty descriptor issue recently worked around > > by commit 51ad34a47e9f ("wifi: ath12k: Add drop descriptor handling for > > monitor ring"). > > why? I would expect drunk cookies are valid in case of HAL_MON_DEST_INFO0_EMPTY_DESC, > rather than anything caused by reordering. Based on a quick look it seemed like this could possibly fall in the same category as some of the other workarounds I've spotted while looking into these ordering issues (e.g. f9fff67d2d7c ("wifi: ath11k: Fix SKB corruption in REO destination ring")). If you say this one is clearly unrelated, I'll drop the comment. > > @@ -343,9 +343,6 @@ static int ath12k_ce_completed_recv_next(struct ath12k_ce_pipe *pipe, > > goto err; > > } > > > > - /* Make sure descriptor is read after the head pointer. */ > > - dma_rmb(); > > - > > *nbytes = ath12k_hal_ce_dst_status_get_length(desc); > > > > *skb = pipe->dest_ring->skb[sw_index]; > > diff --git a/drivers/net/wireless/ath/ath12k/hal.c b/drivers/net/wireless/ath/ath12k/hal.c > > index 91d5126ca149..9eea13ed5565 100644 > > --- a/drivers/net/wireless/ath/ath12k/hal.c > > +++ b/drivers/net/wireless/ath/ath12k/hal.c > > @@ -2126,13 +2126,24 @@ void *ath12k_hal_srng_src_get_next_reaped(struct ath12k_base *ab, > > > > void ath12k_hal_srng_access_begin(struct ath12k_base *ab, struct hal_srng *srng) > > { > > + u32 hp; > > + > > lockdep_assert_held(&srng->lock); > > > > - if (srng->ring_dir == HAL_SRNG_DIR_SRC) > > + if (srng->ring_dir == HAL_SRNG_DIR_SRC) { > > srng->u.src_ring.cached_tp = > > *(volatile u32 *)srng->u.src_ring.tp_addr; > > - else > > - srng->u.dst_ring.cached_hp = READ_ONCE(*srng->u.dst_ring.hp_addr); > > + } else { > > + hp = READ_ONCE(*srng->u.dst_ring.hp_addr); > > + > > + if (hp != srng->u.dst_ring.cached_hp) { > > This consumes additional CPU cycles in hot path, which is a concern to me. > > Based on that, I prefer the v1 implementation. The conditional avoids a memory barrier in case the ring is empty, so for all callers but ath12k_ce_completed_recv_next() it's an improvement over v1 in that sense. I could make the barrier unconditional, which will only add one barrier to ath12k_ce_completed_recv_next() in case the ring is empty compared to v1. Perhaps that's a good compromise if you worry about the extra comparison? I very much want to avoid having both explicit barriers in the caller and barriers in the hal end() helper. I think it should be either or. > > + srng->u.dst_ring.cached_hp = hp; > > + /* Make sure descriptor is read after the head > > + * pointer. > > + */ > > + dma_rmb(); > > + } > > + } Johan