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 F2E8E1CA81; Fri, 8 Aug 2025 19:05:35 +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=1754679936; cv=none; b=KggoOh+xJ5aUyPTn3Fttyw3mrey3xOygTBBZW/F/0lLiwCsIfOT/4bEcu7GQuqf2n+AOlAlsbogoSphJPT6501L3w2O6TosQzsJU3PMEkiXo7bEQcVrMfusEE3lb0Vzx/jQXStqCPCfScWi3pYdEDMsU8kkiXnG1JXb/zWZauug= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1754679936; c=relaxed/simple; bh=9sNZifZ906dYt7wIbV9eoAh1hSVh4+0uqV8iP9M7bIw=; h=Date:From:To:Cc:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=fQYyDgppFoy09sOFjMr2d4B3tBvVbA/WZlJqCNF9wd/GZ1Sywd1lGPqDP8767tx5+AjBb9PqZX+X93Tb3ynIZIyXhX2+Y/Mf0OFHCWx9mRMD9L/RXeMsCbqsXEZvc962NIPNZscqTjM/9NTGFV0wUm6O37MSaftBYHlUhqHJW14= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Db1XJ4G8; 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="Db1XJ4G8" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 06FB2C4CEED; Fri, 8 Aug 2025 19:05:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1754679935; bh=9sNZifZ906dYt7wIbV9eoAh1hSVh4+0uqV8iP9M7bIw=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=Db1XJ4G8RHVrCzWfz7X+y6PLjFRKCtezVLfArElwa49X52xu0y0wb6fzwZrtOrW9e RMnQRFOZaNXpa21Kqqr5QiK4V3xMkEeHujpZ07QczjdcmfQU618W5zEiJ17LieCfq1 iINq8vBHGZMWU4qnv02JN2genYJBfNm7A22qVqem5xL6rBjYYBc/k6CGwXAHVhZRI7 eTFmJed6OFXe5tLcP6rcwsVBiDwaPyAStPzggj3y53kBOAfa5HhPuYMfAq2JfLosJd +7N3L8sQPGWbHdoD5Q5WG/1QkS4zolLfOlbYqHSIq5JYPrcVb2kCX7i0RFyk7cxraX LDyxQrjRODaKQ== Date: Fri, 8 Aug 2025 12:05:34 -0700 From: Jakub Kicinski To: Suraj Gupta Cc: , , , , , , , , , , , Subject: Re: [PATCH net] net: xilinx: axienet: Increment Rx skb ring head pointer after BD is successfully allocated in dmaengine flow Message-ID: <20250808120534.0414ffd0@kernel.org> In-Reply-To: <20250805191958.412220-1-suraj.gupta2@amd.com> References: <20250805191958.412220-1-suraj.gupta2@amd.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 Wed, 6 Aug 2025 00:49:58 +0530 Suraj Gupta wrote: > In DMAengine flow, AXI DMA driver invokes callback before freeing BD in > irq handling path. > In Rx callback (axienet_dma_rx_cb()), axienet driver tries to allocate > new BD after processing skb. > This will be problematic if both AXI-DMA and AXI ethernet have same > BD count as all Rx BDs will be allocated initially and it won't be > able to allocate new one after Rx irq. Incrementing head pointer w/o > checking for BD allocation will result in garbage values in skb BD and > cause the below kernel crash: > > Unable to handle kernel paging request at virtual address fffffffffffffffa > > Internal error: Oops: 0000000096000006 [#1] SMP > pc : axienet_dma_rx_cb+0x78/0x150 > lr : axienet_dma_rx_cb+0x78/0x150 > Call trace: > axienet_dma_rx_cb+0x78/0x150 (P) > xilinx_dma_do_tasklet+0xdc/0x290 > tasklet_action_common+0x12c/0x178 > tasklet_action+0x30/0x3c > handle_softirqs+0xf8/0x230 > Do you mean that we're incrementing lp->rx_ring_head before we know that the submission will succeed? Potentially leaving an uninitialized entry (say at index n), next attempt will try to use the next entry (n + 1) but the completion will not know about the skip so it will try to complete entry n ? This is really not coming thru in your explanation. The fix itself seems incomplete. Even if we correctly skip the increment we will never try to catch up with the allocations, the ring will have fewer outstanding Rx skbs until reset, right? Worst case we drop all the skbs and the ring will be empty, no Rx will happen until reset. The shutdown path seems to be checking for skb = NULL so I guess it's correct but good to double check.. -- pw-bot: cr