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 CC81431352C; Mon, 15 Dec 2025 17:10:49 +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=1765818650; cv=none; b=TGQASUT5C3OaV6K2E8FJSWrov1NFc4MTEyTt+MHacmjYcvq8XtSIScvublHRNvM1FxEauobtRI0z8QUBTAR+nrJWCX+SzEs1Q+yZ/qjlYCfV0HDgaqorGhfKyc+2kS1Jry6TqcK3KLfpf8HTHyhEPkx4q5iA41QkIZ0AFHk3CE0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1765818650; c=relaxed/simple; bh=cwMR/Fk5tha92MiDNpmUeFP+QNMa9XhwhgULZKix1PY=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=mczn1qRV9iFy1wQ8mFkp6Xehrgg9QkGDjwDM9PsyfKrCCl1veT0C2o7G8wE3Mqkh7L/qCVcnkyHNriGfohRN6udTGpXpratD3xdmnLnNVkLhB1PQUZJ6Bd2AaMI1CZmXBA7mHZf62sdvxW/cEnYbBthbpM7l7l/U4Nii8c6KS2w= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=FZMVOEwP; 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="FZMVOEwP" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0F880C4CEF5; Mon, 15 Dec 2025 17:10:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1765818648; bh=cwMR/Fk5tha92MiDNpmUeFP+QNMa9XhwhgULZKix1PY=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=FZMVOEwPzqZZWOFPQ6Wa00Okn6d0OJMvDCcP+Ke/6f59VpIzMzvl9yX9EQWOGXLL3 k9G8gIrcVqMjIjyJBnyNy7wyFBMTpxQ0PgBtCdwsOj2DqJL8Px3KVTBbjZs3TXeW06 Qx3dtmbRvVyym2X9vldBHcSErJ+2/7lD6UYGgbGCAOnvcuDB874wIsHJluhHL9uTd5 sOqtEe4FkdAKX5H89+7i5gVZ2DT6GO/hRx+dS83zP5R+d9Do1kJmKi37Qxa0YRiMI7 fHE3p1zn0APIXoXguSrqvXgkJamO9sentpByvn77geIUgGt2kX7MMn7Wj7+SBHZj+8 XnzY4Tz4lrE2g== Date: Mon, 15 Dec 2025 17:10:43 +0000 From: Simon Horman To: Yeoreum Yun Cc: nico@fluxnic.net, andrew+netdev@lunn.ch, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, bigeasy@linutronix.de, clrkwllms@kernel.org, rostedt@goodmis.org, dongdong.deng@windriver.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linux-rt-devel@lists.linux.dev, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH v2] smc91x: fix broken irq-context in PREEMPT_RT Message-ID: References: <20251212190338.2318843-1-yeoreum.yun@arm.com> Precedence: bulk X-Mailing-List: linux-rt-devel@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20251212190338.2318843-1-yeoreum.yun@arm.com> On Fri, Dec 12, 2025 at 07:03:38PM +0000, Yeoreum Yun wrote: > When smc91x.c is built with PREEMPT_RT, the following splat occurs > in FVP_RevC: > > [ 13.055000] smc91x LNRO0003:00 eth0: link up, 10Mbps, half-duplex, lpa 0x0000 > [ 13.062137] BUG: workqueue leaked atomic, lock or RCU: kworker/2:1[106] > [ 13.062137] preempt=0x00000000 lock=0->0 RCU=0->1 workfn=mld_ifc_work > [ 13.062266] C > ** replaying previous printk message ** > [ 13.062266] CPU: 2 UID: 0 PID: 106 Comm: kworker/2:1 Not tainted 6.18.0-dirty #179 PREEMPT_{RT,(full)} > [ 13.062353] Hardware name: , BIOS > [ 13.062382] Workqueue: mld mld_ifc_work > [ 13.062469] Call trace: > [ 13.062494] show_stack+0x24/0x40 (C) > [ 13.062602] __dump_stack+0x28/0x48 > [ 13.062710] dump_stack_lvl+0x7c/0xb0 > [ 13.062818] dump_stack+0x18/0x34 > [ 13.062926] process_scheduled_works+0x294/0x450 > [ 13.063043] worker_thread+0x260/0x3d8 > [ 13.063124] kthread+0x1c4/0x228 > [ 13.063235] ret_from_fork+0x10/0x20 > > This happens because smc_special_trylock() disables IRQs even on PREEMPT_RT, > but smc_special_unlock() does not restore IRQs on PREEMPT_RT. > The reason is that smc_special_unlock() calls spin_unlock_irqrestore(), > and rcu_read_unlock_bh() in __dev_queue_xmit() cannot invoke > rcu_read_unlock() through __local_bh_enable_ip() when current->softirq_disable_cnt becomes zero. > > To address this issue, replace smc_special_trylock() with spin_trylock_irqsave(). > > Fixes: 8ff499e43c53 ("smc91x: let smc91x work well under netpoll") > Signed-off-by: Yeoreum Yun > --- > This patch based on v6.18. > > History > ======== > > >From v1 to v2: > - remove debug log. > - https://lore.kernel.org/all/20251212185818.2209573-1-yeoreum.yun@arm.com/ > Firstly, I'd like to note that it seems to me that the last non-trivial update to this driver seems to have occurred back in 2016. Do you know if it is still actively used? I agree that this patch seems appropriate as a bug fix. But I do wonder if, as a follow-up for net-next when it re-opens, smc_special_*lock could be removed entirely. Other than being the source of this bug (which I guess is special), they don't seem very special anymore. Perhaps they were once, but that time seems to have passed. Regarding the Fixes tag. I wonder if this one, which post-dates the currently cited commit is correct. It seems to be when RT variants of these locks was introduced. Fixes: 342a93247e08 ("locking/spinlock: Provide RT variant header: ") Lastly, for reference, when posting fixes for Networking code, please: * Target the patches at net like this: [PATCH net] ... * Allow at least 24h to pass before posting updated patch versions More can be found here: https://docs.kernel.org/process/maintainer-netdev.html Reviewed-by: Simon Horman