From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) (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 BB7163A1E63; Tue, 6 Jan 2026 00:39:19 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=216.40.44.16 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767659965; cv=none; b=QOj/abPAknJk2NAmTEd9bL/6S71DH23/m4PtDiXAZ7qjs2Zwl9pYtSOFsfhY/+wyKfxM45MZ8TGProd7LJXJ1K72WHJAGLro9bSFUhPjcyTCwH8ToBxRxRbhraB7NWaruicrtkAK94IdQ1BFFv3AQ+AhRUAe9dsWZEdy5sCh9ac= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767659965; c=relaxed/simple; bh=Oyrwnd6iX7XuIfagXrIfDAmgi63aTsjq/viTSjXf/1c=; h=Date:From:To:Cc:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=LTXX894nzCbNBnutyrbt/diOOL86XM9YU230rAIciZtB2IroYLE192Tuiz9tfqaLOsgWdH+3galfqh3FwzfZqhlrxXpIZb/TLpKMT2jGm4KrNRSPGn4SJIxisgoEs03zMBwix0IY0XcwMbkf3+Q9e2wdGhWBo/pPKXTHnArOWlQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=goodmis.org; spf=pass smtp.mailfrom=goodmis.org; arc=none smtp.client-ip=216.40.44.16 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=goodmis.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=goodmis.org Received: from omf19.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay10.hostedemail.com (Postfix) with ESMTP id D26E4C1757; Tue, 6 Jan 2026 00:39:12 +0000 (UTC) Received: from [HIDDEN] (Authenticated sender: rostedt@goodmis.org) by omf19.hostedemail.com (Postfix) with ESMTPA id 9309D20028; Tue, 6 Jan 2026 00:39:10 +0000 (UTC) Date: Mon, 5 Jan 2026 19:39:33 -0500 From: Steven Rostedt To: Laurent Pinchart Cc: Nicolas Dufresne , Stefan Klug , Xavier Roumegue , Mauro Carvalho Chehab , Sebastian Andrzej Siewior , Clark Williams , linux-media@vger.kernel.org, linux-kernel@vger.kernel.org, linux-rt-devel@lists.linux.dev Subject: Re: [PATCH 3/4] media: dw100: Fix kernel oops with PREEMPT_RT enabled Message-ID: <20260105193933.40485807@gandalf.local.home> In-Reply-To: <20260105235921.GI10026@pendragon.ideasonboard.com> References: <20260105-sklug-v6-16-topic-dw100-v3-1-dev-v1-0-65af34d04fd8@ideasonboard.com> <20260105-sklug-v6-16-topic-dw100-v3-1-dev-v1-3-65af34d04fd8@ideasonboard.com> <8a8ec84e5484d7a1a5e6fac9a5238f3cae66abc3.camel@ndufresne.ca> <20260105235921.GI10026@pendragon.ideasonboard.com> X-Mailer: Claws Mail 3.20.0git84 (GTK+ 2.24.33; x86_64-pc-linux-gnu) 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-Transfer-Encoding: 7bit X-Stat-Signature: 9g3fymwneetyszmde1d4grc7nedxsr7y X-Rspamd-Server: rspamout02 X-Rspamd-Queue-Id: 9309D20028 X-Session-Marker: 726F737465647440676F6F646D69732E6F7267 X-Session-ID: U2FsdGVkX1+jyBUrmzGz/LIwDu33A2ymGczKKjDEAkw= X-HE-Tag: 1767659950-586319 X-HE-Meta: U2FsdGVkX1+7VVNXxP1MAPsGOmGqsjr2CdajrWager3p8/66b/7VqrFtu8H8OFk5Qrbdbi7VIQE0ntXCY4/NJ/Jdp5AlFD+l73lG9mQkHbcwV4Vhxd3ITNHWRv/F9b23QBUgrx3rLtDMSAGSUrfpRg0ygrdm8rBRrArh0OzJFLAoENV84Hd72sO1ughXFVz9PyLzA75X1Oc8G4I59xp7uULpZXcHbXqCcemz9m4hBnXtYDiw2CTD5wPDbFUgsRFEamU8o2UhHTJS2B7j0ClDTiA6rwzXKpxveETZzmgR3i0hLL86ksNNxdO6ylI+qw4s/rmnyKL1X+FYtNvk+CU3NLRYEdTMOSflE/vvCrtOkstn6W6OwiZAU839Hz6lilyV On Tue, 6 Jan 2026 01:59:21 +0200 Laurent Pinchart wrote: > > That's interesting, do you plan to update more drivers ? There is a lot of m2m > > using hard IRQ to minimize the idle time (save a context switch), but RT support > > might be more worth then that. > > This is a part of PREEMPT_RT that puzzles me. By turning regular > spinlocks into mutexes, RT seems to break drivers that use those > spinlocks in hard IRQ handlers. That's a very large number of drivers > given how widespread regular spinlock usage is. Do drivers need to be > manually converted to either raw spinlocks or threaded IRQ handlers ? No. Pretty much all interrupts are converted into threaded interrupt handlers unless IRQF_NO_THREAD, IRQF_PERCPU, or IRQF_ONESHOT are specified. The interrupt line is disabled until the thread handler is called. > What about non-RT kernels, how can a driver avoid the thread scheduling > penalty in those cases, do they need to manually select between > request_irq() and request_threaded_irq() based on if RT is enabled ? > This puzzles me, it feels like I must be missing something. The issue here is that the interrupt handler specifies ONESHOT which causes the handler to be executed in hard interrupt context. -- Steve