From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) (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 C478D35958; Thu, 2 Apr 2026 07:03:21 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=193.142.43.55 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775113402; cv=none; b=jAonNiW7L5hO1A8dlWg52LD2ALNPOFXreJiPVeBad0Hc8HwXwuZV/m6abaCCReJFaZ+wszesas1soosTzLsu5sha+rm040QfBHVRsa9H7qwiM53Fa7LeyhciwElbLJerROu7dVwxLlQ9BbdvV7jpM/onb4UnFUgGlK4ROLiXT+8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775113402; c=relaxed/simple; bh=NPgKlAJa6fM9rj55i5LCX5n3X5ZK1g15EE2zn8d4w/E=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=uzCQEYso0KpiX9ElSmRd8mmFMr/T/hOjK91SvrdLdNR388+yddPo51QFxdlWnkM8vf5lk44SKicJuq5yGYHoCP7A2X6Em8jNWSOZ6dIok3M/cwFSkfXGukFPjkGChNduss9Cc49RpsXgqgZdEdK7se2oXw6m4DgdfA6Fp1BaxaM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de; spf=pass smtp.mailfrom=linutronix.de; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=v+pKyJr5; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=Ginns0Qj; arc=none smtp.client-ip=193.142.43.55 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linutronix.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="v+pKyJr5"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="Ginns0Qj" Date: Thu, 2 Apr 2026 09:03:19 +0200 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1775113400; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=t40wZeCuWVnwzUJhQxO88spnP0YMQ53Htf2Z4u5PKL8=; b=v+pKyJr5yqSNL/P0e98/BkB5CZSVO+ZdB9ZajyuzMJNXkL2A25z0UFxl0FlciQxpMcBx8v YtCausnlRb6+se84j1eIVuavsBPQW9ADU2tHLewanLfeehKQV3l/TIE3wBtxrKFVJKAEcU wGhdd6vbV54Cvu9kdXqTt5nRU2oy9rPOI23z1zxtdacRZM08CsBxfUvnyXpbBFKpPDuOmj 2azymZksz6RJowTwLkbr2ao9HrwWs1x5jioiUxw+K/7YcxP0sdD3GY/cIfuwCgwAkEY3j9 eGGkFh+pb9GdyXB4+8QsLZvCxkfRSzYuNZm9ra0RUi89uMWBFL68YrguK6huCA== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1775113400; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=t40wZeCuWVnwzUJhQxO88spnP0YMQ53Htf2Z4u5PKL8=; b=Ginns0QjrOTleComWPH5A4fRRNpHr/vaP7CZKKw6MPZVyAeUlSfmZmS+2EeEdd28nyDKma OXxm5kxPQkqFL9Dg== From: Sebastian Andrzej Siewior To: Daniel Vacek Cc: edumazet@google.com, kuba@kernel.org, linux-kernel@vger.kernel.org, linux-rt-devel@lists.linux.dev, netdev@vger.kernel.org, spasswolf@web.de, tglx@linutronix.de Subject: Re: "Dead loop on virtual device" error without softirq-BKL on PREEMPT_RT Message-ID: <20260402070319.vhRd6c-f@linutronix.de> References: <2369ba83d204290dcfe157aed3f943206213b979.camel@web.de> <20260218073036.AlkNRoAP@linutronix.de> <20260226172927.2Ck9wZMw@linutronix.de> <20260318103009.2120920-1-neelx@suse.com> <20260318111849._MMol8Hr@linutronix.de> <20260318145101._iaDDpbE@linutronix.de> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: On 2026-04-01 18:55:43 [+0200], Daniel Vacek wrote: > > > > The above was me thinking and does not even compile for !RT. Commit > > > > b824c3e16c190 ("net: Provide a PREEMPT_RT specific check for > > > > netdev_queue::_xmit_lock") is what was merged in the end. > > Thinking about it again, wouldn't it be better to have one generic > solution rather then special-casing for PREEMPT_RT vs. !PREEMPT_RT? PREEMPT_RT and !PREEMPT_RT is fundamentally different here. The one is not preemptible and records the CPU of the lock owner to detect a recursive deadlock. The other is preemptible, uses a different locking type/ class which records the lock owner which can be utilised for this purpose. A generic thing would be to remove this and rely on lockdep. This could work if it is only a devel thing and never "I setup something and make a loop" sort of thing. > --nX Sebastian