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 B6E8F2D29C7 for ; Tue, 22 Jul 2025 07:37:56 +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=1753169876; cv=none; b=jZ5kWMPHxRblr/5EXbsTp9ycByQ92ZyrVjJMgG+SVUkV4VaUR7Xei0Pa6Ns9HNZdaE/IGloi3B2vPtnYjGHyDu671AYuouKnEGlDVwQV2jIsdEe988uuoh/Ajmh7RyRQvIgcXB/ujdLwri6nb07XfB3wuNLUA1Fyj+8IP2UZons= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753169876; c=relaxed/simple; bh=KEQ+1POGwaZLlQgPaSk5QV7eY0bwG1NFxzwzgBt6IOY=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=BhV3KqYtq6oqtVtSMhDMh9ClBtLmVDs0s3ytjSPBB6E4axUH+raYx2H3TaEp/XFswXvvZiw+lU+gZwtgtM2gOyOUjR6AhpTFLRkdoGnWQ/xO76ZBlnKtHzL0IMLIlLmKqADWZo8/jSsL3OS9OgXprEjoiUg3tw4YZAPBfxr0GnA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=JNe1h8Q8; 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="JNe1h8Q8" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2A87DC4CEEB; Tue, 22 Jul 2025 07:37:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1753169876; bh=KEQ+1POGwaZLlQgPaSk5QV7eY0bwG1NFxzwzgBt6IOY=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=JNe1h8Q8yecuwmh3vm/HYNH/I/9bA9rU2cr1dJikFEVczhC6GfSvpzJlQe+ekCNdv oSu8zS2k+UThTq2OSG8fbCr7uz3sV2OxFYbX0iLkEzmRx3mltfY0gThzk37Yx9UCsa KnSB1rUacxc4Sl9r6dSKmzr91FuStL7qBhx+vwBLYa6AwXgJXY/8+DgotXc46R0B3L tJ2BP8hKCBebR1h8VtU1PdIKnWu/BXhJYr9M4cscchvMzKDILsRQ8kUuaPuEzKXTp/ 7s+5sn2d5zF1OfkLGOZgtYdvUPNEY8+GOUw53yX5vcW8FQNZ9ydrx5M3pTNqCBC83l kUowG0DmFMq6w== Message-ID: <7d18317b-5a3a-435e-8620-6f978dc84e8f@kernel.org> Date: Tue, 22 Jul 2025 09:37:53 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [patch 4/4] genirq: Prevent migration live lock in handle_edge_irq() To: Thomas Gleixner , LKML Cc: Liangyan , Yicong Shen References: <20250718184935.232983339@linutronix.de> <20250718185312.076515034@linutronix.de> Content-Language: en-US From: Jiri Slaby Autocrypt: addr=jirislaby@kernel.org; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 18. 07. 25, 20:54, Thomas Gleixner wrote: > Yicon reported and Liangyan debugged a live lock in handle_edge_irq() > related to interrupt migration. > > If the interrupt affinity is moved to a new target CPU and the interrupt is > currently handled on the previous target CPU for edge type interrupts the > handler might get stuck on the previous target: > > CPU 0 (previous target) CPU 1 (new target) > > handle_edge_irq() > repeat: > handle_event() handle_edge_irq() > if (INPROGESS) { > set(PENDING); > mask(); > return; > } > if (PENDING) { > clear(PENDING); > unmask(); > goto repeat; > } > > The migration in software never completes and CPU0 continues to handle the > pending events forever. This happens when the device raises interrupts with > a high rate and always before handle_event() completes and before the CPU0 > handler can clear INPROGRESS so that CPU1 sets the PENDING flag over and > over. This has been observed in virtual machines. > > Prevent this by checking whether the CPU which observes the INPROGRESS flag > is the new affinity target. If that's the case, do not set the PENDING flag > and wait for the INPROGRESS flag to be cleared instead, so that the new > interrupt is handled on the new target CPU and the previous CPU is released > from the action. > > This is restricted to the edge type handler and only utilized on systems, > which use single CPU targets for interrupt affinity. LGTM Reviewed-by: Jiri Slaby > Reported-by: Yicong Shen > Reported-by: Liangyan > Signed-off-by: Thomas Gleixner > Link: https://lore.kernel.org/all/20250701163558.2588435-1-liangyan.peng@bytedance.com thanks, -- js suse labs