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 8265718C933 for ; Thu, 31 Jul 2025 08:02:51 +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=1753948971; cv=none; b=jee+HCucL/llcrPoZy2scMVL+MbyHK1Da+aIknd1zx3IRb+VdeKvk3exbLQz/atJAKtKuJuN9TN6teQIZ0wvhFhB76hFXhtmviNMVf3NJgqO0DtIQeo6J2Z0FoAXz0ZcJA2J6EG1bfJuXvXmIuMaOmF5oeadbNmUMATzt8yStdo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753948971; c=relaxed/simple; bh=9Z5DzLNxeW75H0JmSCyuAbv60UL/uTn/jONG/a++W1k=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=gJn0rFoffo6y6OoxIFpMUT7VaLNM6y9XYsQJfIu8Ddk6zxuJ3Pt4SWadbueIYq5kFMVz5BcsYLcwW9N2cdhU9GAA8TdiJjJ0CtXrRSJNTf0VOEY6Z/8383hjJHgc8zsVq7XUeI5quRLob9VWsLKUr9JEWnCkqb4zgDPDQ+Tk4nI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=hoPL2DeG; 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="hoPL2DeG" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 31EF6C4CEF5; Thu, 31 Jul 2025 08:02:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1753948971; bh=9Z5DzLNxeW75H0JmSCyuAbv60UL/uTn/jONG/a++W1k=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=hoPL2DeGjvXB+Ut7mDHzNstCWe0F+g81eEx5aA+V59cEG9LHB1hOzkHNabJXujUfR XIgupSB2GYxqTcGSNqpIs/n2sg5hZVyL6x1pl3U24jti22CEaBXaGqBldxLh2ft+7G tfV+3Be2nOIYSptD0ytXi//OKj2Nfbkqm2hClWL9MvYSBbAFuZQkU8o3g0DlZ3IUOK uFJa6I8Al29+7Eq9M1GvpGW/TgOWl4tVcvxiWwvA5iBHi6ThQjMKGAC/wiiQCCZ4RK 19spkVW9sU51X4gYVxFCnyBj9p43d0k1kEBnGoideJGC0kSyLHtBq0VbP6scoGGl9N Xz4JMTQKL+0/w== Message-ID: <38a023cd-4e67-418f-bc27-e272c5484671@kernel.org> Date: Thu, 31 Jul 2025 10:02:48 +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] irq: simplify irq_im_handle_irq() To: Thomas Gleixner , Yury Norov Cc: linux-kernel@vger.kernel.org, Bartosz Golaszewski References: <20250719211818.402115-1-yury.norov@gmail.com> <87zfcxtz6t.ffs@tglx> <87o6tdtupb.ffs@tglx> 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 Hi, On 21. 07. 25, 17:44, Thomas Gleixner wrote: > On Mon, Jul 21 2025 at 10:27, Yury Norov wrote: >> On Mon, Jul 21, 2025 at 04:07:22PM +0200, Thomas Gleixner wrote: >> find_next_bit() and for_each_bit() cannot be used in concurrent >> environment, and having atomic clear_bit() is meaningless here. >> Two concurrent processes, if running in parallel, may pick the >> same offset, ending up executing the handle_simple_irq() twice. > > The irq work cannot be run in parallel on multiple CPUs. It's guaranteed > that only one irq work handler runs at a time. So irq_sim_handle_irq() > is fully serialized by the irq work magic. > > But the bitmap can be modified concurrently, which is not a problem. Actually, it is (IMO): while (!bitmap_empty(work_ctx->pending, work_ctx->irq_count)) { offset = find_next_bit(work_ctx->pending, work_ctx->irq_count, offset); clear_bit(offset, work_ctx->pending); irqnum = irq_find_mapping(work_ctx->domain, offset); handle_simple_irq(irq_to_desc(irqnum)); } If another CPU sets a bit X in the beginning of the work_ctx->pending bitmap while this is running for some time already (that means offset is already greater that that X), bitmap_empty() will be always true and this spins forever (or crashes). It is because find_next_bit() will never return that bit X -- so clear_bit() will never happen on that. What is worse, find_next_bit() will return work_ctx->irq_count and both clear_bit() and irq_find_mapping() will touch an OOB memory. Or what am I missing? find_next_bit_wrap() would cure that. thanks, -- js suse labs