From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from pandora.armlinux.org.uk (pandora.armlinux.org.uk [78.32.30.218]) (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 EEAEE2144C7; Mon, 8 Dec 2025 10:07:37 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=78.32.30.218 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1765188460; cv=none; b=sx746ZWRuG1XSunwjKcgSof4m5tmrmGiZq4d9OT7UUaRHMKwzYh1Q4kdcTBkXr3YBbqfeYj1ZiKtvitU9RCYDrvPjm7Ys7j72oVV+3Spy9+ce2UeVIeqMhMoq0D2lWI6B7z14Fetes0cLIQGd95InwUYnIbRGwPqbg7+VbKU08I= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1765188460; c=relaxed/simple; bh=zzoPaZTOchC0rfeZyXPZrjhQIa0OL/Xj8WihiQjr7T0=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=hePMSTADUreT9v3nhNEksOUzw3kbVtBPT4tZbyCqAJlJMG2NmD7Q206Lplo9LFwfYw1hpN9/Pa5ju2kP4W20ER2GTU0MdxhYuSO9cdvgAf73GZ3QNOKypQdgwXsIylntPGVFGtbaPt4FokmlCKa8kkRapBJS2xpz2SVv/KQEdFU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=armlinux.org.uk; spf=none smtp.mailfrom=armlinux.org.uk; dkim=pass (2048-bit key) header.d=armlinux.org.uk header.i=@armlinux.org.uk header.b=Yq1FcK78; arc=none smtp.client-ip=78.32.30.218 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=armlinux.org.uk Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=armlinux.org.uk Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=armlinux.org.uk header.i=@armlinux.org.uk header.b="Yq1FcK78" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=armlinux.org.uk; s=pandora-2019; h=Sender:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=T2q3qIpB2rZdmxgNfQrdMX7fXgjlUn1FNnbk0gfok3I=; b=Yq1FcK78y3w6nkgHfG8T/MDxrk IxPuchTO5iIOBoYJahU8xB/t/TBjpRAjm/4AFYdSRl6UIeQ11DcKzstMyYC6itiWWr6tdIPLP5Y7H oqkVhHPMfM+F4oWLKsC9B0VaLXpMAwRhWiAV1s4LEV2C3JSjEkHE7Kgc003Hh1bBk4X6AkWRoEpVW oT+77Xz6SycoycRX1c0LeynFqnbm7G1n5TtAHY42t4W9I1dP7Iese3Pe5JIL2yvuHdlvtUE0NKd53 Oe9oqVQJa7G5XePlJlodhUKIs/7elRd9CSi08xcHHqeO66+yWWWAe3BmmTNtZmFjbpOl1VDVCQCzB svgD+L+w==; Received: from shell.armlinux.org.uk ([fd8f:7570:feb6:1:5054:ff:fe00:4ec]:48358) by pandora.armlinux.org.uk with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.98.2) (envelope-from ) id 1vSY9S-000000007bR-0fW9; Mon, 08 Dec 2025 10:07:30 +0000 Received: from linux by shell.armlinux.org.uk with local (Exim 4.98.2) (envelope-from ) id 1vSY9N-000000004vY-2kGQ; Mon, 08 Dec 2025 10:07:25 +0000 Date: Mon, 8 Dec 2025 10:07:25 +0000 From: "Russell King (Oracle)" To: Xie Yuanbin Cc: viro@zeniv.linux.org.uk, akpm@linux-foundation.org, brauner@kernel.org, catalin.marinas@arm.com, hch@lst.de, jack@suse.com, linux-arm-kernel@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, pangliyuan1@huawei.com, torvalds@linux-foundation.org, wangkefeng.wang@huawei.com, will@kernel.org, wozizhi@huaweicloud.com, yangerkun@huawei.com Subject: Re: [Bug report] hash_name() may cross page boundary and trigger sleep in RCU context Message-ID: References: <20251208023206.44238-1-xieyuanbin1@huawei.com> Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20251208023206.44238-1-xieyuanbin1@huawei.com> Sender: Russell King (Oracle) On Mon, Dec 08, 2025 at 10:32:06AM +0800, Xie Yuanbin wrote: > On Fri, 5 Dec 2025 12:08:14 +0000, Russell King wrote: > > Right, let's split these issues into separate patches. Please test this > > patch, which should address only the hash_name() fault issue, and > > provides the basis for fixing the branch predictor issue. > > I conducted a simple test, and it seems that both the hash_name() > might sleep issue and the branch predictor issue have been fixed. This isn't entirely fixed. A data abort for an alignment fault (thus calling do_alignment()) will enable interrupts, and then may call do_bad_area(). We can't short-circuit this path like we can with do_page_fault() as alignment faults from userspace can be valid for the vectors page - not that we should see them, but that doesn't mean that there isn't something in userspace that does. > BTW, even with this patch, test cases may still fail. There is another > bug in hash_name() will also be triggered by the testcase, which will be > fixed in this patch: > Link: https://lore.kernel.org/20251127025848.363992-1-pangliyuan1@huawei.com That patch got missed - I'm notoriously bad at catching every email. There's just way too much email coming in. > Test case is from: > Link: https://lore.kernel.org/20251127140109.191657-1-xieyuanbin1@huawei.com > > Test in commit 6987d58a9cbc5bd57c98 ("Add linux-next specific files for > 20251205") from linux-next branch. > > I still have a question about this patch: Is > ```patch > + if (interrupts_enabled(regs)) > + local_irq_enable(); > ``` > necessary? Although this implementation is closer to the original code, > which can reduce side effects, do_bad_area(), do_sect_fault(), > and do_translation_fault() all call __do_kernel_fault() with interrupts > disabled. It's to keep the behaviour closer to the original as possible, on the principle of avoiding unnecessary behavioural changes to the code. As noted above, do_bad_area() can be called with interrupts enabled. Whether RT folk would be happy removing that is a different question, given that they want as much of the kernel to be preemptable. -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last!