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Tue, 9 Dec 2025 09:28:25 +0800 (CST) Received: from kwepemj100009.china.huawei.com (unknown [7.202.194.3]) by mail.maildlp.com (Postfix) with ESMTPS id D0A49180BD8; Tue, 9 Dec 2025 09:30:25 +0800 (CST) Received: from DESKTOP-A37P9LK.china.huawei.com (10.67.109.17) by kwepemj100009.china.huawei.com (7.202.194.3) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1544.11; Tue, 9 Dec 2025 09:30:24 +0800 From: Xie Yuanbin To: CC: , , , , , , , , , , , , , , , , Subject: Re: [Bug report] hash_name() may cross page boundary and trigger sleep in RCU context Date: Tue, 9 Dec 2025 09:30:21 +0800 Message-ID: <20251209013021.2537-1-xieyuanbin1@huawei.com> X-Mailer: git-send-email 2.51.0 In-Reply-To: References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain X-Originating-IP: [10.67.109.17] X-ClientProxiedBy: kwepems200001.china.huawei.com (7.221.188.67) To kwepemj100009.china.huawei.com (7.202.194.3) X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 3C335120006 X-Stat-Signature: m6oot37huaxno1yzckb88ecw74zgssek X-Rspam-User: X-HE-Tag: 1765243830-889732 X-HE-Meta: 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 cwKfBh25 yYYYiZ+tVISAYZcYzGdDGz3kzGPCxPeYLiZ+7d1PTbyjFFCA= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, 8 Dec 2025 15:43:56 +0000, Russell King wrote: > On Mon, Dec 08, 2025 at 09:18:42PM +0800, Xie Yuanbin wrote: >> I had indeed been lacking in consideration regarding do_alignment() >> before, so thank you for reply. But, may I ask that, is there a scenario >> where user-mode access to kernel addresses causes an alignment fault >> (do_alignment())? > > If you mean, won't permission errors be detected first, then no. > Alignment is one of the first things that is checked if alignment > faults are enabled. > > So yes, if userspace attempts an unaigned load of a kernel address, > and the CPU does not support / have enabled unaigned load support, > then we will get a data abort with the FSR indicating an alignment > fault. So do_alignment() wil be entered. > > Whether branch predictor handling needs to happen in this path is > a separate question, but as it's highly likely we'll take an > exception anyway and userspace is doing Bad Stuff, I feel it's > better to be over-cautious. Thanks for your reply. I know it now, and thank you.