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Received: from shell.armlinux.org.uk ([2001:4d48:ad52:3201:5054:ff:fe00:4ec]:56048) by pandora.armlinux.org.uk with esmtpsa (TLSv1.2:ECDHE-RSA-AES256-GCM-SHA384:256) (Exim 4.90_1) (envelope-from ) id 1i3yEP-0003Py-U1; Sat, 31 Aug 2019 08:55:34 +0100 Received: from linux by shell.armlinux.org.uk with local (Exim 4.92) (envelope-from ) id 1i3yEG-0000pl-D3; Sat, 31 Aug 2019 08:55:24 +0100 Date: Sat, 31 Aug 2019 08:55:24 +0100 From: Russell King - ARM Linux admin To: Jing Xiangfeng Subject: Re: [PATCH] arm: fix page faults in do_alignment Message-ID: <20190831075524.GI13294@shell.armlinux.org.uk> References: <1567171877-101949-1-git-send-email-jingxiangfeng@huawei.com> <20190830133522.GZ13294@shell.armlinux.org.uk> <5D69D239.2080908@huawei.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <5D69D239.2080908@huawei.com> User-Agent: Mutt/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190831_005558_266283_1757A847 X-CRM114-Status: GOOD ( 15.36 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: kstewart@linuxfoundation.org, gustavo@embeddedor.com, gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, ebiederm@xmission.com, sakari.ailus@linux.intel.com, bhelgaas@google.com, tglx@linutronix.de, linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Sat, Aug 31, 2019 at 09:49:45AM +0800, Jing Xiangfeng wrote: > On 2019/8/30 21:35, Russell King - ARM Linux admin wrote: > > On Fri, Aug 30, 2019 at 09:31:17PM +0800, Jing Xiangfeng wrote: > >> The function do_alignment can handle misaligned address for user and > >> kernel space. If it is a userspace access, do_alignment may fail on > >> a low-memory situation, because page faults are disabled in > >> probe_kernel_address. > >> > >> Fix this by using __copy_from_user stead of probe_kernel_address. > >> > >> Fixes: b255188 ("ARM: fix scheduling while atomic warning in alignment handling code") > >> Signed-off-by: Jing Xiangfeng > > > > NAK. > > > > The "scheduling while atomic warning in alignment handling code" is > > caused by fixing up the page fault while trying to handle the > > mis-alignment fault generated from an instruction in atomic context. > > __might_sleep is called in the function __get_user which lead to that bug. > And that bug is triggered in a kernel space. Page fault can not be generated. > Right? Your email is now fixed? All of get_user(), __get_user(), copy_from_user() and __copy_from_user() _can_ cause a page fault, which might need to fetch the page from disk. All these four functions are equivalent as far as that goes - and indeed as are their versions that write as well. If the page needs to come from disk, all of these functions _will_ sleep. If they are called from an atomic context, and the page fault handler needs to fetch data from disk, they will attempt to sleep, which will issue a warning. -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTC broadband for 0.8mile line in suburbia: sync at 12.1Mbps down 622kbps up According to speedtest.net: 11.9Mbps down 500kbps up _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel