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Wed, 02 Mar 2022 18:27:53 -0800 (PST) Received: from ubuntu.huawei.com ([119.3.119.19]) by smtp.googlemail.com with ESMTPSA id d15-20020a17090ab30f00b001b8e65326b3sm359822pjr.9.2022.03.02.18.27.34 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 02 Mar 2022 18:27:52 -0800 (PST) From: Xiaomeng Tong To: david.laight@aculab.com Cc: akpm@linux-foundation.org, alsa-devel@alsa-project.org, amd-gfx@lists.freedesktop.org, andriy.shevchenko@linux.intel.com, arnd@arndb.de, bcm-kernel-feedback-list@broadcom.com, bjohannesmeyer@gmail.com, c.giuffrida@vu.nl, christian.koenig@amd.com, christophe.jaillet@wanadoo.fr, dan.carpenter@oracle.com, dmaengine@vger.kernel.org, drbd-dev@lists.linbit.com, dri-devel@lists.freedesktop.org, gustavo@embeddedor.com, h.j.bos@vu.nl, intel-gfx@lists.freedesktop.org, intel-wired-lan@lists.osuosl.org, jakobkoschel@gmail.com, jgg@ziepe.ca, keescook@chromium.org, kgdb-bugreport@lists.sourceforge.net, kvm@vger.kernel.org, linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-aspeed@lists.ozlabs.org, linux-block@vger.kernel.org, linux-cifs@vger.kernel.org, linux-crypto@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, linux-fsdevel@vger.kernel.org, linux-iio@vger.kernel.org, linux-kernel@vger.kernel.org, linux-media@vger.kernel.org, linux-mediatek@lists.infradead.org, linux-pm@vger.kernel.org, linux-rdma@vger.kernel.org, linux-scsi@vger.kernel.org, linux-sgx@vger.kernel.org, linux-staging@lists.linux.dev, linux-tegra@vger.kernel.org, linux-usb@vger.kernel.org, linux-wireless@vger.kernel.org, linux1394-devel@lists.sourceforge.net, linux@rasmusvillemoes.dk, linuxppc-dev@lists.ozlabs.org, nathan@kernel.org, netdev@vger.kernel.org, nouveau@lists.freedesktop.org, rppt@kernel.org, samba-technical@lists.samba.org, tglx@linutronix.de, tipc-discussion@lists.sourceforge.net, torvalds@linux-foundation.org, v9fs-developer@lists.sourceforge.net, xiam0nd.tong@gmail.com Subject: RE: [PATCH 2/6] treewide: remove using list iterator after loop body as a ptr Date: Thu, 3 Mar 2022 10:27:29 +0800 Message-Id: <20220303022729.9321-1-xiam0nd.tong@gmail.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <1077f17e50d34dc2bbfdf4e52a1cb2fd@AcuMS.aculab.com> References: <1077f17e50d34dc2bbfdf4e52a1cb2fd@AcuMS.aculab.com> Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Wed, 2 Mar 2022 14:04:06 +0000, David Laight wrote: > I think that it would be better to make any alternate loop macro > just set the variable to NULL on the loop exit. > That is easier to code for and the compiler might be persuaded to > not redo the test. No, that would lead to a NULL dereference. The problem is the mis-use of iterator outside the loop on exit, and the iterator will be the HEAD's container_of pointer which pointers to a type-confused struct. Sidenote: The *mis-use* here refers to mistakely access to other members of the struct, instead of the list_head member which acutally is the valid HEAD. IOW, you would dereference a (NULL + offset_of_member) address here. Please remind me if i missed something, thanks. > OTOH there may be alternative definitions that can be used to get > the compiler (or other compiler-like tools) to detect broken code. > Even if the definition can't possibly generate a working kerrnel. The "list_for_each_entry_inside(pos, type, head, member)" way makes the iterator invisiable outside the loop, and would be catched by compiler if use-after-loop things happened. Can you share your "alternative definitions" details? thanks! -- Xiaomeng Tong