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From: Kent Overstreet To: Youling Tang Cc: Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Youling Tang Subject: Re: [PATCH] mm: list_lru: Fix NULL pointer dereference in list_lru_add() Message-ID: References: <20240712032554.444823-1-youling.tang@linux.dev> <8ce42a2e-783f-4244-8e75-21dcd578adf5@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <8ce42a2e-783f-4244-8e75-21dcd578adf5@linux.dev> X-Migadu-Flow: FLOW_OUT X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: F181110001F X-Stat-Signature: j48fphybk4qk7tiden8dpubtahnwnczn X-Rspam-User: X-HE-Tag: 1720799352-571001 X-HE-Meta: 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 VZUla/NF ZdpXvDWDfJQ8FiW1xQr+JPCX0Ke8QVCcVnYuuXVYRt/2QLuJPyyRzacqy1JR8+kzcLMxBj09u/E/i+xPp/PsJvfpzNJcOtCkax4mdSobwcIfx+mXmq26Us8+4RykJ4XRpXY9A/cl0GrJ8QxDDTuKGiuHs80A4V4UzLa9ENbazfyABgKPQ0tl0Eu8TiqrTsqZq/OtAdsIhpKwT35p5W7k0Sjr2TtnzwMqKYD4k 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 Fri, Jul 12, 2024 at 12:28:57PM GMT, Youling Tang wrote: > Hi, Kent > > On 12/07/2024 12:07, Kent Overstreet wrote: > > On Fri, Jul 12, 2024 at 11:25:54AM GMT, Youling Tang wrote: > > > From: Youling Tang > > > > > > Note that list_lru_from_memcg_idx() may return NULL, so it is necessary > > > to error handle the return value to avoid triggering NULL pointer > > > dereference BUG. > > > > > > The issue was triggered for discussion [1], > > > Link [1]: https://lore.kernel.org/linux-bcachefs/84de6cb1-57bd-42f7-8029-4203820ef0b4@linux.dev/T/#m901bb26cdb1d9d4bacebf0d034f0a5a712cc93a6 > > I see no explanation for why this is the correct fix, and I doubt it is. > > What's the real reason for the NULL lru_list_one, and why doesn't this > > come up on other filesystems? > We can break it down into two questions (independent of each other): > 1) Error handling is necessary when l (lru_list_one) is NULL here. No, you're just hiding the actual bug - since I wasn't clear, I'm naking this patch.