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Wed, 26 Aug 2026 07:10:33 -0700 (PDT) Received: from jgg by wakko with local (Exim 4.97) (envelope-from ) id 1wzEKm-0000000FQfM-2V2G; Wed, 26 Aug 2026 11:10:32 -0300 Date: Wed, 26 Aug 2026 11:10:32 -0300 From: Jason Gunthorpe To: Liu Dalin Cc: Andrew Morton , David Hildenbrand , John Hubbard , Peter Xu , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Liu Dalin , Deng yingchao , Qin yungao , Luo Qiu Subject: Re: [PATCH] mm/gup: add NULL check for unlocked parameter in fixup_user_fault() Message-ID: <20260826141032.GE1449020@ziepe.ca> References: Precedence: bulk X-Mailing-List: linux-kernel@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: On Wed, Aug 26, 2026 at 02:29:43PM +0800, Liu Dalin wrote: > While the current callers either pass a valid pointer or explicitly > pass NULL (indicating they don't need the unlock notification), it is > safer to add a defensive NULL check before dereferencing. This prevents > a kernel crash if any caller passes NULL and handle_mm_fault() returns > VM_FAULT_COMPLETED or VM_FAULT_RETRY. > > Fixes smatch warnings: > - mm/gup.c:1597 fixup_user_fault() error: we previously assumed 'unlocked' could be null (see line 1573) It would be better to remove the previous check: if (unlocked) fault_flags |= FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE; And update the kdoc if it is now true that the unlocked parameter cannot be null Jason