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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-439f820a2f1sm5725154f8f.30.2026.03.11.03.47.37 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 11 Mar 2026 03:47:38 -0700 (PDT) Date: Wed, 11 Mar 2026 10:47:36 +0000 From: David Laight To: Christian Brauner Cc: Linus Torvalds , linux-kernel@vger.kernel.org, linux-modules@vger.kernel.org, linux-nfs@vger.kernel.org, bpf@vger.kernel.org, kunit-dev@googlegroups.com, linux-doc@vger.kernel.org, linux-trace-kernel@vger.kernel.org, netfs@lists.linux.dev, io-uring@vger.kernel.org, audit@vger.kernel.org, rcu@vger.kernel.org, kvm@vger.kernel.org, virtualization@lists.linux.dev, netdev@vger.kernel.org, linux-mm@kvack.org, linux-security-module@vger.kernel.org, Christian Loehle , linux-fsdevel@vger.kernel.org Subject: Re: [PATCH v2 1/2] kthread: remove kthread_exit() Message-ID: <20260311104736.51b53405@pumpkin> In-Reply-To: <20260310-work-kernel-exit-v2-1-30711759d87b@kernel.org> References: <20260310-work-kernel-exit-v2-0-30711759d87b@kernel.org> <20260310-work-kernel-exit-v2-1-30711759d87b@kernel.org> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) Precedence: bulk X-Mailing-List: linux-security-module@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Tue, 10 Mar 2026 15:56:09 +0100 Christian Brauner wrote: > In 28aaa9c39945 ("kthread: consolidate kthread exit paths to prevent use-after-free") > we folded kthread_exit() into do_exit() when we fixed a nasty UAF bug. > We left kthread_exit() around as an alias to do_exit(). Remove it > completely. ... > -#define module_put_and_kthread_exit(code) kthread_exit(code) > +#define module_put_and_kthread_exit(code) do_exit(code) I'm intrigued... How does that actually know to do the module_put()? (I know it does one - otherwise my driver wouldn't unload.) The corresponding try_module_get(THIS_MODULE) is done before the kthread_run() (and has to be 'put' if that fails). So there is an explicit 'get' but an implicit 'put'. While a loadable module that creates a kthread usually needs to give the kthread a reference to its module and then have that reference released as the kthread exits, I can imagine cases where that isn't true. (Or broken code that just hopes the module won't be unloaded just as the kthread exits.) It actually makes me think that module_put_and_exit() ought to have a 'module' parameter. Or, perhaps, kthread_create() should have the module parameter and hold a reference to that module until it exits. David