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Tue, 24 Mar 2026 07:56:18 -0700 (PDT) From: Felix Gu To: Mark Brown , Andy Shevchenko Cc: linux-spi@vger.kernel.org, linux-kernel@vger.kernel.org, Felix Gu Subject: Re: [PATCH v1 1/1] spi: Simplify devm_spi_*_controller() Date: Tue, 24 Mar 2026 22:55:48 +0800 Message-ID: <20260324145548.139952-1-ustc.gu@gmail.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <176797260995.67850.318976521283878747.b4-ty@kernel.org> References: <176797260995.67850.318976521283878747.b4-ty@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit > /** > @@ -3398,22 +3395,14 @@ static void devm_spi_unregister(struct device *dev, void *res) > int devm_spi_register_controller(struct device *dev, > struct spi_controller *ctlr) > { > - struct spi_controller **ptr; > int ret; > > - ptr = devres_alloc(devm_spi_unregister, sizeof(*ptr), GFP_KERNEL); > - if (!ptr) > - return -ENOMEM; > - > ret = spi_register_controller(ctlr); > - if (!ret) { > - *ptr = ctlr; > - devres_add(dev, ptr); > - } else { > - devres_free(ptr); > - } > + if (ret) > + return ret; > + > + return devm_add_action_or_reset(dev, devm_spi_unregister_controller, ctlr); > > - return ret; > } > EXPORT_SYMBOL_GPL(devm_spi_register_controller); Hi Andy and Mark, It seems has a potential corner case in this commit. The issue is that devm_add_action_or_reset() triggers its callback immediately if the internal devres allocation fails. This creates the following sequence: 1. spi_register_controller(ctlr) succeeds. 2. devm_add_action_or_reset() is called but fails. 3. The "reset" triggers devm_spi_unregister_controller(ctlr) immediately. 4. This calls spi_unregister_controller(ctlr). 5. For controllers allocated via spi_alloc_host() (where ctlr->devm_allocated is false), spi_unregister_controller() calls put_device(&ctlr->dev). 6. This drops the reference count to zero and frees the ctlr structure. However, the driver still holds the ctlr pointer and will typically attempt its own cleanup, leading to a use-after-free or double-free. What are your thoughts on this? Does this analysis seem correct, or am I missing a detail in how the refcounting is handled here? Best regards, Felix