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[188.155.181.108]) by smtp.gmail.com with ESMTPSA id cc21-20020a0564021b9500b00403bc1dfd5csm6063924edb.85.2022.02.28.03.30.46 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 28 Feb 2022 03:30:47 -0800 (PST) Message-ID: Date: Mon, 28 Feb 2022 12:30:45 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.5.0 Subject: Re: [PATCH v3 01/11] driver: platform: Add helper for safer setting of driver_override Content-Language: en-US To: Abel Vesa Cc: Greg Kroah-Hartman , "Rafael J. Wysocki" , Stuart Yoder , Laurentiu Tudor , Shawn Guo , Sascha Hauer , Fabio Estevam , "K. Y. Srinivasan" , Haiyang Zhang , Stephen Hemminger , Wei Liu , Dexuan Cui , Bjorn Helgaas , Bjorn Andersson , Mathieu Poirier , Vineeth Vijayan , Peter Oberparleiter , Heiko Carstens , Vasily Gorbik , Alexander Gordeev , Christian Borntraeger , Sven Schnelle , Andy Gross , Srinivas Kandagatla , Mark Brown , "Michael S. Tsirkin" , Jason Wang , linux-kernel@vger.kernel.org, linux-clk@vger.kernel.org, NXP Linux Team , linux-arm-kernel@lists.infradead.org, linux-hyperv@vger.kernel.org, linux-pci@vger.kernel.org, linux-remoteproc@vger.kernel.org, linux-s390@vger.kernel.org, linux-arm-msm@vger.kernel.org, alsa-devel@alsa-project.org, linux-spi@vger.kernel.org, virtualization@lists.linux-foundation.org, Linus Torvalds , Rasmus Villemoes References: <20220227135214.145599-1-krzysztof.kozlowski@canonical.com> <20220227135214.145599-2-krzysztof.kozlowski@canonical.com> From: Krzysztof Kozlowski In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 28/02/2022 11:51, Abel Vesa wrote: > On 22-02-27 14:52:04, Krzysztof Kozlowski wrote: >> Several core drivers and buses expect that driver_override is a >> dynamically allocated memory thus later they can kfree() it. >> >> However such assumption is not documented, there were in the past and >> there are already users setting it to a string literal. This leads to >> kfree() of static memory during device release (e.g. in error paths or >> during unbind): >> >> kernel BUG at ../mm/slub.c:3960! >> Internal error: Oops - BUG: 0 [#1] PREEMPT SMP ARM >> ... >> (kfree) from [] (platform_device_release+0x88/0xb4) >> (platform_device_release) from [] (device_release+0x2c/0x90) >> (device_release) from [] (kobject_put+0xec/0x20c) >> (kobject_put) from [] (exynos5_clk_probe+0x154/0x18c) >> (exynos5_clk_probe) from [] (platform_drv_probe+0x6c/0xa4) >> (platform_drv_probe) from [] (really_probe+0x280/0x414) >> (really_probe) from [] (driver_probe_device+0x78/0x1c4) >> (driver_probe_device) from [] (bus_for_each_drv+0x74/0xb8) >> (bus_for_each_drv) from [] (__device_attach+0xd4/0x16c) >> (__device_attach) from [] (bus_probe_device+0x88/0x90) >> (bus_probe_device) from [] (device_add+0x3dc/0x62c) >> (device_add) from [] (of_platform_device_create_pdata+0x94/0xbc) >> (of_platform_device_create_pdata) from [] (of_platform_bus_create+0x1a8/0x4fc) >> (of_platform_bus_create) from [] (of_platform_bus_create+0x20c/0x4fc) >> (of_platform_bus_create) from [] (of_platform_populate+0x84/0x118) >> (of_platform_populate) from [] (of_platform_default_populate_init+0xa0/0xb8) >> (of_platform_default_populate_init) from [] (do_one_initcall+0x8c/0x404) >> (do_one_initcall) from [] (kernel_init_freeable+0x3d0/0x4d8) >> (kernel_init_freeable) from [] (kernel_init+0x8/0x114) >> (kernel_init) from [] (ret_from_fork+0x14/0x20) >> >> Provide a helper which clearly documents the usage of driver_override. >> This will allow later to reuse the helper and reduce amount of >> duplicated code. >> >> Convert the platform driver to use new helper and make the >> driver_override field const char (it is not modified by the core). >> >> Signed-off-by: Krzysztof Kozlowski >> --- >> drivers/base/driver.c | 51 +++++++++++++++++++++++++++++++++ >> drivers/base/platform.c | 28 +++--------------- >> include/linux/device/driver.h | 2 ++ >> include/linux/platform_device.h | 7 ++++- >> 4 files changed, 63 insertions(+), 25 deletions(-) >> >> diff --git a/drivers/base/driver.c b/drivers/base/driver.c >> index 8c0d33e182fd..353750b0bbc5 100644 >> --- a/drivers/base/driver.c >> +++ b/drivers/base/driver.c >> @@ -30,6 +30,57 @@ static struct device *next_device(struct klist_iter *i) >> return dev; >> } >> >> +/** >> + * driver_set_override() - Helper to set or clear driver override. >> + * @dev: Device to change >> + * @override: Address of string to change (e.g. &device->driver_override); >> + * The contents will be freed and hold newly allocated override. >> + * @s: NUL terminated string, new driver name to force a match, pass empty >> + * string to clear it >> + * @len: length of @s >> + * >> + * Helper to set or clear driver override in a device, intended for the cases >> + * when the driver_override field is allocated by driver/bus code. >> + * >> + * Returns: 0 on success or a negative error code on failure. >> + */ >> +int driver_set_override(struct device *dev, const char **override, >> + const char *s, size_t len) > > TBH, I think it would make more sense to have this generic > driver_set_override receive only the dev and the string. And then, > each bus type will have their own implementation that handle things > their own way. This would allow all the drivers that will use this to > do something like this: > > ret = driver_set_override(&pdev->dev, "override_string"); > > I think it would look more cleaner. > The interface in general is not for the drivers. Drivers use it in exceptions (few cases in entire kernel) but many times they actually do not need to. Adding a dedicated driver_set_override() brings intention that such usage is welcomed... but it's not. :) Best regards, Krzysztof