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 [<c058da50>] (platform_device_release+0x88/0xb4) >> (platform_device_release) from [<c0585be0>] (device_release+0x2c/0x90) >> (device_release) from [<c0a69050>] (kobject_put+0xec/0x20c) >> (kobject_put) from [<c0f2f120>] (exynos5_clk_probe+0x154/0x18c) >> (exynos5_clk_probe) from [<c058de70>] (platform_drv_probe+0x6c/0xa4) >> (platform_drv_probe) from [<c058b7ac>] (really_probe+0x280/0x414) >> (really_probe) from [<c058baf4>] (driver_probe_device+0x78/0x1c4) >> (driver_probe_device) from [<c0589854>] (bus_for_each_drv+0x74/0xb8) >> (bus_for_each_drv) from [<c058b48c>] (__device_attach+0xd4/0x16c) >> (__device_attach) from [<c058a638>] (bus_probe_device+0x88/0x90) >> (bus_probe_device) from [<c05871fc>] (device_add+0x3dc/0x62c) >> (device_add) from [<c075ff10>] (of_platform_device_create_pdata+0x94/0xbc) >> (of_platform_device_create_pdata) from [<c07600ec>] (of_platform_bus_create+0x1a8/0x4fc) >> (of_platform_bus_create) from [<c0760150>] (of_platform_bus_create+0x20c/0x4fc) >> (of_platform_bus_create) from [<c07605f0>] (of_platform_populate+0x84/0x118) >> (of_platform_populate) from [<c0f3c964>] (of_platform_default_populate_init+0xa0/0xb8) >> (of_platform_default_populate_init) from [<c01031f8>] (do_one_initcall+0x8c/0x404) >> (do_one_initcall) from [<c0f012c0>] (kernel_init_freeable+0x3d0/0x4d8) >> (kernel_init_freeable) from [<c0a7def0>] (kernel_init+0x8/0x114) >> (kernel_init) from [<c01010b4>] (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 <krzysztof.kozlowski@xxxxxxxxxxxxx> >> --- >> 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
