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[14.200.229.209]) by smtp.gmail.com with ESMTPSA id b29-20020aa7951d000000b0056d98e31439sm7484888pfp.140.2022.11.08.21.12.04 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 08 Nov 2022 21:12:06 -0800 (PST) Date: Wed, 9 Nov 2022 13:12:01 +0800 From: Kent Gibson To: Zeng Heng Cc: linus.walleij@linaro.org, brgl@bgdev.pl, liwei391@huawei.com, linux-gpio@vger.kernel.org Subject: Re: [PATCH] gpiolib: fix memory leak in gpiochip_setup_dev Message-ID: References: <20221108115324.270361-1-zengheng4@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-gpio@vger.kernel.org On Wed, Nov 09, 2022 at 12:57:48AM +0800, Kent Gibson wrote: > On Tue, Nov 08, 2022 at 07:53:24PM +0800, Zeng Heng wrote: > > gcdev_register & gcdev_unregister call device_add & device_del to > > request/release source. But in device_add, the dev->p allocated by > > device_private_init is not released by device_del. > > > > So when calling gcdev_unregister to release gdev, it needs put_device > > to release dev in the following. > > > > Otherwise, kmemleak would report memory leak such as below: > > > > unreferenced object 0xffff88810b406400 (size 512): > > comm "python3", pid 1682, jiffies 4295346908 (age 24.090s) > > hex dump (first 32 bytes): > > 00 00 00 00 ad 4e ad de ff ff ff ff 00 00 00 00 .....N.......... > > ff ff ff ff ff ff ff ff a0 5e 23 90 ff ff ff ff .........^#..... > > backtrace: > > [<00000000a58ee5fe>] kmalloc_trace+0x22/0x110 > > [<0000000045fe2058>] device_add+0xb34/0x1130 > > [<00000000d778b45f>] cdev_device_add+0x83/0xe0 > > [<0000000089f948ed>] gpiolib_cdev_register+0x73/0xa0 > > [<00000000a3a8a316>] gpiochip_setup_dev+0x1c/0x70 > > [<00000000787227b4>] gpiochip_add_data_with_key+0x10f6/0x1bf0 > > [<000000009ac5742c>] devm_gpiochip_add_data_with_key+0x2e/0x80 > > [<00000000bf2b23d9>] xra1403_probe+0x192/0x1b0 [gpio_xra1403] > > [<000000005b5ef2d4>] spi_probe+0xe1/0x140 > > [<000000002b26f6f1>] really_probe+0x17c/0x3f0 > > [<00000000dd2dad9c>] __driver_probe_device+0xe3/0x170 > > [<000000005ca60d2a>] device_driver_attach+0x34/0x80 > > [<00000000e9db90db>] bind_store+0x10b/0x1a0 > > [<00000000e2650f8a>] drv_attr_store+0x49/0x70 > > [<0000000080a80b2b>] sysfs_kf_write+0x8c/0xb0 > > [<00000000a28b45b9>] kernfs_fop_write_iter+0x216/0x2e0 > > > > unreferenced object 0xffff888100de9800 (size 512): > > comm "python3", pid 264, jiffies 4294737615 (age 33.514s) > > hex dump (first 32 bytes): > > 00 00 00 00 ad 4e ad de ff ff ff ff 00 00 00 00 .....N.......... > > ff ff ff ff ff ff ff ff a0 5e 63 a1 ff ff ff ff .........^c..... > > backtrace: > > [<00000000bcc571d0>] kmalloc_trace+0x22/0x110 > > [<00000000eeb06124>] device_add+0xb34/0x1130 > > [<000000007e5cd2fd>] cdev_device_add+0x83/0xe0 > > [<000000008f6bcd3a>] gpiolib_cdev_register+0x73/0xa0 > > [<0000000012c93b24>] gpiochip_setup_dev+0x1c/0x70 > > [<00000000a24b646a>] gpiochip_add_data_with_key+0x10f6/0x1bf0 > > [<000000000c225212>] tpic2810_probe+0x16e/0x196 [gpio_tpic2810] > > [<00000000b52d04ff>] i2c_device_probe+0x651/0x680 > > [<0000000058d3ff6b>] really_probe+0x17c/0x3f0 > > [<00000000586f43d3>] __driver_probe_device+0xe3/0x170 > > [<000000003f428602>] device_driver_attach+0x34/0x80 > > [<0000000040e91a1b>] bind_store+0x10b/0x1a0 > > [<00000000c1d990b9>] drv_attr_store+0x49/0x70 > > [<00000000a23bfc22>] sysfs_kf_write+0x8c/0xb0 > > [<00000000064e6572>] kernfs_fop_write_iter+0x216/0x2e0 > > [<00000000026ce093>] vfs_write+0x658/0x810 > > > > Because at the point of gpiochip_setup_dev here, where dev.release > > does not set yet, calling put_device would cause the warning of > > no release function and double-free in the following fault handler > > route (when kfree dev_name). So directly calling kfree to release > > dev->p here in case of memory leak. > > > > Fixes: 1f5eb8b17f02 ("gpiolib: fix sysfs when cdev is not selected") > > I'm confused. You say "gcdev_register & gcdev_unregister call device_add > & device_del" - which is only the case when CONFIG_GPIO_CDEV is not set. > > But your trace shows CONFIG_GPIO_CDEV is set, as otherwise > gpiolib_cdev_register() would not exist. > > Can you clarify the configuration in which you are seeing the problem? > > Assuming CONFIG_GPIO_CDEV is NOT set: > > Provide a more appropriate trace. > > From a reading of the device_add() documentation, there is a problem if > the device_add() fails - in that case put_device() should be called - and > it is not, instead gpiochip_setup_dev() returns immediately - not going > via the err_remove_device path where your fix is??. > The correct fix for that would be to change the gcdev_register() to call > put_device() if device_add() fails. > Ignore that - as you mentioned the dev.release hasn't been set at that point. Having another look at this, I don't think the problem is related to the Fixed commit at all - it looks more general. How did you conclude that that commit introduced the problem? Is it easily repeatable and have you bisected for it? Cheers, Kent.