| Message ID | 20221229161948.594102-1-brgl@bgdev.pl |
|---|---|
| Headers | show |
| Series | tty: serial: add and use a managed variant of uart_add_one_port() | expand |
On Thu, Dec 29, 2022 at 05:19:46PM +0100, Bartosz Golaszewski wrote: > From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org> > > Resending rebased on top of v6.2-rc1 > > -- > > This series adds a managed variant of uart_add_one_port() and uses it in the > qcom-geni-serial driver. > > I've been asked by Greg to send it separately and he didn't seem to be > impressed by the proposition of adding devres interfaces to the tty layer > in general. I can only assume it has something to do with the ongoing > discussion about the supposed danger of using devres interfaces in conjunction > with exporting character devices to user-space. That is correct. > The bug in question can be triggered by opening a device file, unbinding the > driver that exported it and then calling any of the system calls on the > associated file descriptor. > > After some testing I noticed that many subsystems are indeed either crashing > or deadlocking in the above situation. I've sent patches that attempt to fix > the GPIO and I2C subsystems[1][2]. Neither of these issues have anything to > do with devres and all to do with the fact that certain resources are freed > on driver unbind and others need to live for as long as the character device > exists. More details on that in the cover letters and commit messages in the > links. > > I'd like to point out that the serial code is immune to this issue as before > every operation, the serial core takes the port lock and checks the uart > state. If the device no longer exists (when the uart port is removed, the > pointer to uart_port inside uart_state is to NULL), it gracefully returns > -ENODEV to user-space. > > Please consider applying the patches in the series as devres is the easiest > way to lessen the burden on driver developers when dealing with complex error > paths and resource leaks. The general rule for devres is: if it can be freed > in .remove() then it can be managed by devres, which is the case for this new > helper. Overall you are adding more code to the kernel than removing, so how is this a win? Perhaps if other drivers were converted over to this new function then I would be more inclined to be able to accept it. But as-is, with only one user, it's a non-starter, sorry. thanks, greg k-h
From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org> Resending rebased on top of v6.2-rc1 -- This series adds a managed variant of uart_add_one_port() and uses it in the qcom-geni-serial driver. I've been asked by Greg to send it separately and he didn't seem to be impressed by the proposition of adding devres interfaces to the tty layer in general. I can only assume it has something to do with the ongoing discussion about the supposed danger of using devres interfaces in conjunction with exporting character devices to user-space. The bug in question can be triggered by opening a device file, unbinding the driver that exported it and then calling any of the system calls on the associated file descriptor. After some testing I noticed that many subsystems are indeed either crashing or deadlocking in the above situation. I've sent patches that attempt to fix the GPIO and I2C subsystems[1][2]. Neither of these issues have anything to do with devres and all to do with the fact that certain resources are freed on driver unbind and others need to live for as long as the character device exists. More details on that in the cover letters and commit messages in the links. I'd like to point out that the serial code is immune to this issue as before every operation, the serial core takes the port lock and checks the uart state. If the device no longer exists (when the uart port is removed, the pointer to uart_port inside uart_state is to NULL), it gracefully returns -ENODEV to user-space. Please consider applying the patches in the series as devres is the easiest way to lessen the burden on driver developers when dealing with complex error paths and resource leaks. The general rule for devres is: if it can be freed in .remove() then it can be managed by devres, which is the case for this new helper. Bart [1] https://lkml.org/lkml/2022/12/8/826 [2] https://lkml.org/lkml/2022/12/5/414 Bartosz Golaszewski (2): tty: serial: provide devm_uart_add_one_port() tty: serial: qcom-geni-serial: use devres for uart port management .../driver-api/driver-model/devres.rst | 3 ++ drivers/tty/serial/qcom_geni_serial.c | 8 +--- drivers/tty/serial/serial_core.c | 48 +++++++++++++++++++ include/linux/serial_core.h | 6 +++ 4 files changed, 58 insertions(+), 7 deletions(-)