On Wed, 3 Apr 2024 at 18:02, Sasha Levin <sashal@xxxxxxxxxx> wrote: > > This is a note to let you know that I've just added the patch titled > > gpio: protect the list of GPIO devices with SRCU > > to the 6.8-stable tree which can be found at: > http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary > > The filename of the patch is: > gpio-protect-the-list-of-gpio-devices-with-srcu.patch > and it can be found in the queue-6.8 subdirectory. > > If you, or anyone else, feels it should not be added to the stable tree, > please let <stable@xxxxxxxxxxxxxxx> know about it. > > > > commit 077106f97c7d113ebacb00725d83b817d0e89288 > Author: Bartosz Golaszewski <bartosz.golaszewski@xxxxxxxxxx> > Date: Fri Jan 19 16:43:13 2024 +0100 > > gpio: protect the list of GPIO devices with SRCU > > [ Upstream commit e348544f7994d252427ed3ae637c7081cbb90f66 ] > > We're working towards removing the "multi-function" GPIO spinlock that's > implemented terribly wrong. We tried using an RW-semaphore to protect > the list of GPIO devices but it turned out that we still have old code > using legacy GPIO calls that need to translate the global GPIO number to > the address of the associated descriptor and - to that end - traverse > the list while holding the lock. If we change the spinlock to a sleeping > lock then we'll end up with "scheduling while atomic" bugs. > > Let's allow lockless traversal of the list using SRCU and only use the > mutex when modyfing the list. > > While at it: let's protect the period between when we start the lookup > and when we finally request the descriptor (increasing the reference > count of the GPIO device) with the SRCU read lock. > > Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@xxxxxxxxxx> > Reviewed-by: Linus Walleij <linus.walleij@xxxxxxxxxx> > Acked-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx> > Stable-dep-of: 5c887b65bbd1 ("gpiolib: Fix debug messaging in gpiod_find_and_request()") > Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> > I'm not sure what the reason for picking this up into stable was but I believe it's not a good idea. This is just the first patch in a big series[1] of 24 commits total on top of which we had several bug fixes during the stabilization phase in next. Without the rest of the rework, it doesn't really improve the situation a lot. I suggest dropping this and not trying to backport any of the GPIOLIB locking rework to stable branches. Best Regards, Bartosz [1] https://lore.kernel.org/lkml/20240208095920.8035-22-brgl@xxxxxxxx/T/
