gpiolib: fix the speed of descriptor label setting with SRCU

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Commit 1f2bcb8c8c ("gpio: protect the descriptor label with SRCU")
caused a massive drop in performance of requesting GPIO lines due to the
call to synchronize_srcu() on each label change. Rework the code to not
wait until all read-only users are done with reading the label but
instead atomically replace the label pointer and schedule its release
after all read-only critical sections are done.

To that end wrap the descriptor label in a struct that also contains the
rcu_head struct required for deferring tasks using call_srcu() and stop
using kstrdup_const() as we're required to allocate memory anyway. Just
allocate enough for the label string and rcu_head in one go.

Reported-by: Neil Armstrong <neil.armstrong@linaro.org>
Closes: https://lore.kernel.org/linux-gpio/CAMRc=Mfig2oooDQYTqo23W3PXSdzhVO4p=G4+P8y1ppBOrkrJQ@mail.gmail.com/
Fixes: 1f2bcb8c8c ("gpio: protect the descriptor label with SRCU")
Suggested-by: "Paul E. McKenney" <paulmck@kernel.org>
Tested-by: Neil Armstrong <neil.armstrong@linaro.org> # on SM8650-QRD
Acked-by: "Paul E. McKenney" <paulmck@kernel.org>
Link: https://lore.kernel.org/r/20240507121346.16969-1-brgl@bgdev.pl
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

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This commit is contained in:

Bartosz Golaszewski 2024-05-07 14:13:46 +02:00

parent e67572cd22

commit a86d276930

2 changed files with 30 additions and 8 deletions

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31

drivers/gpio/gpiolib.c

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7

drivers/gpio/gpiolib.h

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