Hi Shimoda-san,
On Tue, Mar 12, 2019 at 4:17 AM Yoshihiro Shimoda
<yoshihiro.shimoda.uh@xxxxxxxxxxx> wrote:
> From: Phong Hoang <phong.hoang.wz@xxxxxxxxxxx>
>
> This patch fixes deadlock warning if removing PWM device
> when CONFIG_PROVE_LOCKING is enabled.
>
> This issue can be reproceduced by the following steps on
> the R-Car H3 Salvator-X board if the backlight is disabled:
>
> # cd /sys/class/pwm/pwmchip0
> # echo 0 > export
> # ls
> device export npwm power pwm0 subsystem uevent unexport
> # cd device/driver
> # ls
> bind e6e31000.pwm uevent unbind
> # echo e6e31000.pwm > unbind
>
> [ 87.659974] ======================================================
> [ 87.666149] WARNING: possible circular locking dependency detected
> [ 87.672327] 5.0.0 #7 Not tainted
[...]
> This warning occurs because pwmchip_remove still keeps pwm_lock
> when removing sysfs. That's why it leads to that conflict.
> Hence, this patch unlocks pwm_lock before removing sysfs.
> Also, pwmchip_sysfs_export() doesn't seem to need the pwm_lock
> held so that to achieve consistance between export and
> unexport this patch also modifies it.
>
> Signed-off-by: Phong Hoang <phong.hoang.wz@xxxxxxxxxxx>
> [shimoda: revise the commit log and code]
> Fixes: 76abbdde2d95 ("pwm: Add sysfs interface")
> Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@xxxxxxxxxxx>
> Tested-by: Hoan Nguyen An <na-hoan@xxxxxxxxxxx>
Thanks for your patch!
Looks good to me: class_find_device() seems to use its own locking in
the class to protect against concurrent modification.
Reviewed-by: Geert Uytterhoeven <geert+renesas@xxxxxxxxx>
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
