On Thursday, August 13, 2015 10:39:08 PM Sedat Dilek wrote: > > --f46d04447e7fc2306e051d3753a5 > Content-Type: text/plain; charset=UTF-8 > > On Thu, Aug 13, 2015 at 6:53 PM, Hans de Goede <hdegoede@xxxxxxxxxx> wrote: > > Before this commit, the following would happen: > > > > a) acpi_video_get_backlight_type() gets called > > b) acpi_video_get_backlight_type() calls acpi_video_init_backlight_type() > > c) acpi_video_init_backlight_type() locks its function static init_mutex > > d) acpi_video_init_backlight_type() calls backlight_register_notifier() > > e) backlight_register_notifier() takes its notifier-chain lock > > > > And when the backlight notifier chain gets called we've: > > > > 1) blocking_notifier_call_chain() gets called > > 2) blocking_notifier_call_chain() takes the notifier-chain lock > > 3) blocking_notifier_call_chain() calls acpi_video_backlight_notify() > > 4) acpi_video_backlight_notify() calls acpi_video_get_backlight_type() > > 5) acpi_video_get_backlight_type() calls acpi_video_init_backlight_type() > > 6) acpi_video_init_backlight_type() locks its function static init_mutex > > > > So in the first call sequence we have: > > > > a) init_mutex gets locked > > b) notifier-chain gets locked > > > > and in the second call sequence we have: > > > > 1) notifier-chain gets locked > > 2) init_mutex gets locked > > > > And we've a circular locking dependency. This specific locking dependency > > is fixable without using the big hammer otherwise known as a workqueue, > > but further analysis shows a similar problem with the backlight notifier > > chain lock vs register_count_mutex from drivers/acpi/acpi_video.c, > > and fixing that becomes problematic. > > > > So this commit simply fixes this with the big hammer, performance > > wise this is a non issue as we expect the work to get scheduled > > exactly zero or one times during normal system use. > > > > This patch on top of Linux v4.2-rc6 fixes the issue for me. > > Feel free to add my... > > Reported-by: Sedat Dilek <sedat.dilek@xxxxxxxxx> > Tested-by: Sedat Dilek <sedat.dilek@xxxxxxxxx> Applied, thanks! Rafael -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
