On Friday, August 14, 2015 11:36:41 AM Sedat Dilek wrote: > On Fri, Aug 14, 2015 at 11:39 AM, Rafael J. Wysocki <rjw@xxxxxxxxxxxxx> wrote: > > 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! > > > > Thanks for carrying this one. > Isn't this a for-4.2/acpi-video-fixes? I have no branch like that. > Why did you apply this in your linux-next Git branch? Because that's what I do normally with patches I'm going to push to Linus. 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
