Messages in this thread | | | Date | Wed, 14 Mar 2012 16:17:26 -0700 | From | Stephen Boyd <> | Subject | Re: [PATCH] firmware loader: don't cancel _nowait requests when helper is not yet available |
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On 03/14/12 16:13, Rafael J. Wysocki wrote: > On Thursday, March 15, 2012, Rafael J. Wysocki wrote: >> On Wednesday, March 14, 2012, Stephen Boyd wrote: >>> On 03/13/12 13:14, Rafael J. Wysocki wrote: >>>> All of those use cases are in fact of the "wait for user space to be thawed >>>> and then load the firmware" type, which I believe may be handled without >>>> changing that code. >>>> >>>> Why don't you make your kthread freezable, for one example? >>>> >>>> Why don't you use a freezable workqueue instead? >>>> >>> If we put it on the freezable workqueue or make it a freezable thread >>> will it work? >> That depends on what exactly you want to achieve, which isn't entirely clear >> to me at this point. >> >>> In my scenario a wakeup interrupt comes in that wakes us up from >>> suspend. Within that wakeup handler a work item is scheduled to the >>> freezable workqueue. That work item then calls request_firmware(). >> That should work. >> >>> It looks like we call schedule() after thawing the workqueues and tasks >>> so the work item could run before usermodehelpers are enabled and then >>> request_firmware() would fail. Do we need something like this (ignore >>> the fact that we call usermodhelper_enable() twice)? >>> >>> diff --git a/kernel/power/process.c b/kernel/power/process.c >>> index 7e42645..61bfa95 100644 >>> --- a/kernel/power/process.c >>> +++ b/kernel/power/process.c >>> @@ -187,6 +187,7 @@ void thaw_processes(void) >>> } while_each_thread(g, p); >>> read_unlock(&tasklist_lock); >>> >>> + usermodehelper_enable(); >> That would be a reasonable change. >> >>> schedule(); >>> printk("done.\n"); >>> } >>> >>> >>> Is there a reason we disable usermodehelpers if >>> CONFIG_SUSPEND_FREEZER=n? >> Not really, but CONFIG_SUSPEND_FREEZER=n can only work reliably in a >> very limited set of cases, so I don't think it's even worth making the >> general code depend on it. >> >> I'd actually prefer to remove CONFIG_SUSPEND_FREEZER altogether, >> because it's not very useful nowadays (probably isn't useful at all). >> >>> Should we do this instead so that >>> usermodehelpers are only disabled if we freeze userspace? Also what is >>> that schedule() call in thaw_kernel_threads() for? It looks like we'll >>> call schedule between kernel thread thawing and userspace thawing. >> Which is OK, I think. > Moreover, thaw_kernel_threads() is _only_ called by (a) freeze_kernel_threads() > on error and (b) user-space hibernate interface in kernel/power/user.c > (and please read the comment in there describing what it's there for, which > also explains why the schedule() call in there is necessary).
Exactly. So in case (a) when the error occurs we'll have this call flow:
usermodehelpers_disable() suspend_freeze_processes() freeze_processes() freeze_kernel_threads() try_to_freeze_tasks() <-- returns error thaw_kernel_threads() schedule() thaw_processes() usermodehelpers_enable()
Shouldn't we schedule only after we thaw all processes (not just tasks)? Otherwise we may run a kernel thread before userspace is thawed?
-- Sent by an employee of the Qualcomm Innovation Center, Inc. The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.
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