Messages in this thread | | | Date | Mon, 21 Nov 2011 13:52:40 +0530 | From | "Srivatsa S. Bhat" <> | Subject | Re: [PATCH v3] PM/Memory-hotplug: Avoid task freezing failures |
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On 11/21/2011 01:25 PM, Chen Gong wrote: > [...] >> >> Actually, I think I have a better idea based on a key observation: >> We are trying to acquire pm_mutex here. And if we block due to this, >> we are *100% sure* that we are not going to run as long as hibernation >> sequence is running, since hibernation releases pm_mutex only at the >> very end, when everything is done. >> And this means, this task is going to be blocked for much more longer >> than what the freezer intends to achieve. Which means, freezing and >> thawing doesn't really make a difference to this task! >> >> So, let's just ask the freezer to skip freezing us!! And everything >> will be just fine! >> >> Something like: >> >> void lock_system_sleep(void) >> { >> /* simplified freezer_do_not_count() */ >> current->flags |= PF_FREEZER_SKIP; >> >> mutex_lock(&pm_mutex); >> >> } >> >> void unlock_system_sleep(void) >> { >> mutex_unlock(&pm_mutex); >> >> /* simplified freezer_count() */ >> current->flags&= ~PF_FREEZER_SKIP; >> >> } >> >> We probably don't want the restriction that freezer_do_not_count() and >> freezer_count() work only for userspace tasks. So I have open coded >> the relevant parts of those functions here. >> > > This new design looks clean and better than old one. I just curious how do > you design your test environment? e.g. when hibernating is in progress, > try to online some memories and wait for hibernation fails or succeeds? >
Hi Chen,
Thanks a lot for taking a look!
As I have indicated earlier in some of my mails, I am more concerned about the API lock_system_sleep() than memory hotplug, because it is this *API* that is buggy, not memory-hotplug. And going further, any other code planning to use this API will be problematic. So our focus here, is to fix this *API*.
So, to test this API, I have written a kernel module that calls lock_system_sleep() in its init code. Then I load/unload that module wildly in a loop and simultaneously run hibernation tests using the 'pm_test' framework. It is to be also noted that, the issue here is only with the initial steps of hibernation, namely, related to freezer. Hence, pm_test framework fits pretty well to debug these freezer issues. (And in fact, I have found that this method is quite effective to test whether my patch fixes the issue or not.)
Thanks, Srivatsa S. Bhat
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