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Date: Thu, 22 Mar 2007 01:16:23 +0200 From: Maxim <maximlevitsky@...il.com> To: nigel@...el.suspend2.net Cc: "Rafael J. Wysocki" <rjw@...k.pl>, linux-kernel@...r.kernel.org, Pavel Machek <pavel@....cz>, "Rafael J. Wysocki" <rjw@...k.pl> Subject: Re: [BUG] Code reordering in swsusp breaks suspend on SMP systems On Thursday 22 March 2007 01:14:05 Maxim wrote: > On Wednesday 21 March 2007 23:22:40 Nigel Cunningham wrote: > > Hi. > > > > On Wed, 2007-03-21 at 18:40 +0200, Maxim Levitsky wrote: > > > Hi, > > > > > > Starting with 2.6.21-rc1 suspend to ram and disk doesn't work anymore on my system. > > > > > > I did a git-bisect and found that those commits break it: > > > > > > e3c7db621bed4afb8e231cb005057f2feb5db557 - [PATCH] [PATCH] PM: Change code ordering in main.c > > > ed746e3b18f4df18afa3763155972c5835f284c5 - [PATCH] [PATCH] swsusp: Change code ordering in disk.c > > > 259130526c267550bc365d3015917d90667732f1 - [PATCH] [PATCH] swsusp: Change code ordering in user.c > > > > > > I already reported about it, but now i know the reason why suspend breaks. > > > > > > The problem is that both cpu_up/cpu_down were allowed to sleep until now, > > > and it did work because those functions could be called only in process context > > > (the one that writes to /sys/devices/system/cpu/cpu*/online) or idle thread that does smp_init()). > > > > > > But now they are called _after_ all tasks were suspended, so if cpu_down tries for example to take a lock > > > that is taken by different process, it can't since the different proccess is frozen and can't release the lock. > > > > > > I tested this and all results are positive: > > > > > > I disabled 2nd cpu by hand, and then suspend to ram was successfull. > > > Suspend to disk went correctly, but it hang on resume, and I know why. > > > It hang in old kernel trying to disable 2nd cpu that was enabled by it. > > > > > > I was able using kdb to confirm that this is true because it was still possible to enter kdb, and see that > > > idle thread (swapper) was active, and uswsusp was waiting on mutex inside workqueue_cpu_callback. > > > > > > The solution for this problem seems to be ether complete audit of code that uses register_cpu_notifier, > > > to ensure that it doesn't sleep. > > > Also documentation should be changed to note about it. > > > > > > Or, it is also possible to revert this change. > > > > Do you know exactly which mutex was being waited on and where it was > > taken? If you can say that, it would be much more helpful. > > > > Regards, > > > > Nigel > > > > > > Hello, > > It is workqueue_mutex > and it is taken in kernel/workqueue.c:797 > > this is guilt of freezable work queues , and XFS uses it (and I use XFS) > > Thanks to Rafael J. Wysocki for pointing it out to me. > > Regards, > Maxim Levitsky > oops, Forgot to cc Regards, Maxim Levitsky - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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