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Date: Tue, 31 Jan 2012 05:39:00 +0530 From: "Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com> To: Tejun Heo <tj@...nel.org> CC: rjw@...k.pl, pavel@....cz, len.brown@...el.com, linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH v2 2/4] PM/Freezer: Make thaw_processes() thaw only userspace tasks On 01/31/2012 05:00 AM, Tejun Heo wrote: > On Tue, Jan 31, 2012 at 04:44:48AM +0530, Srivatsa S. Bhat wrote: >> Currently the situation is: >> >> freeze_processes() - freezes only userspace tasks >> freeze_kernel_threads() - freezes only kernel threads >> thaw_kernel_threads() - thaws only kernel threads >> thaw_processes() - thaws *everything* (both userspace tasks and kernel threads) > > Umm... I don't really get this. Why is this a problem? The list is > not even correct. freeze_kernel_threads() doesn't freeze "only" > kernel threads. It freezes all threads "including" kernel threads and Oh, you are are right - the list is incorrect. I guess I got carried away thinking about thaw_kernel_threads(). > that's only natural because you can't freeze kernel threads without > freezing userland threads and of course you can't thaw userland > threads without thawing kernel threads. > > The system simply won't work if you do it otherwise and making them > disjoint operations increases the chance of bugs. These operations > are naturally enclosed within each other and trying to break them > apart isn't a good idea. > Yeah, I get it now.. Thanks for the explanation! > What's the problem you're trying to solve here? I don't really see > code clean up. Code is different but not necessarily cleaner and FWIW > it seems more unnatural and brittle to me. > The thing is that, I wanted to avoid a bug in the patch posted at https://lkml.org/lkml/2012/1/29/47 as explained in the link. So I guess I should have simply done: freeze_kernel_threads() calls thaw_kernel_threads() upon error. The caller of freeze_kernel_threads() will call thaw_processes() if necessary. This way even the SNAPSHOT_CREATE_IMAGE ioctl would remain safe. I'll think it through again and post an updated patch. Thank you very much for the review! Regards, Srivatsa S. Bhat -- 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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