Sorry for the late reply. I was away for the long weekend. However, my validation test ran all the way through the long weekend ! So, we can consider this a fix. See the patch attached.
Thanks, Guillaume. Guillaume Autran wrote: > Well, disabling preemption in the get_mmu_context() does not help much... > I'm trying to disable preemption only inside destroy_mmu_context() as > suggested. > Will keep you posted. > > Guillaume. > > > > Marcelo Tosatti wrote: > >>On Thu, Jun 30, 2005 at 09:26:07AM +1000, Benjamin Herrenschmidt wrote: >> >> >>>>Execution is resumed exactly where it has been interrupted. >>>> >>>> >>>> >>>>>The idea behind my patch was to get rid of that nr_free_contexts counter >>>>>that is (I thing) redundant with the context_map. >>>>> >>>>> >>>>Apparently its there to avoid the spinlock exactly on !FEW_CONTEXTS >>>>machines. >>>> >>>>I suppose that what happens is that get_mmu_context() gets preempted after >>>>stealing >>>>a context (so nr_free_contexts = 0), but before setting next_mmu_context to >>>>the >>>>next entry >>>> >>>>next_mmu_context = (ctx + 1) & LAST_CONTEXT; >>>> >>>> >>>Ugh ? Can switch_mm() be preempted at all ? Did I miss yet another >>>"let's open 10 gazillion races for gun" Ingo patch ? >>> >>> >> >>Doh nope it can't - my bad. >> >> >> >>>>So if the now running higher prio tasks calls switch_mm() (which is likely >>>>to happen) >>>>it loops forever on atomic_dec_if_positive(&nr_free_contexts), while >>>>steal_context() >>>>sees "mm->context == CONTEXT". >>>> >>>> >>>I think the race is only when destroy_context() is preempted, but maybe >>>I missed something. >>> >>> >> >>Nope, I think you are right. My "theory" is obviously flawed now. >> >>There seem to be several contexts where destroy_context() could be called >>with preempt enabled - I should have been shutup in the first place :) >> >>Lets wait for Guillaume to test... >> >> >> > >-- >======================================= >Guillaume Autran >Senior Software Engineer >MRV Communications, Inc. >Tel: (978) 952-4932 office >E-mail: gautran at mrv.com >======================================= > >------------------------------------------------------------------------ > >_______________________________________________ >Linuxppc-embedded mailing list >Linuxppc-embedded at ozlabs.org >https://ozlabs.org/mailman/listinfo/linuxppc-embedded > -- ======================================= Guillaume Autran Senior Software Engineer MRV Communications, Inc. Tel: (978) 952-4932 office E-mail: gautran at mrv.com ======================================= -------------- next part -------------- An HTML attachment was scrubbed... URL: http://ozlabs.org/pipermail/linuxppc-embedded/attachments/20050705/c7461bb2/attachment.htm -------------- next part -------------- An embedded and charset-unspecified text was scrubbed... Name: preempt.patch Url: http://ozlabs.org/pipermail/linuxppc-embedded/attachments/20050705/c7461bb2/attachment.txt
