On 2013-09-22 11:53, Gleb Natapov wrote: > On Sun, Sep 22, 2013 at 10:53:14AM +0200, Paolo Bonzini wrote: >> Il 22/09/2013 09:42, Gleb Natapov ha scritto: >>> On Mon, Sep 16, 2013 at 04:06:10PM +0200, Paolo Bonzini wrote: >>>> Paul Gortmaker reported a BUG on preempt-rt kernels, due to taking the >>>> mmu_lock within the raw kvm_lock in mmu_shrink_scan. He provided a >>>> patch that shrunk the kvm_lock critical section so that the mmu_lock >>>> critical section does not nest with it, but in the end there is no reason >>>> for the vm_list to be protected by a raw spinlock. Only manipulations >>>> of kvm_usage_count and the consequent hardware_enable/disable operations >>>> are not preemptable. >>>> >>>> This small series thus splits the kvm_lock in the "raw" part and the >>>> "non-raw" part. >>>> >>>> Paul, could you please provide your Tested-by? >>>> >>> Reviewed-by: Gleb Natapov <gleb@xxxxxxxxxx> >>> >>> But why should it go to stable? >> >> It is a regression from before the kvm_lock was made raw. Secondarily, > It was made raw in 2.6.39 and commit message claims that it is done for > -rt sake, why regression was noticed only now? Probably, the patch is stressed to infrequently. Just checked: the issue was present from day #1 one, what a shame. > >> it takes a much longer time before a patch hits -rt trees (can even be >> as much as a year) and this patch does nothing on non-rt trees. So >> without putting it into stable it would get no actual coverage. >> > The change is not completely trivial, it splits lock. There is no > obvious problem of course, otherwise you wouldn't send it and I > would ack it :), but it does not mean that the chance for problem is > zero, so why risk stability of stable even a little bit if the patch > does not fix anything in stable? > > I do not know how -rt development goes and how it affects decisions for > stable acceptance, why can't they carry the patch in their tree until > they move to 3.12? I think it would be fair to let stable -rt carry these. -rt requires more specific patching anyway due to the waitqueue issue Paul reported. But CC'ing Steven to obtain his view. Jan -- Siemens AG, Corporate Technology, CT RTC ITP SES-DE Corporate Competence Center Embedded Linux -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
