On Tue, Nov 06, 2018 at 10:39:47PM +0100, Ard Biesheuvel wrote: > On 6 November 2018 at 22:34, Will Deacon <will.deacon@xxxxxxx> wrote: > > On Tue, Nov 06, 2018 at 12:37:28PM +0100, Ard Biesheuvel wrote: > >> This series addresses the kexec/kdump crash on arm64 system with many CPUs > >> that was reported by Bhupesh. > >> > >> Patches #1 and #2 fix the actual crash. Patches #3 and #4 optimize the > >> EFI persistent memreserve infrastructure so that fewer memblock reservations > >> are required. > > > > I acked the arm64 part and patches 3 and 4 look good afaict, so: > > > > Acked-by: Will Deacon <will.deacon@xxxxxxx> > > > > for those as well. > > > > The only thing I was wondering is whether or not exhausting the page-sized > > array in the first list entry is rare enough that we could just realloc the > > thing and copy instead of chaining together new pages. That said, without > > seeing the code it's hard to tell whether you save much complexity with such > > a scheme so I'll leave it up to you. > > > > Well, the problem is that the page-sized array may have been allocated > by a previous kernel, and so it may be memblock_reserve()d already, in > which case reallocating does not actually free up the memory in a > useful way. > > Also, in the unlikely event that we race and allocate two new pages at > the same time, the current scheme will not break (and we will > ultimately fill up all the slots in both pages before allocating even > more pages). This will become a lot trickier if we do reallocation. Ah crap, yeah, the concurrency angle makes that really awful. Thanks. > So if the current approach looks correct to you, then I'd prefer to > stick with it. > > Do you agree with applying #3 and #4 as fixes? If Patch 1 alone is sufficient to solve the issue for Bhupesh, then I don't think we have a need to treat 3 and 4 as fixes (and therefore we can avoid having to backport them to stable kernels). Will
