On 16/09/2020 17:30, Mike Kravetz wrote: > On 9/16/20 2:14 AM, Song Bao Hua (Barry Song) wrote: >>>> -----Original Message----- >>>> From: Mike Kravetz [mailto:mike.kravetz@xxxxxxxxxx] >>>> Sent: Wednesday, September 16, 2020 8:57 AM >>>> To: linux-mm@xxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; >>>> linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; linux-mips@xxxxxxxxxxxxxxx >>>> Cc: Roman Gushchin <guro@xxxxxx>; Song Bao Hua (Barry Song) >>>> <song.bao.hua@xxxxxxxxxxxxx>; Mike Rapoport <rppt@xxxxxxxxxx>; Joonsoo >>>> Kim <js1304@xxxxxxxxx>; Rik van Riel <riel@xxxxxxxxxxx>; Aslan Bakirov >>>> <aslan@xxxxxx>; Michal Hocko <mhocko@xxxxxxxxxx>; Andrew Morton >>>> <akpm@xxxxxxxxxxxxxxxxxxxx>; Mike Kravetz <mike.kravetz@xxxxxxxxxx> >>>> Subject: [PATCH] cma: make number of CMA areas dynamic, remove >>>> CONFIG_CMA_AREAS >>>> >>>> The number of distinct CMA areas is limited by the constant >>>> CONFIG_CMA_AREAS. In most environments, this was set to a default >>>> value of 7. Not too long ago, support was added to allocate hugetlb >>>> gigantic pages from CMA. More recent changes to make >>> dma_alloc_coherent >>>> NUMA-aware on arm64 added more potential users of CMA areas. Along >>>> with the dma_alloc_coherent changes, the default value of CMA_AREAS >>>> was bumped up to 19 if NUMA is enabled. >>>> >>>> It seems that the number of CMA users is likely to grow. Instead of >>>> using a static array for cma areas, use a simple linked list. These >>>> areas are used before normal memory allocators, so use the memblock >>>> allocator. >>>> >>>> Acked-by: Roman Gushchin <guro@xxxxxx> >>>> Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx> >>>> --- >>>> rfc->v1 >>>> - Made minor changes suggested by Song Bao Hua (Barry Song) >>>> - Removed check for late calls to cma_init_reserved_mem that was part >>>> of RFC. >>>> - Added ACK from Roman Gushchin >>>> - Still in need of arm testing >>> >>> Unfortunately, the test result on my arm64 board is negative, Linux can't boot >>> after applying >>> this patch. >>> >>> I guess we have to hold on this patch for a while till this is fixed. BTW, Mike, do >>> you have >>> a qemu-based arm64 numa system to debug? It is very easy to reproduce, we >>> don't need to >>> use hugetlb_cma and pernuma_cma. Just the default cma will make the boot >>> hang. >> >> Hi Mike, >> I spent some time on debugging the boot issue and sent a patch here: >> https://lore.kernel.org/linux-mm/20200916085933.25220-1-song.bao.hua@xxxxxxxxxxxxx/ >> All details and knic oops can be found there. >> pls feel free to merge my patch into your v2 if you want. And we probably need ack from >> arm maintainers. >> >> Also, +Will, >> >> Hi Will, the whole story is that Mike tried to remove the cma array with CONFIG_CMA_AREAS >> and moved to use memblock_alloc() to allocate cma area, so that the number of cma areas >> could be dynamic. It turns out it causes a kernel panic on arm64 during system boot as the >> returned address from memblock_alloc is invalid before paging_init() is done on arm64. >> > > Thank you! > > Based on your analysis, I am concerned that other architectures may also > have issues. > > Andrew, > I suggest we remove this patch from your tree. I will audit all architectures > which enable CMA and look for similar issues there. Will then merge Barry's > patch into a V2 with any other arch specific changes. FYI This was also bisected on kernelci.org[1] and it landed on this commit: c999bd436fe9 ("mm/cma: make number of CMA areas dynamic, remove CONFIG_CMA_AREAS"). Only arm and arm64 seem to be affected, and not with all the builds: https://kernelci.org/test/job/next/branch/master/kernel/next-20200916/plan/baseline/ The list of failures above might help someone debug the issue with a platform they have at hand. Guillaume [1] https://groups.io/g/kernelci-results-staging/message/2027
