From 891121e6c02c6242487aa4ea1d5c75b7ecdc45ee Mon Sep 17 00:00:00 2001 From: "Aneesh Kumar K.V" Date: Fri, 9 Oct 2015 08:32:21 +0530 Subject: powerpc/mm: Differentiate between hugetlb and THP during page walk We need to properly identify whether a hugepage is an explicit or a transparent hugepage in follow_huge_addr(). We used to depend on hugepage shift argument to do that. But in some case that can result in wrong results. For ex: On finding a transparent hugepage we set hugepage shift to PMD_SHIFT. But we can end up clearing the thp pte, via pmdp_huge_get_and_clear. We do prevent reusing the pfn page via the usage of kick_all_cpus_sync(). But that happens after we updated the pte to 0. Hence in follow_huge_addr() we can find hugepage shift set, but transparent huge page check fail for a thp pte. NOTE: We fixed a variant of this race against thp split in commit 691e95fd7396905a38d98919e9c150dbc3ea21a3 ("powerpc/mm/thp: Make page table walk safe against thp split/collapse") Without this patch, we may hit the BUG_ON(flags & FOLL_GET) in follow_page_mask occasionally. In the long term, we may want to switch ppc64 64k page size config to enable CONFIG_ARCH_WANT_GENERAL_HUGETLB Reported-by: David Gibson Signed-off-by: Aneesh Kumar K.V Signed-off-by: Michael Ellerman --- arch/powerpc/perf/callchain.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'arch/powerpc/perf/callchain.c') diff --git a/arch/powerpc/perf/callchain.c b/arch/powerpc/perf/callchain.c index ff09cde20cd2..e04a6752b399 100644 --- a/arch/powerpc/perf/callchain.c +++ b/arch/powerpc/perf/callchain.c @@ -127,7 +127,7 @@ static int read_user_stack_slow(void __user *ptr, void *buf, int nb) return -EFAULT; local_irq_save(flags); - ptep = find_linux_pte_or_hugepte(pgdir, addr, &shift); + ptep = find_linux_pte_or_hugepte(pgdir, addr, NULL, &shift); if (!ptep) goto err_out; if (!shift) -- cgit