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authorAneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>2015-10-09 08:32:21 +0530
committerMichael Ellerman <mpe@ellerman.id.au>2015-10-12 15:30:09 +1100
commit891121e6c02c6242487aa4ea1d5c75b7ecdc45ee (patch)
tree118c5b4df68fe004438e4a1a629b04fbeed9b417 /arch/powerpc/kernel/io-workarounds.c
parentec2640b114d535ba7d895b6ee353791d542f2407 (diff)
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 <david@gibson.dropbear.id.au> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Diffstat (limited to 'arch/powerpc/kernel/io-workarounds.c')
-rw-r--r--arch/powerpc/kernel/io-workarounds.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/arch/powerpc/kernel/io-workarounds.c b/arch/powerpc/kernel/io-workarounds.c
index 63d9cc4d7366..5f8613ceb97f 100644
--- a/arch/powerpc/kernel/io-workarounds.c
+++ b/arch/powerpc/kernel/io-workarounds.c
@@ -76,7 +76,7 @@ struct iowa_bus *iowa_mem_find_bus(const PCI_IO_ADDR addr)
* a page table free due to init_mm
*/
ptep = __find_linux_pte_or_hugepte(init_mm.pgd, vaddr,
- &hugepage_shift);
+ NULL, &hugepage_shift);
if (ptep == NULL)
paddr = 0;
else {