From: Minchan Kim <minchan@xxxxxxxxxx> Subject: mm: pmd dirty emulation in page fault handler Andreas reported [1] made a test in jemalloc hang in THP mode in arm64. http://lkml.kernel.org/r/mvmmvfy37g1.fsf@xxxxxxxxxxxxxxx The problem is currently page fault handler doesn't supports dirty bit emulation of pmd for non-HW dirty-bit architecture so that application stucks until VM marked the pmd dirty. How the emulation work depends on the architecture. In case of arm64, when it set up pte firstly, it sets pte PTE_RDONLY to get a chance to mark the pte dirty via triggering page fault when store access happens. Once the page fault occurs, VM marks the pmd dirty and arch code for setting pmd will clear PTE_RDONLY for application to proceed. IOW, if VM doesn't mark the pmd dirty, application hangs forever by repeated fault(i.e., store op but the pmd is PTE_RDONLY). This patch enables pmd dirty-bit emulation for those architectures. [1] b8d3c4c3009d, mm/huge_memory.c: don't split THP page when MADV_FREE syscall is called Fixes: b8d3c4c3009d ("mm/huge_memory.c: don't split THP page when MADV_FREE syscall is called") Link: http://lkml.kernel.org/r/1482506098-6149-1-git-send-email-minchan@xxxxxxxxxx Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx> Reported-by: Andreas Schwab <schwab@xxxxxxx> Tested-by: Andreas Schwab <schwab@xxxxxxx> Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> Acked-by: Michal Hocko <mhocko@xxxxxxxx> Cc: Jason Evans <je@xxxxxx> Cc: Will Deacon <will.deacon@xxxxxxx> Cc: Catalin Marinas <catalin.marinas@xxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> [4.5+] Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/huge_memory.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff -puN mm/huge_memory.c~mm-pmd-dirty-emulation-in-page-fault-handler mm/huge_memory.c --- a/mm/huge_memory.c~mm-pmd-dirty-emulation-in-page-fault-handler +++ a/mm/huge_memory.c @@ -883,15 +883,17 @@ void huge_pmd_set_accessed(struct vm_fau { pmd_t entry; unsigned long haddr; + bool write = vmf->flags & FAULT_FLAG_WRITE; vmf->ptl = pmd_lock(vmf->vma->vm_mm, vmf->pmd); if (unlikely(!pmd_same(*vmf->pmd, orig_pmd))) goto unlock; entry = pmd_mkyoung(orig_pmd); + if (write) + entry = pmd_mkdirty(entry); haddr = vmf->address & HPAGE_PMD_MASK; - if (pmdp_set_access_flags(vmf->vma, haddr, vmf->pmd, entry, - vmf->flags & FAULT_FLAG_WRITE)) + if (pmdp_set_access_flags(vmf->vma, haddr, vmf->pmd, entry, write)) update_mmu_cache_pmd(vmf->vma, vmf->address, vmf->pmd); unlock: _ -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html