3.19-stable review patch. If anyone has any objections, please let me know. ------------------ From: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx> commit 05fbf357d94152171bc50f8a369390f1f16efd89 upstream. Lockless access to pte in pagemap_pte_range() might race with page migration and trigger BUG_ON(!PageLocked()) in migration_entry_to_page(): CPU A (pagemap) CPU B (migration) lock_page() try_to_unmap(page, TTU_MIGRATION...) make_migration_entry() set_pte_at() <read *pte> pte_to_pagemap_entry() remove_migration_ptes() unlock_page() if(is_migration_entry()) migration_entry_to_page() BUG_ON(!PageLocked(page)) Also lockless read might be non-atomic if pte is larger than wordsize. Other pte walkers (smaps, numa_maps, clear_refs) already lock ptes. Fixes: 052fb0d635df ("proc: report file/anon bit in /proc/pid/pagemap") Signed-off-by: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx> Reported-by: Andrey Ryabinin <a.ryabinin@xxxxxxxxxxx> Reviewed-by: Cyrill Gorcunov <gorcunov@xxxxxxxxxx> Acked-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx> Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- fs/proc/task_mmu.c | 14 +++++++++----- 1 file changed, 9 insertions(+), 5 deletions(-) --- a/fs/proc/task_mmu.c +++ b/fs/proc/task_mmu.c @@ -1069,7 +1069,7 @@ static int pagemap_pte_range(pmd_t *pmd, struct vm_area_struct *vma; struct pagemapread *pm = walk->private; spinlock_t *ptl; - pte_t *pte; + pte_t *pte, *orig_pte; int err = 0; /* find the first VMA at or above 'addr' */ @@ -1130,15 +1130,19 @@ static int pagemap_pte_range(pmd_t *pmd, BUG_ON(is_vm_hugetlb_page(vma)); /* Addresses in the VMA. */ - for (; addr < min(end, vma->vm_end); addr += PAGE_SIZE) { + orig_pte = pte = pte_offset_map_lock(walk->mm, pmd, addr, &ptl); + for (; addr < min(end, vma->vm_end); pte++, addr += PAGE_SIZE) { pagemap_entry_t pme; - pte = pte_offset_map(pmd, addr); + pte_to_pagemap_entry(&pme, pm, vma, addr, *pte); - pte_unmap(pte); err = add_to_pagemap(addr, &pme, pm); if (err) - return err; + break; } + pte_unmap_unlock(orig_pte, ptl); + + if (err) + return err; if (addr == end) break; -- 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