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Commit 16abfa08 authored by Hugh Dickins's avatar Hugh Dickins Committed by Linus Torvalds
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Fix sys_remap_file_pages BUG at highmem.c:15! 



Gurudas Pai reports kernel BUG at arch/i386/mm/highmem.c:15! below
sys_remap_file_pages, while running Oracle database test on x86 in 6GB
RAM: kunmap thinks we're in_interrupt because the preempt count has
wrapped.

That's because __do_fault expected to unmap page_table, but one of its
two callers do_nonlinear_fault already unmapped it: let do_linear_fault
unmap it first too, and then there's no need to pass the page_table arg
down.

Why have we been so slow to notice this? Probably through forgetting
that the mapping_cap_account_dirty test means that sys_remap_file_pages
nowadays only goes the full nonlinear vma route on a few memory-backed
filesystems like ramfs, tmpfs and hugetlbfs.

[ It also depends on CONFIG_HIGHPTE, so it becomes even harder to
  trigger in practice. Many who have need of large memory have probably
  migrated to x86-64..

  Problem introduced by commit d0217ac0
  ("mm: fault feedback #1")                -- Linus ]

Signed-off-by: default avatarHugh Dickins <hugh@veritas.com>
Cc: gurudas pai <gurudas.pai@oracle.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 804b3f9a

mm/memory.c

+6 −8
Original line number Diff line number Diff line
@@ -2307,13 +2307,14 @@ static int do_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma, 
 * do not need to flush old virtual caches or the TLB.

 *

 * We enter with non-exclusive mmap_sem (to exclude vma changes,

 * but allow concurrent faults), and pte mapped but not yet locked.

 * but allow concurrent faults), and pte neither mapped nor locked.

 * We return with mmap_sem still held, but pte unmapped and unlocked.

 */

static int __do_fault(struct mm_struct *mm, struct vm_area_struct *vma,

		unsigned long address, pte_t *page_table, pmd_t *pmd,

		unsigned long address, pmd_t *pmd,

		pgoff_t pgoff, unsigned int flags, pte_t orig_pte)

{

	pte_t *page_table;

	spinlock_t *ptl;

	struct page *page;

	pte_t entry;
@@ -2327,7 +2328,6 @@ static int __do_fault(struct mm_struct *mm, struct vm_area_struct *vma, 
	vmf.flags = flags;

	vmf.page = NULL;



	pte_unmap(page_table);

	BUG_ON(vma->vm_flags & VM_PFNMAP);



	if (likely(vma->vm_ops->fault)) {
@@ -2468,8 +2468,8 @@ static int do_linear_fault(struct mm_struct *mm, struct vm_area_struct *vma, 
			- vma->vm_start) >> PAGE_CACHE_SHIFT) + vma->vm_pgoff;

	unsigned int flags = (write_access ? FAULT_FLAG_WRITE : 0);



	return __do_fault(mm, vma, address, page_table, pmd, pgoff,

							flags, orig_pte);

	pte_unmap(page_table);

	return __do_fault(mm, vma, address, pmd, pgoff, flags, orig_pte);

}
@@ -2552,9 +2552,7 @@ static int do_nonlinear_fault(struct mm_struct *mm, struct vm_area_struct *vma, 
	}



	pgoff = pte_to_pgoff(orig_pte);



	return __do_fault(mm, vma, address, page_table, pmd, pgoff,

							flags, orig_pte);

	return __do_fault(mm, vma, address, pmd, pgoff, flags, orig_pte);

}



/*