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mm: fix swapops.h:131 bug if remap_file_pages raced migration

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Add remove_linear_migration_ptes_from_nonlinear(), to fix an interesting
little include/linux/swapops.h:131 BUG_ON(!PageLocked) found by trinity:
indicating that remove_migration_ptes() failed to find one of the
migration entries that was temporarily inserted.

The problem comes from remap_file_pages()'s switch from vma_interval_tree
(good for inserting the migration entry) to i_mmap_nonlinear list (no good
for locating it again); but can only be a problem if the remap_file_pages()
range does not cover the whole of the vma (zap_pte() clears the range).

remove_migration_ptes() needs a file_nonlinear method to go down the
i_mmap_nonlinear list, applying linear location to look for migration
entries in those vmas too, just in case there was this race.

The file_nonlinear method does need rmap_walk_control.arg to do this;
but it never needed vma passed in - vma comes from its own iteration.

Reported-and-tested-by: Dave Jones <davej@redhat.com>
Reported-and-tested-by: Sasha Levin <sasha.levin@oracle.com>
Signed-off-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Hugh Dickins 2014-03-20 21:52:17 -07:00 committed by Linus Torvalds
parent 3fb725c48b
commit 7e09e738af
3 changed files with 36 additions and 4 deletions
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3
include/linux/rmap.h
View file

@ -250,8 +250,7 @@ struct rmap_walk_control {
int (*rmap_one)(struct page *page, struct vm_area_struct *vma,
unsigned long addr, void *arg);
int (*done)(struct page *page);
int (*file_nonlinear)(struct page *, struct address_space *,
struct vm_area_struct *vma);
int (*file_nonlinear)(struct page *, struct address_space *, void *arg);
struct anon_vma *(*anon_lock)(struct page *page);
bool (*invalid_vma)(struct vm_area_struct *vma, void *arg);
};

32
mm/migrate.c
View file

@ -177,6 +177,37 @@ static int remove_migration_pte(struct page *new, struct vm_area_struct *vma,
return SWAP_AGAIN;
}
/*
* Congratulations to trinity for discovering this bug.
* mm/fremap.c's remap_file_pages() accepts any range within a single vma to
* convert that vma to VM_NONLINEAR; and generic_file_remap_pages() will then
* replace the specified range by file ptes throughout (maybe populated after).
* If page migration finds a page within that range, while it's still located
* by vma_interval_tree rather than lost to i_mmap_nonlinear list, no problem:
* zap_pte() clears the temporary migration entry before mmap_sem is dropped.
* But if the migrating page is in a part of the vma outside the range to be
* remapped, then it will not be cleared, and remove_migration_ptes() needs to
* deal with it. Fortunately, this part of the vma is of course still linear,
* so we just need to use linear location on the nonlinear list.
*/
static int remove_linear_migration_ptes_from_nonlinear(struct page *page,
struct address_space *mapping, void *arg)
{
struct vm_area_struct *vma;
/* hugetlbfs does not support remap_pages, so no huge pgoff worries */
pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
unsigned long addr;
list_for_each_entry(vma,
&mapping->i_mmap_nonlinear, shared.nonlinear) {
addr = vma->vm_start + ((pgoff - vma->vm_pgoff) << PAGE_SHIFT);
if (addr >= vma->vm_start && addr < vma->vm_end)
remove_migration_pte(page, vma, addr, arg);
}
return SWAP_AGAIN;
}
/*
* Get rid of all migration entries and replace them by
* references to the indicated page.
@ -186,6 +217,7 @@ static void remove_migration_ptes(struct page *old, struct page *new)
struct rmap_walk_control rwc = {
.rmap_one = remove_migration_pte,
.arg = old,
.file_nonlinear = remove_linear_migration_ptes_from_nonlinear,
};
rmap_walk(new, &rwc);

5
mm/rmap.c
View file

@ -1360,8 +1360,9 @@ static int try_to_unmap_cluster(unsigned long cursor, unsigned int *mapcount,
}
static int try_to_unmap_nonlinear(struct page *page,
struct address_space *mapping, struct vm_area_struct *vma)
struct address_space *mapping, void *arg)
{
struct vm_area_struct *vma;
int ret = SWAP_AGAIN;
unsigned long cursor;
unsigned long max_nl_cursor = 0;
@ -1663,7 +1664,7 @@ static int rmap_walk_file(struct page *page, struct rmap_walk_control *rwc)
if (list_empty(&mapping->i_mmap_nonlinear))
goto done;
ret = rwc->file_nonlinear(page, mapping, vma);
ret = rwc->file_nonlinear(page, mapping, rwc->arg);
done:
mutex_unlock(&mapping->i_mmap_mutex);