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mm/munlock: mlock_vma_page() check against VM_SPECIAL

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Although mmap_region() and mlock_fixup() take care that VM_LOCKED
is never left set on a VM_SPECIAL vma, there is an interval while
file->f_op->mmap() is using vm_insert_page(s), when VM_LOCKED may
still be set while VM_SPECIAL bits are added: so mlock_vma_page()
should ignore VM_LOCKED while any VM_SPECIAL bits are set.

This showed up as a "Bad page" still mlocked, when vfree()ing pages
which had been vm_inserted by remap_vmalloc_range_partial(): while
release_pages() and __page_cache_release(), and so put_page(), catch
pages still mlocked when freeing (and clear_page_mlock() caught them
when unmapping), the vfree() path is unprepared for them: fix it?
but these pages should not have been mlocked in the first place.

I assume that an mlockall(MCL_FUTURE) had been done in the past; or
maybe the user got to specify MAP_LOCKED on a vmalloc'ing driver mmap.

Signed-off-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
This commit is contained in:
Hugh Dickins 2022-03-02 17:35:30 -08:00 committed by Matthew Wilcox (Oracle)
parent 47d4f3eeef
commit c8263bd605
1 changed files with 9 additions and 2 deletions
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11
mm/internal.h
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@ -413,8 +413,15 @@ void mlock_page(struct page *page);
static inline void mlock_vma_page(struct page *page,
struct vm_area_struct *vma, bool compound)
{
/* VM_IO check prevents migration from double-counting during mlock */
if (unlikely((vma->vm_flags & (VM_LOCKED|VM_IO)) == VM_LOCKED) &&
/*
* The VM_SPECIAL check here serves two purposes.
* 1) VM_IO check prevents migration from double-counting during mlock.
* 2) Although mmap_region() and mlock_fixup() take care that VM_LOCKED
* is never left set on a VM_SPECIAL vma, there is an interval while
* file->f_op->mmap() is using vm_insert_page(s), when VM_LOCKED may
* still be set while VM_SPECIAL bits are added: so ignore it then.
*/
if (unlikely((vma->vm_flags & (VM_LOCKED|VM_SPECIAL)) == VM_LOCKED) &&
(compound || !PageTransCompound(page)))
mlock_page(page);
}