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Fix 'get_user_pages_fast()' with non-page-aligned start address 

Alexey Dobriyan reported trouble with LTP with the new fast-gup code,
and Johannes Weiner debugged it to non-page-aligned addresses, where the
new get_user_pages_fast() code would do all the wrong things, including
just traversing past the end of the requested area due to 'addr' never
matching 'end' exactly.

This is not a pretty fix, and we may actually want to move the alignment
into generic code, leaving just the core code per-arch, but Alexey
verified that the vmsplice01 LTP test doesn't crash with this.

Reported-and-tested-by: Alexey Dobriyan <adobriyan@gmail.com>
Debugged-by: Johannes Weiner <hannes@saeurebad.de>
Cc: Nick Piggin <npiggin@suse.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Linus Torvalds 2008-07-28 17:54:21 -07:00
parent 34ee550142
commit 9b79022ca9
1 changed files with 6 additions and 3 deletions
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9
arch/x86/mm/gup.c
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@ -223,14 +223,17 @@ int get_user_pages_fast(unsigned long start, int nr_pages, int write,
struct page **pages)
{
struct mm_struct *mm = current->mm;
unsigned long end = start + (nr_pages << PAGE_SHIFT);
unsigned long addr = start;
unsigned long addr, len, end;
unsigned long next;
pgd_t *pgdp;
int nr = 0;
start &= PAGE_MASK;
addr = start;
len = (unsigned long) nr_pages << PAGE_SHIFT;
end = start + len;
if (unlikely(!access_ok(write ? VERIFY_WRITE : VERIFY_READ,
start, nr_pages*PAGE_SIZE)))
start, len)))
goto slow_irqon;
/*