Commit 9b79022c authored Jul 28, 2008 by Linus Torvalds

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>

parent 34ee5501

arch/x86/mm/gup.c

+6 −3

Original line number	Original line	Diff line number	Diff line
	@@ -223,14 +223,17 @@ int get_user_pages_fast(unsigned long start, int nr_pages, int write,
	struct page **pages)		struct page **pages)
	{		{
	struct mm_struct *mm = current->mm;		struct mm_struct *mm = current->mm;
	unsigned long end = start + (nr_pages << PAGE_SHIFT);		unsigned long addr, len, end;
	unsigned long addr = start;
	unsigned long next;		unsigned long next;
	pgd_t *pgdp;		pgd_t *pgdp;
	int nr = 0;		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,		if (unlikely(!access_ok(write ? VERIFY_WRITE : VERIFY_READ,
	start, nr_pages*PAGE_SIZE)))		start, len)))
	goto slow_irqon;		goto slow_irqon;

	/*		/*

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