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futexes: Fix infinite loop in get_futex_key() on huge page

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get_futex_key() can infinitely loop if it is called on a
virtual address that is within a huge page but not aligned to
the beginning of that page.  The call to get_user_pages_fast
will return the struct page for a sub-page within the huge page
and the check for page->mapping will always fail.

The fix is to call compound_head on the page before checking
that it's mapped.

Signed-off-by: Sonny Rao <sonnyrao@us.ibm.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@kernel.org
Cc: anton@samba.org
Cc: rajamony@us.ibm.com
Cc: speight@us.ibm.com
Cc: mstephen@us.ibm.com
Cc: grimm@us.ibm.com
Cc: mikey@ozlabs.au.ibm.com
LKML-Reference: <20090710231313.GA23572@us.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Sonny Rao 2009-07-10 18:13:13 -05:00 committed by Ingo Molnar
parent f00caa7629
commit ce2ae53b75
1 changed files with 1 additions and 0 deletions
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kernel/futex.c
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@ -247,6 +247,7 @@ again:
if (err < 0)
return err;
page = compound_head(page);
lock_page(page);
if (!page->mapping) {
unlock_page(page);