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mm: fix ia64 crash when gcore reads gate area 

Debian's ia64 autobuilders have been seeing kernel freeze or reboot
when running the gdb testsuite (Debian bug 588574): dannf bisected to
2.6.32 62eede62da "mm: ZERO_PAGE without
PTE_SPECIAL"; and reproduced it with gdb's gcore on a simple target.

I'd missed updating the gate_vma handling in __get_user_pages(): that
happens to use vm_normal_page() (nowadays failing on the zero page),
yet reported success even when it failed to get a page - boom when
access_process_vm() tried to copy that to its intermediate buffer.

Fix this, resisting cleanups: in particular, leave it for now reporting
success when not asked to get any pages - very probably safe to change,
but let's not risk it without testing exposure.

Why did ia64 crash with 16kB pages, but succeed with 64kB pages?
Because setup_gate() pads each 64kB of its gate area with zero pages.

Reported-by: Andreas Barth <aba@not.so.argh.org>
Bisected-by: dann frazier <dannf@debian.org>
Signed-off-by: Hugh Dickins <hughd@google.com>
Tested-by: dann frazier <dannf@dannf.org>
Cc: stable@kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
hifive-unleashed-5.1
Hugh Dickins 2010-07-30 10:58:26 -07:00 committed by Linus Torvalds
parent 51c20fcced
commit de51257aa3
1 changed files with 13 additions and 3 deletions
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16
mm/memory.c
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@ -1394,10 +1394,20 @@ int __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
return i ? : -EFAULT;
}
if (pages) {
struct page *page = vm_normal_page(gate_vma, start, *pte);
struct page *page;
page = vm_normal_page(gate_vma, start, *pte);
if (!page) {
if (!(gup_flags & FOLL_DUMP) &&
is_zero_pfn(pte_pfn(*pte)))
page = pte_page(*pte);
else {
pte_unmap(pte);
return i ? : -EFAULT;
}
}
pages[i] = page;
if (page)
get_page(page);
get_page(page);
}
pte_unmap(pte);
if (vmas)