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ARM: Initialize ptl->lock for vector page 

Without this patch, ARM can not use SPLIT_PTLOCK_CPUS if
PREEMPT_RT_FULL=y because vectors_user_mapping() creates a
VM_ALWAYSDUMP mapping of the vector page (address 0xffff0000), but no
ptl->lock has been allocated for the page.  An attempt to coredump
that page will result in a kernel NULL pointer dereference when
follow_page() attempts to lock the page.

The call tree to the NULL pointer dereference is:

   do_notify_resume()
      get_signal_to_deliver()
         do_coredump()
            elf_core_dump()
               get_dump_page()
                  __get_user_pages()
                     follow_page()
                        pte_offset_map_lock() <----- a #define
                           ...
                              rt_spin_lock()

The underlying problem is exposed by mm-shrink-the-page-frame-to-rt-size.patch.

Signed-off-by: Frank Rowand <frank.rowand@am.sony.com>
Cc: Frank <Frank_Rowand@sonyusa.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/4E87C535.2030907@am.sony.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
Frank Rowand 2011-10-01 18:58:13 -07:00 committed by Alibek Omarov
parent 8972c413b1
commit 3026662099
1 changed files with 24 additions and 0 deletions
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24
arch/arm/kernel/process.c
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@ -434,6 +434,30 @@ unsigned long arch_randomize_brk(struct mm_struct *mm)
}
#ifdef CONFIG_MMU
/*
* CONFIG_SPLIT_PTLOCK_CPUS results in a page->ptl lock. If the lock is not
* initialized by pgtable_page_ctor() then a coredump of the vector page will
* fail.
*/
static int __init vectors_user_mapping_init_page(void)
{
struct page *page;
unsigned long addr = 0xffff0000;
pgd_t *pgd;
pud_t *pud;
pmd_t *pmd;
pgd = pgd_offset_k(addr);
pud = pud_offset(pgd, addr);
pmd = pmd_offset(pud, addr);
page = pmd_page(*(pmd));
pgtable_page_ctor(page);
return 0;
}
late_initcall(vectors_user_mapping_init_page);
#ifdef CONFIG_KUSER_HELPERS
/*
* The vectors page is always readable from user space for the