Messages in this thread | | | From | Nick Piggin <> | Subject | Re: [PATCH] [5/5] Avoid theoretical vmalloc fault loop | Date | Mon, 5 Jan 2009 22:47:56 +1100 |
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This should be a -stable patch too I think.
On Monday 05 January 2009 10:36:42 Andi Kleen wrote: > Ajith Kumar noticed: > > I was going through the vmalloc fault handling for x86_64 and am unclear > about the following lines in the vmalloc_fault() function. > > pgd = pgd_offset(current->mm ?: &init_mm, address); > pgd_ref = pgd_offset_k(address); > > Here the intention is to get the pgd corresponding to the current > process and sync it up with the pgd in init_mm(obtained from > pgd_offset_k). However, for kernel threads current->mm is NULL and hence > pgd = pgd_offset(init_mm, address) = pgd_ref which means the fault > handler returns without setting the pgd entry in the MM structure in > the context of which the kernel thread has faulted. This could lead to > never-ending faults and busy looping of kernel threads like pdflush. > So, shouldn't the pgd = pgd_offset(current->mm ?: &init_mm, address); > be > pgd = pgd_offset(current->active_mm ?: &init_mm, address); > > AK: We can use active_mm unconditionally because it should > be always set. Do that. > > Signed-off-by: Andi Kleen <ak@linux.intel.com> > > --- > arch/x86/mm/fault.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > Index: linux-2.6.28-test/arch/x86/mm/fault.c > =================================================================== > --- linux-2.6.28-test.orig/arch/x86/mm/fault.c 2008-10-24 > 13:34:41.000000000 +0200 +++ > linux-2.6.28-test/arch/x86/mm/fault.c 2009-01-02 16:01:11.000000000 +0100 > @@ -533,7 +533,7 @@ > happen within a race in page table update. In the later > case just flush. */ > > - pgd = pgd_offset(current->mm ?: &init_mm, address); > + pgd = pgd_offset(current->active_mm, address); > pgd_ref = pgd_offset_k(address); > if (pgd_none(*pgd_ref)) > return -1; > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/
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