From: Andi Kleen Date: Fri, 9 Jan 2009 20:17:43 +0000 (-0800) Subject: x86: avoid theoretical vmalloc fault loop X-Git-Tag: 2.1b_release~13986^2~70 X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=f313e12308f7c5ea645f18e759d104d088b18615;p=platform%2Fkernel%2Fkernel-mfld-blackbay.git x86: avoid theoretical vmalloc fault loop 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); We can use active_mm unconditionally because it should be always set. Signed-off-by: Andi Kleen Signed-off-by: Andrew Morton Signed-off-by: Ingo Molnar --- diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c index 9e268b6b..90dfae5 100644 --- a/arch/x86/mm/fault.c +++ b/arch/x86/mm/fault.c @@ -534,7 +534,7 @@ static int vmalloc_fault(unsigned long address) 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;