From 2f9297bc01dc95cc1ab93d3c1b353a04edd49135 Mon Sep 17 00:00:00 2001 From: Andi Kleen Date: Fri, 9 Jan 2009 12:17:43 -0800 Subject: [PATCH] x86: avoid theoretical vmalloc fault loop commit f313e12308f7c5ea645f18e759d104d088b18615 upstream. 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 Signed-off-by: Greg Kroah-Hartman --- arch/x86/mm/fault.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c index 455f3fe67b42..da1973b9a6e2 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; -- 2.39.2