• Andi Kleen's avatar
    x86: avoid theoretical vmalloc fault loop · f313e123
    Andi Kleen authored
    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: default avatarAndi Kleen <ak@linux.intel.com>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
fault.c 22.9 KB