Re: odd memory corruption in 2.5.27?

[William Lee Irwin III <wli@holomorphy.com>]

On Tue, Jul 23, 2002 at 01:32:11PM -0700, george anzinger wrote:
> I just spent a month tracking down this issue.  It comes
> down to the slab allocater using per cpu data structures and
> protecting them with a combination of interrupt disables and
> spin_locks.  Preemption is allowed (incorrectly) if
> interrupts are off and preempt_count goes to zero on the
> spin_unlock.  I will wager that this is an SMP machine. 
> After the preemption interrupts will be on (schedule() does
> that) AND you could be on a different cpu.  Either of these
> is a BAD thing.
> The proposed fix is to catch the attempted preemption in
> preempt_schedule() and just return if the interrupt system
> is off.  (Of course there is more that this to it, but I do
> believe that the problem is known.  You could blow this
> assertion out of the water by asserting that the machine is
> NOT smp.)

I've been seeing the slab allocator race like mad already (i.e.
BUG at slab.c:1947 and slab.c:1961. I'll test this fix.


Thanks,
Bill