Re: [PATCH] slab: Fix off by one in object max number tests.

[David Miller <davem@davemloft.net>]

From: Sam Ravnborg <sam@ravnborg.org>
Date: Mon, 5 May 2014 23:05:07 +0200

> On Mon, May 05, 2014 at 04:57:56PM -0400, David Miller wrote:
>> From: David Miller <davem@davemloft.net>
>> Date: Mon, 05 May 2014 16:20:04 -0400 (EDT)
>> 
>> > 
>> > If freelist_idx_t is a byte, SLAB_OBJ_MAX_NUM should be 255 not 256,
>> > and likewise if freelist_idx_t is a short, then it should be 65535 not
>> > 65536.
>> > 
>> > Fixes: a41adfa ("slab: introduce byte sized index for the freelist of a slab")
>> > Signed-off-by: David S. Miller <davem@davemloft.net>
>> > ---
>> > 
>> > This was leading to all kinds of random crashes on sparc64 where PAGE_SIZE
>> > is 8192.  One problem shown was that if spinlock debugging was enabled,
>> > we'd get deadlocks in copy_pte_range() or do_wp_page() with the same cpu
>> > already holding a lock it shouldn't hold, or the lock belonging to a
>> > completely unrelated process.
>> 
>> It turns out that after some more testing, I'm still getting spinlock
>> debugging problems with this fix applied.
>> 
>> The change is still very much correct I think, however.
> 
> There is a related patch in this area which I think is not yet applied.
> 
> See: https://lkml.org/lkml/2014/4/18/28
> 
> Maybe this is realted.

Thanks, I'm testing with that patch added as well.