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

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Date:	Mon, 05 May 2014 16:57:56 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	linux-kernel@...r.kernel.org
Cc:	iamjoonsoo.kim@....com, sparclinux@...r.kernel.org,
	hannes@...xchg.org, cl@...ux.com, penberg@...nel.org,
	torvalds@...ux-foundation.org
Subject: Re: [PATCH] slab: Fix off by one in object max number tests.

From: David Miller <davem@...emloft.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@...emloft.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.
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