From: "Peng Wang" <rocking@whu.edu.cn>
To: 'Matthew Wilcox' <willy@infradead.org>
Cc: cl@linux.com, penberg@kernel.org, rientjes@google.com,
iamjoonsoo.kim@lge.com, akpm@linux-foundation.org,
linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: RE: [PATCH] mm/slub.c: re-randomize random_seq if necessary
Date: Wed, 9 Jan 2019 23:24:44 +0800 [thread overview]
Message-ID: <000501d4a82f$74821b40$5d8651c0$@whu.edu.cn> (raw)
In-Reply-To: <20190109121352.GI6310@bombadil.infradead.org>
On Wednesday, January 9, 2019 8:14 PM, Matthew Wilcox wrote:
> On Wed, Jan 09, 2019 at 05:06:27PM +0800, Peng Wang wrote:
> > calculate_sizes() could be called in several places
> > like (red_zone/poison/order/store_user)_store() while
> > random_seq remains unchanged.
> >
> > If random_seq is not NULL in calculate_sizes(), re-randomize it.
>
> Why do we want to re-randomise the slab at these points?
At these points, s->size might change,
but random_seq still use the old size and not updated.
When doing shuffle_freelist() in allocat_slab(),
old next object offset would be used.
idx = s->random_seq[*pos];
One possible case:
s->size gets smaller, then number of objects in a slab gets bigger.
The size of s->random_seq array should be bigger but not updated.
In next_freelist_entry(), *pos might exceed the s->random_seq.
When we get zero value from s->random_seq[*pos] twice after exceeding,
BUG_ON(object == fp) would be triggered in set_freepointer().
WARNING: multiple messages have this Message-ID
From: "Peng Wang" <rocking@whu.edu.cn>
To: "'Matthew Wilcox'" <willy@infradead.org>
Cc: <cl@linux.com>, <penberg@kernel.org>, <rientjes@google.com>,
<iamjoonsoo.kim@lge.com>, <akpm@linux-foundation.org>,
<linux-mm@kvack.org>, <linux-kernel@vger.kernel.org>
Subject: RE: [PATCH] mm/slub.c: re-randomize random_seq if necessary
Date: Wed, 9 Jan 2019 23:24:44 +0800 [thread overview]
Message-ID: <000501d4a82f$74821b40$5d8651c0$@whu.edu.cn> (raw)
Message-ID: <20190109152444.RLNtgft24Zf4QvzLP7eYXdIUXuYx8Cv5epW8Xm3tOQ0@z> (raw)
In-Reply-To: <20190109121352.GI6310@bombadil.infradead.org>
On Wednesday, January 9, 2019 8:14 PM, Matthew Wilcox wrote:
> On Wed, Jan 09, 2019 at 05:06:27PM +0800, Peng Wang wrote:
> > calculate_sizes() could be called in several places
> > like (red_zone/poison/order/store_user)_store() while
> > random_seq remains unchanged.
> >
> > If random_seq is not NULL in calculate_sizes(), re-randomize it.
>
> Why do we want to re-randomise the slab at these points?
At these points, s->size might change,
but random_seq still use the old size and not updated.
When doing shuffle_freelist() in allocat_slab(),
old next object offset would be used.
idx = s->random_seq[*pos];
One possible case:
s->size gets smaller, then number of objects in a slab gets bigger.
The size of s->random_seq array should be bigger but not updated.
In next_freelist_entry(), *pos might exceed the s->random_seq.
When we get zero value from s->random_seq[*pos] twice after exceeding,
BUG_ON(object == fp) would be triggered in set_freepointer().
next prev parent reply other threads:[~2019-01-09 15:24 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-09 9:06 Peng Wang
2019-01-09 12:13 ` Matthew Wilcox
2019-01-09 15:24 ` Peng Wang [this message]
2019-01-09 15:24 ` Peng Wang
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