From: Jerome Marchand <jmarchan@redhat.com>
To: Pekka Enberg <penberg@kernel.org>
Cc: Minchan Kim <minchan@kernel.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
Dan Magenheimer <dan.magenheimer@oracle.com>,
Nitin Gupta <ngupta@vflare.org>,
Konrad Rzeszutek Wilk <konrad@darnok.org>,
Seth Jennings <sjenning@linux.vnet.ibm.com>,
stable@vger.kernel.org
Subject: Re: [RESEND PATCH v5 1/4] zram: Fix deadlock bug in partial write
Date: Mon, 28 Jan 2013 14:47:01 +0100 [thread overview]
Message-ID: <51068155.4020807@redhat.com> (raw)
In-Reply-To: <CAOJsxLG=3sWdFkvb++f2ywhs288ozoMXZd_g2WOAgxTqxayY_Q@mail.gmail.com>
On 01/28/2013 02:26 PM, Pekka Enberg wrote:
> On Mon, Jan 28, 2013 at 1:24 PM, Jerome Marchand <jmarchan@redhat.com> wrote:
>> On 01/28/2013 08:16 AM, Pekka Enberg wrote:
>>> On Mon, Jan 28, 2013 at 2:38 AM, Minchan Kim <minchan@kernel.org> wrote:
>>>> Now zram allocates new page with GFP_KERNEL in zram I/O path
>>>> if IO is partial. Unfortunately, It may cuase deadlock with
>>>
>>> s/cuase/cause/g
>>>
>>>> reclaim path so this patch solves the problem.
>>>
>>> It'd be nice to know about the problem in more detail. I'm also
>>> curious on why you decided on GFP_ATOMIC for the read path and
>>> GFP_NOIO in the write path.
>>
>> This is because we're holding a kmap_atomic page in the read path.
>
> Okay, so that's about partial *reads* and not even mentioned in the
> changelog, no?
>
> AFAICT, you could rearrange the code in zram_bvec_read() as follows:
>
> if (is_partial_io(bvec))
> /* Use a temporary buffer to decompress the page */
> uncmem = kmalloc(PAGE_SIZE, GFP_KERNEL);
> else {
> uncmem = user_mem = kmap_atomic(page);
> }
>
> and avoid the GFP_ATOMIC allocation.
>
user_mem still has to be mapped in case of partial I/O too. But the
temporary buffer allocation could happen before. The allocation still
would need to be GFP_NOIO to avoid possible deadlocks.
Anyhow, the commit message could definitely be more explicit.
Regards,
Jerome
next prev parent reply other threads:[~2013-01-28 13:47 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-01-28 0:38 [RESEND PATCH v5 1/4] zram: Fix deadlock bug in partial write Minchan Kim
2013-01-28 0:38 ` [RESEND PATCH v5 2/4] zram: force disksize setting before using zram Minchan Kim
2013-01-28 0:38 ` [RESEND PATCH v5 3/4] zram: give up lazy initialization of zram metadata Minchan Kim
2013-01-28 0:38 ` [RESEND PATCH v5 4/4] zram: get rid of lockdep warning Minchan Kim
2013-01-28 7:16 ` [RESEND PATCH v5 1/4] zram: Fix deadlock bug in partial write Pekka Enberg
2013-01-28 11:24 ` Jerome Marchand
2013-01-28 13:26 ` Pekka Enberg
2013-01-28 13:47 ` Jerome Marchand [this message]
2013-01-28 23:21 ` Minchan Kim
2013-01-29 7:11 ` Pekka Enberg
2013-01-30 1:32 ` Minchan Kim
2013-01-30 4:20 ` Greg Kroah-Hartman
2013-01-30 8:21 ` Minchan Kim
2013-01-31 5:41 ` Minchan Kim
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