From: Ganesh Mahendran <opensource.ganesh@gmail.com>
To: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
Minchan Kim <minchan@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
linux-kernel <linux-kernel@vger.kernel.org>,
Linux-MM <linux-mm@kvack.org>, Nitin Gupta <ngupta@vflare.org>,
Jerome Marchand <jmarchan@redhat.com>
Subject: Re: [PATCH v1 2/2] zram: remove init_lock in zram_make_request
Date: Sat, 31 Jan 2015 20:59:31 +0800 [thread overview]
Message-ID: <CADAEsF_7vJrYf09s4DZ7AOvXrAwJeoCCZ0EKxwHeHHURBVQ6Bw@mail.gmail.com> (raw)
In-Reply-To: <20150131110743.GA2299@swordfish>
Hello, Sergey
2015-01-31 19:07 GMT+08:00 Sergey Senozhatsky <sergey.senozhatsky@gmail.com>:
> On (01/31/15 16:50), Ganesh Mahendran wrote:
>> >> > after umount we still have init device. so, *theoretically*, we
>> >> > can see something like
>> >> >
>> >> > CPU0 CPU1
>> >> > umount
>> >> > reset_store
>> >> > bdev->bd_holders == 0 mount
>> >> > ... zram_make_request()
>> >> > zram_reset_device()
> [..]
>
>
>>
>> Maybe I did not explain clearly. I send a patch about this issue:
>>
>> https://patchwork.kernel.org/patch/5754041/
>
>
> excuse me? explain to me clearly what? my finding and my analysis?
Sorry, I missed this mail
https://lkml.org/lkml/2015/1/27/1029
That's why I ask questions in this
https://lkml.org/lkml/2015/1/29/580
after Minchan's description.
>
>
> this is the second time in a week that you hijack someone's work
> and you don't even bother to give any credit to people.
>
>
> Minchan moved zram_meta_free(meta) out of init_lock here
> https://lkml.org/lkml/2015/1/21/29
>
> I proposed to also move zs_free() of meta->handles here
> https://lkml.org/lkml/2015/1/21/384
I thought you wanted move the code block after
up_write(&zram->init_lock);
And I found the code block can be even encapsulated in
zram_meta_free().
That's why I sent:
https://lkml.org/lkml/2015/1/24/50
>
>
> ... so what happened then -- you jumped in and sent a patch.
> https://lkml.org/lkml/2015/1/24/50
>
>
> Minchan sent you a hint https://lkml.org/lkml/2015/1/26/471
>
>> but it seems the patch is based on my recent work "zram: free meta out of init_lock".
>
>
>
> "the patch is based on my work"!
>
>
>
> now, for the last few days we were discussing init_lock and I first
> expressed my concerns and spoke about 'free' vs. 'use' problem
> here (but still didn't have enough spare to submit, besides we are in
> the middle of reset/init/write rework)
>
> https://lkml.org/lkml/2015/1/27/1029
>
>>
>>bdev->bd_holders protects from resetting device which has read/write
>>operation ongoing on the onther CPU.
>>
>>I need to refresh on how ->bd_holders actually incremented/decremented.
>>can the following race condition take a place?
>>
>> CPU0 CPU1
>>reset_store()
>>bdev->bd_holders == false
>> zram_make_request
>> -rm- down_read(&zram->init_lock);
>> init_done(zram) == true
>>zram_reset_device() valid_io_request()
>> __zram_make_request
>>down_write(&zram->init_lock); zram_bvec_rw
>>[..]
>>set_capacity(zram->disk, 0);
>>zram->init_done = false;
>>kick_all_cpus_sync(); zram_bvec_write or zram_bvec_read()
>>zram_meta_free(zram->meta);
>>zcomp_destroy(zram->comp); zcomp_compress() or zcomp_decompress()
Sorry, I did not check this mail.
>>
>
>
> and later here https://lkml.org/lkml/2015/1/29/645
>
>>
>>after umount we still have init device. so, *theoretically*, we
>>can see something like
>>
>>
>> CPU0 CPU1
>>umount
>>reset_store
>>bdev->bd_holders == 0 mount
>>... zram_make_request()
>>zram_reset_device()
>>
>
>
>
> so what happened next? your patch happened next.
> with quite familiar problem description
>
>>
>> CPU0 CPU1
>> t1: bdput
>> t2: mount /dev/zram0 /mnt
>> t3: zram_reset_device
>>
>
> and now you say that I don't understant something in "your analysis"?
>
>
>
> stop doing this. this is not how it works.
>
>
> -ss
>
next prev parent reply other threads:[~2015-01-31 12:59 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <1422432945-6764-1-git-send-email-minchan@kernel.org>
2015-01-28 14:19 ` [PATCH 1/2] zram: free meta table in zram_meta_free Sergey Senozhatsky
2015-01-28 23:17 ` Minchan Kim
2015-01-29 1:49 ` Ganesh Mahendran
[not found] ` <1422432945-6764-2-git-send-email-minchan@kernel.org>
2015-01-28 14:56 ` [PATCH v1 2/2] zram: remove init_lock in zram_make_request Sergey Senozhatsky
2015-01-28 15:04 ` Sergey Senozhatsky
2015-01-28 23:33 ` Minchan Kim
[not found] ` <CAHqPoqKZFDSjO1pL+ixYe_m_L0nGNcu04qSNp-jd1fUixKtHnw@mail.gmail.com>
2015-01-29 2:01 ` Minchan Kim
2015-01-29 2:22 ` Sergey Senozhatsky
2015-01-29 5:28 ` Minchan Kim
2015-01-29 6:06 ` Sergey Senozhatsky
2015-01-29 6:35 ` Minchan Kim
2015-01-29 7:08 ` Sergey Senozhatsky
2015-01-30 14:41 ` Minchan Kim
2015-01-31 11:31 ` Sergey Senozhatsky
2015-02-01 14:50 ` Sergey Senozhatsky
2015-02-01 15:04 ` Sergey Senozhatsky
2015-02-02 1:43 ` Minchan Kim
2015-02-02 1:59 ` Sergey Senozhatsky
2015-02-02 2:45 ` Minchan Kim
2015-02-02 3:47 ` Sergey Senozhatsky
2015-02-02 1:30 ` Minchan Kim
2015-02-02 1:48 ` Sergey Senozhatsky
2015-02-02 2:44 ` Minchan Kim
2015-02-02 4:01 ` Sergey Senozhatsky
2015-02-02 4:28 ` Minchan Kim
2015-02-02 5:09 ` Sergey Senozhatsky
2015-02-02 5:18 ` Minchan Kim
2015-02-02 5:28 ` Sergey Senozhatsky
2015-02-02 5:10 ` Minchan Kim
2015-01-30 0:20 ` Sergey Senozhatsky
2015-01-29 13:48 ` Ganesh Mahendran
2015-01-29 15:12 ` Sergey Senozhatsky
2015-01-30 7:52 ` Ganesh Mahendran
2015-01-30 8:08 ` Sergey Senozhatsky
2015-01-31 8:50 ` Ganesh Mahendran
2015-01-31 11:07 ` Sergey Senozhatsky
2015-01-31 12:59 ` Ganesh Mahendran [this message]
2015-02-02 3:41 Minchan Kim
2015-02-02 5:59 ` Sergey Senozhatsky
2015-02-02 6:18 ` Minchan Kim
2015-02-02 7:06 ` Sergey Senozhatsky
2015-02-03 1:54 ` Sergey Senozhatsky
2015-02-03 3:02 ` Minchan Kim
2015-02-03 3:56 ` Sergey Senozhatsky
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