From: "Guilherme G. Piccoli" <guilherme@gpiccoli.net>
To: Wols Lists <antlists@youngman.org.uk>, Song Liu <liu.song.a23@gmail.com>
Cc: "Guilherme G. Piccoli" <gpiccoli@canonical.com>,
linux-block@vger.kernel.org,
linux-raid <linux-raid@vger.kernel.org>,
dm-devel@redhat.com, axboe@kernel.dk,
Gavin Guo <gavin.guo@canonical.com>,
Jay Vosburgh <jay.vosburgh@canonical.com>,
kernel@gpiccoli.net, Ming Lei <ming.lei@redhat.com>,
Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
stable@vger.kernel.org
Subject: Re: [PATCH 2/2] md/raid0: Do not bypass blocking queue entered for raid0 bios
Date: Wed, 8 May 2019 11:52:29 -0300 [thread overview]
Message-ID: <0ad36b2f-ec36-6930-b587-da0526613567@gpiccoli.net> (raw)
In-Reply-To: <5CD2A172.4010302@youngman.org.uk>
On 5/8/19 6:29 AM, Wols Lists wrote:
> On 06/05/19 22:07, Song Liu wrote:
>> Could you please run a quick test with raid5? I am wondering whether
>> some race condition could get us into similar crash. If we cannot easily
>> trigger the bug, we can process with this version.
>
> Bear in mind I just read the list and write documentation, but ...
>
> My gut feeling is that if it can theoretically happen for all raid
> modes, it should be fixed for all raid modes. What happens if code
> changes elsewhere and suddenly it really does happen for say raid-5?
>
> On the other hand, if fixing it in md.c only gets tested for raid-0, how
> do we know it will actually work for other raids if they do suddenly
> start falling through.
Hi, I understand your concern. But all other raid levels contains
failure-event mechanisms. For example, in all my tests with raid5 or
raid1, it first complained the device was removed, then it failed in
super_written() when no other available device was present.
On the other hand, raid0 does "blind-writes": it just selects the device
in which that bio should be written (given the stripe math) and change
the bio's device, sending it back via generic_make_request(). It's
dummy, but not in a bad way, but rather for performance reasons. It has
no "intelligence" for failures, as all other raid levels.
That said, we could fix md.c for all raid levels, but I personally think
it's a bazooka shot, only raid0 shows consistently this issue.
>
> Academic purity versus engineering practicality :-)
Heheh you have good points here! Thanks for the input =)
Cheers,
Guilherme
>
> Cheers,
> Wol
>
next prev parent reply other threads:[~2019-05-08 14:52 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-04-30 22:37 [PATCH 1/2] block: Fix a NULL pointer dereference in generic_make_request() Guilherme G. Piccoli
2019-04-30 22:37 ` [PATCH 2/2] md/raid0: Do not bypass blocking queue entered for raid0 bios Guilherme G. Piccoli
2019-05-06 16:50 ` Song Liu
2019-05-06 18:48 ` Guilherme G. Piccoli
2019-05-06 21:07 ` Song Liu
2019-05-07 21:51 ` Guilherme G. Piccoli
2019-05-08 9:29 ` Wols Lists
2019-05-08 14:52 ` Guilherme G. Piccoli [this message]
2019-05-08 16:52 ` Wols Lists
2019-05-17 16:19 ` Guilherme G. Piccoli
2019-05-20 16:23 ` Song Liu
2019-05-20 19:25 ` Guilherme Piccoli
2019-04-30 22:55 ` [PATCH 1/2] block: Fix a NULL pointer dereference in generic_make_request() Bart Van Assche
2019-05-17 3:33 ` Eric Ren
2019-05-17 16:17 ` Guilherme G. Piccoli
2019-05-20 2:43 ` Eric Ren
2019-05-17 22:04 ` Ming Lei
2019-05-23 17:23 Song Liu
2019-05-23 17:23 ` [PATCH 2/2] md/raid0: Do not bypass blocking queue entered for raid0 bios Song Liu
2019-06-12 12:40 ` Guilherme Piccoli
2019-06-12 12:48 ` Greg KH
2019-06-12 16:38 ` Guilherme G. Piccoli
2019-06-12 16:37 ` Guilherme G. Piccoli
2019-06-12 16:49 ` Greg KH
2019-06-12 18:07 ` Guilherme Piccoli
2019-06-12 18:36 ` Greg KH
2019-06-12 18:43 ` Sasha Levin
2019-06-12 18:48 ` Guilherme Piccoli
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