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From: NeilBrown <neilb@suse.com>
To: Mikulas Patocka <mpatocka@redhat.com>
Cc: dm-devel@redhat.com, Mike Snitzer <snitzer@redhat.com>,
	Alasdair Kergon <agk@redhat.com>
Subject: Re: [PATCH/rfc] dm: revise 'rescue' strategy for md->bs allocations
Date: Fri, 01 Sep 2017 13:48:40 +1000	[thread overview]
Message-ID: <87inh3dqp3.fsf@notabene.neil.brown.name> (raw)
In-Reply-To: <alpine.LRH.2.02.1708312233010.32309@file01.intranet.prod.int.rdu2.redhat.com>


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On Thu, Aug 31 2017, Mikulas Patocka wrote:

>> 
>> Note that only current->bio_list[0] is offloaded.  current->bio_list[1]
>> contains bios that were scheduled *before* the current one started, so
>
> These bios need to be offloaded too, otherwise you re-introduce this 
> deadlock: https://www.redhat.com/archives/dm-devel/2014-May/msg00089.html

Thanks for the link.
In the example the bio that is stuck was created in step 4.  The call
to generic_make_request() will have placed it on current->bio_list[0].
The top-level generic_make_request call by Process A is still running,
so nothing will have moved the bio to ->bio_list[1].  That only happens
after the ->make_request_fn completes, which must be after step 7.
So the problem bio is on ->bio_list[0] and the code in my patch will
pass it to a workqueue for handling.

So I don't think the deadlock would be reintroduced.  Can you see
something that I am missing?

Thanks,
NeilBrown

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next prev parent reply	other threads:[~2017-09-01  3:48 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-08-31  6:18 [PATCH/rfc] dm: revise 'rescue' strategy for md->bs allocations NeilBrown
2017-09-01  2:38 ` Mikulas Patocka
2017-09-01  3:48   ` NeilBrown [this message]
2017-09-02  1:34     ` Mikulas Patocka
2017-09-04  0:12       ` NeilBrown
2017-09-04 16:54         ` Mikulas Patocka
2017-09-05 23:43           ` NeilBrown
2017-09-06 22:57             ` Mikulas Patocka
2017-09-07  3:19               ` NeilBrown

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