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From: Roman Kagan <rvkagan@yandex-team.ru>
To: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Cc: Kevin Wolf <kwolf@redhat.com>,
	qemu-block@nongnu.org, qemu-devel@nongnu.org,
	Max Reitz <mreitz@redhat.com>,
	yc-core@yandex-team.ru
Subject: Re: [PATCH 7/7] block/nbd: stop manipulating in_flight counter
Date: Tue, 16 Mar 2021 19:08:13 +0300	[thread overview]
Message-ID: <YFDX7aZngRCZF9Ew@rvkaganb.lan> (raw)
In-Reply-To: <de4fd61f-ccd3-125b-b636-aa06efe5823a@virtuozzo.com>

On Mon, Mar 15, 2021 at 11:15:44PM +0300, Vladimir Sementsov-Ogievskiy wrote:
> 15.03.2021 09:06, Roman Kagan wrote:
> > As the reconnect logic no longer interferes with drained sections, it
> > appears unnecessary to explicitly manipulate the in_flight counter.
> > 
> > Fixes: 5ad81b4946 ("nbd: Restrict connection_co reentrance")
> 
> And here you actually allow qemu_aio_coroutine_enter() call in
> nbd_client_attach_aio_context_bh() to enter connection_co in any yield
> point which is possible during drained section. The analysis should be
> done to be sure that all these yield points are safe for reentering by
> external qemu_aio_coroutine_enter(). (By external I mean not by the
> actual enter() we are waiting for at the yield() point. For example
> qemu_channel_yield() supports reentering.. And therefore (as I
> understand after fast looking through) nbd_read() should support
> reentering too..

I'll do a more thorough analysis of how safe it is.

FWIW this hasn't triggered any test failures yet, but that assert in
patch 3 didn't ever go off either so I'm not sure I can trust the tests
on this.

Thanks,
Roman.


  reply	other threads:[~2021-03-16 16:18 UTC|newest]

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-15  6:06 [PATCH 0/7] block/nbd: decouple reconnect from drain Roman Kagan
2021-03-15  6:06 ` [PATCH 1/7] block/nbd: avoid touching freed connect_thread Roman Kagan
2021-03-15 15:40   ` Vladimir Sementsov-Ogievskiy
2021-03-16 15:29     ` Roman Kagan
2021-04-06 16:21   ` Vladimir Sementsov-Ogievskiy
2021-03-15  6:06 ` [PATCH 2/7] block/nbd: use uniformly nbd_client_connecting_wait Roman Kagan
2021-03-15 15:48   ` Vladimir Sementsov-Ogievskiy
2021-03-15  6:06 ` [PATCH 3/7] block/nbd: assert attach/detach runs in the proper context Roman Kagan
2021-03-15 16:41   ` Vladimir Sementsov-Ogievskiy
2021-03-15 19:57     ` Roman Kagan
2021-03-15  6:06 ` [PATCH 4/7] block/nbd: transfer reconnection stuff across aio_context switch Roman Kagan
2021-03-15  6:06 ` [PATCH 5/7] block/nbd: better document a case in nbd_co_establish_connection Roman Kagan
2021-03-15  6:06 ` [PATCH 6/7] block/nbd: decouple reconnect from drain Roman Kagan
2021-03-15 20:10   ` Vladimir Sementsov-Ogievskiy
2021-03-16 16:03     ` Roman Kagan
2021-03-16 18:09       ` Vladimir Sementsov-Ogievskiy
2021-03-26  6:16         ` Roman Kagan
2021-03-15  6:06 ` [PATCH 7/7] block/nbd: stop manipulating in_flight counter Roman Kagan
2021-03-15 20:15   ` Vladimir Sementsov-Ogievskiy
2021-03-16 16:08     ` Roman Kagan [this message]
2021-03-16 18:37       ` Vladimir Sementsov-Ogievskiy
2021-03-26  7:41         ` Roman Kagan
2021-03-15 19:45 ` [PATCH 0/7] block/nbd: decouple reconnect from drain Vladimir Sementsov-Ogievskiy
2021-03-16 15:52   ` Roman Kagan
2021-03-16 14:41 ` Eric Blake
2021-03-16 16:10   ` Roman Kagan
2021-03-17  8:35 ` Vladimir Sementsov-Ogievskiy
2021-03-26  8:07   ` Roman Kagan
2021-04-07  7:45   ` Roman Kagan
2021-04-07 10:13     ` Vladimir Sementsov-Ogievskiy

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