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Re: [PATCH v2 04/10] block/nbd: simplify waking of nbd_co_establish_conn

From: Roman Kagan
Subject: Re: [PATCH v2 04/10] block/nbd: simplify waking of nbd_co_establish_connection()
Date: Thu, 8 Apr 2021 19:10:46 +0300

On Thu, Apr 08, 2021 at 05:08:21PM +0300, Vladimir Sementsov-Ogievskiy wrote:
> Instead of connect_bh, bh_ctx and wait_connect fields we can live with
> only one link to waiting coroutine, protected by mutex.
> So new logic is:
> nbd_co_establish_connection() sets wait_co under mutex, release the
> mutex and do yield(). Note, that wait_co may be scheduled by thread
> immediately after unlocking the mutex. Still, in main thread (or
> iothread) we'll not reach the code for entering the coroutine until the
> yield() so we are safe.
> Both connect_thread_func() and nbd_co_establish_connection_cancel() do
> the following to handle wait_co:
> Under mutex, if thr->wait_co is not NULL, call aio_co_wake() (which
> never tries to acquire aio context since previous commit, so we are
> safe to do it under thr->mutex) and set thr->wait_co to NULL.
> This way we protect ourselves of scheduling it twice.
> Also this commit make nbd_co_establish_connection() less connected to
> bs (we have generic pointer to the coroutine, not use s->connection_co
> directly). So, we are on the way of splitting connection API out of
> nbd.c (which is overcomplicated now).
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> ---
>  block/nbd.c | 49 +++++++++----------------------------------------
>  1 file changed, 9 insertions(+), 40 deletions(-)

Reviewed-by: Roman Kagan <rvkagan@yandex-team.ru>

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