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Re: [Qemu-devel] [PATCH for-2.9 3/5] block: Quiesce old aio context duri
From: |
Fam Zheng |
Subject: |
Re: [Qemu-devel] [PATCH for-2.9 3/5] block: Quiesce old aio context during bdrv_set_aio_context |
Date: |
Fri, 7 Apr 2017 07:44:26 +0800 |
User-agent: |
Mutt/1.8.0 (2017-02-23) |
On Thu, 04/06 17:17, Kevin Wolf wrote:
> Am 06.04.2017 um 16:25 hat Fam Zheng geschrieben:
> > The fact that the bs->aio_context is changing can confuse the dataplane
> > iothread, because of the now fine granularity aio context lock.
> > bdrv_drain should rather be a bdrv_drained_begin/end pair, but since
> > bs->aio_context is changing, we can just use aio_disable_external and
> > block_job_pause.
> >
> > Reported-by: Ed Swierk <address@hidden>
> > Signed-off-by: Fam Zheng <address@hidden>
> > ---
> > block.c | 11 +++++++++--
> > 1 file changed, 9 insertions(+), 2 deletions(-)
> >
> > diff --git a/block.c b/block.c
> > index 8893ac1..e70684a 100644
> > --- a/block.c
> > +++ b/block.c
> > @@ -4395,11 +4395,14 @@ void bdrv_attach_aio_context(BlockDriverState *bs,
> >
> > void bdrv_set_aio_context(BlockDriverState *bs, AioContext *new_context)
> > {
> > - AioContext *ctx;
> > + AioContext *ctx = bdrv_get_aio_context(bs);
> >
> > + aio_disable_external(ctx);
> > + if (bs->job) {
> > + block_job_pause(bs->job);
> > + }
>
> Even more bs->job users... :-(
>
> But is this one actually necessary? We drain all pending BHs below, so
> the job shouldn't have any requests in flight or be able to submit new
> ones while we switch.
I'm not 100% sure, but I think the aio_poll() loop below can still fire
co_sleep_cb if we don't do block_job_pause()?
>
> > bdrv_drain(bs); /* ensure there are no in-flight requests */
> >
> > - ctx = bdrv_get_aio_context(bs);
> > while (aio_poll(ctx, false)) {
> > /* wait for all bottom halves to execute */
> > }
> > @@ -4412,6 +4415,10 @@ void bdrv_set_aio_context(BlockDriverState *bs,
> > AioContext *new_context)
> > aio_context_acquire(new_context);
> > bdrv_attach_aio_context(bs, new_context);
> > aio_context_release(new_context);
> > + if (bs->job) {
> > + block_job_resume(bs->job);
> > + }
> > + aio_enable_external(ctx);
> > }
>
> The aio_disabe/enable_external() pair seems to make sense anyway.
>
> Kevin