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From: Paolo Bonzini <pbonzini@redhat.com>
To: Max Reitz <mreitz@redhat.com>,
	"qemu-devel@nongnu.org" <qemu-devel@nongnu.org>
Cc: Kevin Wolf <kwolf@redhat.com>, Stefan Hajnoczi <stefanha@redhat.com>
Subject: Re: Thread safety of coroutine-sigaltstack
Date: Wed, 20 Jan 2021 17:50:48 +0100	[thread overview]
Message-ID: <7f480097-e1d0-1cec-9bff-dd9f8d847dff@redhat.com> (raw)
In-Reply-To: <7b8155ad-0942-dc1c-f43c-bb5eb518a278@redhat.com>

On 20/01/21 17:26, Max Reitz wrote:
> Now, this all seems obvious to me, but I’m wondering...  If 
> coroutine-sigaltstack really couldn’t create coroutines concurrently,
>  why wouldn’t we have noticed before?  I mean, this new backup case
> is kind of a stress test, yes, but surely we would have seen the
> problem already, right?  That’s why I’m not sure whether my analysis
> is correct.

Probably the BQL was hiding the issue?

> Anyway, I’ve attached a patch that wraps the whole
> SIGUSR2 handling section in a mutex, and that makes 256 pass reliably
> with Vladimir’s async backup series.  Besides being unsure whether
> the problem is really in coroutine-sigaltstack, I also don’t know
> whether getting out the big guns and wrapping everything in the mutex
> is the best solution.  So, it’s an RFC, I guess.

I think that's fine.  The coroutine pool will hide scalability issues.

Paolo



  reply	other threads:[~2021-01-20 16:53 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-20 16:26 Thread safety of coroutine-sigaltstack Max Reitz
2021-01-20 16:50 ` Paolo Bonzini [this message]
2021-01-20 16:58 ` Eric Blake
2021-01-20 17:25 ` Laszlo Ersek
2021-01-21  9:27   ` Max Reitz
2021-01-21 13:34     ` Laszlo Ersek
2021-01-21 15:42       ` Max Reitz
2021-01-21 16:04         ` Daniel P. Berrangé
2021-01-21 16:05         ` Laszlo Ersek
2021-01-21 15:14     ` Paolo Bonzini
2021-01-21 16:07       ` Daniel P. Berrangé
2021-01-21 16:44         ` Peter Maydell
2021-01-21 17:24           ` Paolo Bonzini
2021-01-22 20:38             ` Laszlo Ersek
2021-01-22 21:34               ` Laszlo Ersek
2021-01-22 21:41                 ` Laszlo Ersek
2021-01-22  7:55       ` Markus Armbruster
2021-01-22  8:48   ` Max Reitz
2021-01-22 10:14     ` Peter Maydell
2021-01-22 10:16       ` Max Reitz
2021-01-22 12:24       ` Laszlo Ersek
2021-01-23  0:06       ` Laszlo Ersek
2021-01-23 13:35         ` Peter Maydell
2021-01-25 22:15           ` Laszlo Ersek
2021-01-25 22:45             ` Paolo Bonzini
2021-01-26  8:57               ` Laszlo Ersek

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