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Re: [Qemu-block] [PATCH 11/11] block/snapshot: do not take AioContext lo
Re: [Qemu-block] [PATCH 11/11] block/snapshot: do not take AioContext lock
Wed, 12 Jul 2017 11:42:02 +0100
On Tue, Jul 11, 2017 at 11:48:02AM +0200, Paolo Bonzini wrote:
> On 11/07/2017 11:43, Stefan Hajnoczi wrote:
> >>> 1. Must be called under BQL?
> >>> 2. Can I/O requests be in flight?
> >>> 3. Is it thread-safe?
> >>> Otherwise it will be a nightmare to modify the code since these
> >>> constraints are not enforced by the compiler and undocumented.
> >> Good point. Are (1) and (3) different ways to say the same thing or do
> >> you have other differences in mind?
> > There is a difference between (1) and (3). If a function is thread-safe
> > then callers can invoke it without any constraints. If a function
> > requires a specific lock to be held then that it puts a constraint on
> > the caller.
> > We do have thread-safe functions in the block layer: simple functions
> > that fetch a BDS field atomically. There is no need to hold the BQL for
> > them.
> Ok, so we are in (somewhat violent) agreement. "It's not thread-safe"
> pretty much means "must be called under BQL".
> I look forward to extending Marc-André's -Wthread-safety experiments to
> cover bdrv_drained_begin/end!
Sounds good :).
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Re: [Qemu-block] [Qemu-devel] [RFC PATCH 00/11] Block layer thread-safety, next part, no-reply, 2017/07/06
Re: [Qemu-block] [RFC PATCH 00/11] Block layer thread-safety, next part, Stefan Hajnoczi, 2017/07/10
- Re: [Qemu-block] [PATCH 07/11] block: do not acquire AioContext in check_to_replace_node, (continued)