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Re: [Qemu-devel] [PATCH v2 for-2.11 2/4] coroutine: abort if we try to s
From: |
Kevin Wolf |
Subject: |
Re: [Qemu-devel] [PATCH v2 for-2.11 2/4] coroutine: abort if we try to schedule or enter a pending coroutine |
Date: |
Tue, 21 Nov 2017 14:47:54 +0100 |
User-agent: |
Mutt/1.9.1 (2017-09-22) |
Am 21.11.2017 um 03:23 hat Jeff Cody geschrieben:
> The previous patch fixed a race condition, in which there were
> coroutines being executing doubly, or after coroutine deletion.
>
> We can detect common scenarios when this happens, and print an error
> message and abort before we corrupt memory / data, or segfault.
>
> This patch will abort if an attempt to enter a coroutine is made while
> it is currently pending execution, either in a specific AioContext bh,
> or pending execution via a timer. It will also abort if a coroutine
> is scheduled, before a prior scheduled run has occured.
>
> We cannot rely on the existing co->caller check for recursive re-entry
> to catch this, as the coroutine may run and exit with
> COROUTINE_TERMINATE before the scheduled coroutine executes.
>
> (This is the scenario that was occuring and fixed in the previous
> patch).
>
> Signed-off-by: Jeff Cody <address@hidden>
> ---
> include/qemu/coroutine_int.h | 6 ++++++
> util/async.c | 11 +++++++++++
> util/qemu-coroutine-sleep.c | 11 +++++++++++
> util/qemu-coroutine.c | 11 +++++++++++
> 4 files changed, 39 insertions(+)
>
> diff --git a/include/qemu/coroutine_int.h b/include/qemu/coroutine_int.h
> index cb98892..56e4c48 100644
> --- a/include/qemu/coroutine_int.h
> +++ b/include/qemu/coroutine_int.h
> @@ -53,6 +53,12 @@ struct Coroutine {
>
> /* Only used when the coroutine has yielded. */
> AioContext *ctx;
> +
> + /* Used to catch and abort on illegal co-routine entry.
> + * Will contain the name of the function that had first
> + * scheduled the coroutine. */
> + const char *scheduled;
Not sure if it makes any difference in practice, but I just want to
mention that the new field is right after a cacheline boundary and
the only field that is used in qemu_aio_coroutine_enter() and accesses
this second cacheline.
I'm not paying much attention to this kind of thing in most contexts,
but entering a coroutine is a hot path that we want to be fast, so maybe
it's worth having a second look.
Kevin