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Re: [Qemu-devel] [RFC v3 01/27] char-io: fix possible race on IOWatchPol

From: Fam Zheng
Subject: Re: [Qemu-devel] [RFC v3 01/27] char-io: fix possible race on IOWatchPoll
Date: Tue, 7 Nov 2017 14:43:28 +0800
User-agent: Mutt/1.9.1 (2017-09-22)

On Mon, 11/06 17:46, Peter Xu wrote:
> This is not a problem if we are only having one single loop thread like
> before.  However, after per-monitor thread is introduced, this is not
> true any more, and the race can happen.
> The race can be triggered with "make check -j8" sometimes:
>   qemu-system-x86_64: /root/git/qemu/chardev/char-io.c:91:
>   io_watch_poll_finalize: Assertion `iwp->src == NULL' failed.
> This patch keeps the reference for the watch object when creating in
> io_add_watch_poll(), so that the object will never be released in the
> context main loop, especially when the context loop is running in
> another standalone thread.  Meanwhile, when we want to remove the watch
> object, we always first detach the watch object from its owner context,
> then we continue with the cleanup.
> Without this patch, calling io_remove_watch_poll() in main loop thread
> is not thread-safe, since the other per-monitor thread may be modifying
> the watch object at the same time.

Looks sane,

Reviewed-by: Fam Zheng <address@hidden>

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