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Re: [Qemu-block] [PATCH 3/7] curl: avoid recursive locking of BDRVCURLSt

From: Max Reitz
Subject: Re: [Qemu-block] [PATCH 3/7] curl: avoid recursive locking of BDRVCURLState mutex
Date: Wed, 10 May 2017 18:38:58 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.1.0

On 10.05.2017 16:32, Paolo Bonzini wrote:
> The curl driver has a ugly hack where, if it cannot find an empty CURLState,
> it just uses aio_poll to wait for one to be empty.  This is probably
> buggy when used together with dataplane, and the simplest way to fix it
> is to use coroutines instead.
> A more immediate effect of the bug however is that it can cause a
> recursive call to curl_readv_bh_cb and recursively taking the
> BDRVCURLState mutex.  This causes a deadlock.
> The fix is to unlock the mutex around aio_poll, but for cleanliness we
> should also take the mutex around all calls to curl_init_state, even if
> reaching the unlock/lock pair is impossible.  The same is true for
> curl_clean_state.
> Reported-by: Richard W.M. Jones <address@hidden>
> Cc: address@hidden
> Cc: address@hidden
> Signed-off-by: Paolo Bonzini <address@hidden>
> ---
>  block/curl.c | 13 ++++++++++++-
>  1 file changed, 12 insertions(+), 1 deletion(-)

Reviewed-by: Max Reitz <address@hidden>

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