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

[Max Reitz <mreitz@redhat.com>]

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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 <rjones@redhat.com>
> Cc: jcody@redhat.com
> Cc: qemu-stable@nongnu.org
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  block/curl.c | 13 ++++++++++++-
>  1 file changed, 12 insertions(+), 1 deletion(-)

Reviewed-by: Max Reitz <mreitz@redhat.com>


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