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Re: [libvirt] [PATCH] rpc: Fix client crash when server drops connection



On Tue, Mar 26, 2013 at 10:17:01 -0600, Eric Blake wrote:
> On 03/26/2013 09:52 AM, Jiri Denemark wrote:
> > Despite of the comment stating virNetClientIncomingEvent handler should
> 
> s/of //
> 
> > never be called with either client->haveTheBuck or client->wantClose
> > set, there is a sequence of events that may lead to both booleans being
> > true when virNetClientIncomingEvent is called. However, when that
> > happens, we must not immediately close the socket as there are other
> > threads waiting for the buck and they would cause SIGSEGV once they are
> > woken up after the socket was closed. Another thing is we should clear
> > all remaining calls in the queue after closing the socket.
> > 
> > The situation that can lead to the crash involves three threads, one of
> > them running event loop and the other two calling libvirt APIs. The
> > event loop threads detects an event on client->sock and calls
> > virNetClientIncomingEvent handler. But before the handler gets a chance
> > to lock client, the other two threads (T1 and T2) start calling some
> > APIs. T1 gets the buck and detects EOF on client->sock while processing
> > its RPC call. Since T2 is waiting for its own call, T1 passes the buck
> > onto it and unlocks client. But before T2 gets the signal, the event
> 
> s/onto/on to/
> 
> > loop thread wakes up, does its job and closes client->sock. The crash
> > happens when T2 actually wakes up and tries to do its job using a closed
> > client->sock.
> > ---
> >  src/rpc/virnetclient.c | 7 +++++--
> >  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> Tricky analysis, but I agree with the outcome.  Definitely worth fixing
> in 1.0.4.
> 
> ACK.

Thanks, I fixed one more typo in the commit message and pushed.

Jirka


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