Re: [Qemu-devel] [PATCH 1/2] nbd: Drop connection if broken server is detected

[Eric Blake <eblake@redhat.com>]

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On 08/11/2017 02:41 PM, Eric Blake wrote:
>> Hmm, was it correct even before your patch? Is it safe to enter a coroutine
>> (which we've scheduled by nbd_recv_coroutines_enter_all()), which is
>> actually
>> yielded inside nbd_rwv (not our yield in nbd_co_receive_reply)?
> 
> I'm honestly not sure how to answer the question. In my testing, I was
> unable to catch a coroutine yielding inside of nbd_rwv();

Single stepping through nbd_rwv(), I see that I/O is performed by
sendmsg(), which either gets the message sent or, because of nonblocking
mode, fails with EAGAIN, which gets turned into QIO_CHANNEL_ERR_BLOCK
and indeed a call to qemu_channel_yield() within nbd_rwv() - but it's
timing sensitive, so I still haven't been able to provoke this scenario
using gdb.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org


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