Re: [Qemu-devel] [PATCH] sheepdog: discard the payload if the header is invalid

[Liu Yuan <namei.unix@gmail.com>]

On Mon, Aug 31, 2015 at 09:51:00PM -0400, Jeff Cody wrote:
> On Tue, Sep 01, 2015 at 09:29:31AM +0800, Liu Yuan wrote:
> > From: Liu Yuan <liuyuan@cmss.chinamobile.com>
> > 
> > We need to discard the payload if we get a invalid header due to whatever reason
> > to avoid data stream curruption.
> 
> If the header is invalid / corrupted, how can rsp.data_length be
> trusted?  Out of curiosity, is this an issue you are seeing occur "in
> the wild"?

This is the defensive patch. Header is invalid in the sense that only rsp.id is
invalid due to sheepdog driver bugs, for e.g., the request was misplaced after
being sent or duplicated requests sending to sheep daemon and get the duplicated
responses for the same request.

Actually in the late 2012 we had seen this problem but we didn't find the root
cause how this happened by looking at the code statically and the problem was
gone silently while we restructured the code.

But yesterday some centos6 users reported to me the problem of
'cannot find aio_req' and hang the guest disk. That QEMU's sheepdog driver was
rather old and would bump rsp.id mismatch problem as we did in the late 2012.
By looking at the code again, I found this error handling problem. However,
this patch is not aimed to solve the rsp.id mismatch problem (If it still exist)
but just a defensive one after this problem happens.

Thanks,
Yuan