Re: [PATCH] SUNRPC: Use poll() to fix up the socket requeue races

[Chuck Lever <chuck.lever@oracle.com>]

> On Feb 19, 2019, at 10:13 AM, Trond Myklebust <trondmy@hammerspace.com> wrote:
> 
> On Tue, 2019-02-19 at 09:54 -0500, Chuck Lever wrote:
>> Hi Trond-
>> 
>>> On Feb 19, 2019, at 9:06 AM, Trond Myklebust <trondmy@gmail.com>
>>> wrote:
>>> 
>>> Because we clear XPRT_SOCK_DATA_READY before reading, we can end up
>>> with a situation where new data arrives, causing xs_data_ready() to
>>> queue up a second receive worker job for the same socket, which
>>> then
>>> immediately gets stuck waiting on the transport receive mutex.
>>> The fix is to only clear XPRT_SOCK_DATA_READY once we're done
>>> reading,
>>> and then to use poll() to check if we might need to queue up a new
>>> job in order to deal with any new data.
>> 
>> Does this fix an application-visible hang, or is it merely a
>> performance
>> optimization?
> 
> I'm not aware of any hang associated with this behaviour. The patch is
> rather intended as an optimisation to avoid having these threads block
> uselessly on a mutex.

That was my guess, thanks, just wanted to make certain.

--
Chuck Lever