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From:   Wen Gu <guwen@linux.alibaba.com>
To:     kgraul@linux.ibm.com, tonylu@linux.alibaba.com
Cc:     davem@davemloft.net, kuba@kernel.org, linux-s390@vger.kernel.org,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
        dust.li@linux.alibaba.com, xuanzhuo@linux.alibaba.com,
        guwen@linux.alibaba.com
Subject: [RFC PATCH 0/2] Two RFC patches for the same SMC socket wait queue mismatch issue
Date:   Wed, 10 Nov 2021 20:50:49 +0800
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Hi, Karsten

Thanks for your reply. The previous discussion about the issue of socket
wait queue mismatch in SMC fallback can be referred from:
https://lore.kernel.org/all/db9acf73-abef-209e-6ec2-8ada92e2cfbc@linux.ibm.com/

This set of patches includes two RFC patches, they are both aimed to fix
the same issue, the mismatch of socket wait queue in SMC fallback.

In your last reply, I am suggested to add the complete description about
the intention of initial patch in order that readers can understand the
idea behind it. This has been done in "[RFC PATCH net v2 0/2] net/smc: Fix
socket wait queue mismatch issue caused by fallback" of this mail.

Unfortunately, I found a defect later in the solution of the initial patch
or the v2 patch mentioned above. The defect is about fasync_list and related
to 67f562e3e14 ("net/smc: transfer fasync_list in case of fallback").

When user applications use sock_fasync() to insert entries into fasync_list,
the wait queue they operate is smc socket->wq. But in initial patch or
the v2 patch, I swapped sk->sk_wq of smc socket and clcsocket in smc_create(),
thus the sk_data_ready / sk_write_space.. of smc will wake up clcsocket->wq
finally. So the entries added into smc socket->wq.fasync_list won't be woken
up at all before fallback.

So the solution in initial patch or the v2 patch of this mail by swapping
sk->sk_wq of smc socket and clcsocket seems a bad way to fix this issue.

Therefore, I tried another solution by removing the wait queue entries from
smc socket->wq to clcsocket->wq during the fallback, which is described in the
"[RFC PATCH net 2/2] net/smc: Transfer remaining wait queue entries" of this
mail. In our test environment, this patch can fix the fallback issue well.

I am looking forward to hear your opinions. Thank you.

Cheers,
Wen Gu

Wen Gu (2):
  net/smc: Fix socket wait queue mismatch issue caused by fallback
  net/smc: Transfer remaining wait queue entries