netdev - Re: [PATCH] net/ipv4: fix tcp

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Date:   Thu, 18 Oct 2018 11:22:04 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     kgraul@...ux.ibm.com
Cc:     netdev@...r.kernel.org, ubraun@...ux.ibm.com, hch@....de,
        linux-s390@...r.kernel.org
Subject: Re: [PATCH] net/ipv4: fix tcp_poll for SMC fallback

From: Karsten Graul <kgraul@...ux.ibm.com>
Date: Tue, 16 Oct 2018 16:45:54 +0200

> Commit dd979b4df817 ("net: simplify sock_poll_wait") breaks tcp_poll for 
> SMC fallback: An AF_SMC socket establishes an internal TCP socket for the 
> CLC handshake with the remote peer. Whenever the SMC connection can not be 
> established this CLC socket is used as a fallback. All socket operations on the 
> SMC socket are then forwarded to the CLC socket. In case of poll, the 
> file->private_data pointer references the SMC socket because the CLC socket has 
> no file assigned. This causes tcp_poll to wait on the wrong socket.
> 
> This patch fixes the issue by (re)introducing a sock_poll_wait variant with 
> a socket parameter, and let tcp_poll use this variant.
> 
> Fixes: dd979b4df817 ("net: simplify sock_poll_wait")
> Signed-off-by: Karsten Graul <kgraul@...ux.ibm.com>

Generally speaking, if the invariant of filp->private_data == sock
does not actually hold true universally, I'd rather revert the
simplifications and add a big comment to sock_poll_wait() explaining
this.

Thank you.