Re: [PATCH] net/ipv4: fix tcp_poll for SMC fallback

From: Karsten Graul <redacted>
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 <redacted>

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.