[PATCH 4/4] net/tls: implement ->read_sock()

[Jakub Kicinski]

On Tue, 20 Jun 2023 16:21:22 +0300 Sagi Grimberg wrote:
> > +	err = tls_rx_reader_lock(sk, ctx, true);
> > +	if (err < 0)
> > +		return err;  
> 
> Unlike recvmsg or splice_read, the caller of read_sock is assumed to
> have the socket locked, and tls_rx_reader_lock also calls lock_sock,
> how is this not a deadlock?

Yeah :|

> I'm not exactly clear why the lock is needed here or what is the subtle
> distinction between tls_rx_reader_lock and what lock_sock provides.

It's a bit of a workaround for the consistency of the data stream.
There's bunch of state in the TLS ULP and waiting for mem or data
releases and re-takes the socket lock. So to stop the flow annoying
corner case races I slapped a lock around all of the reader.

IMHO depending on the socket lock for anything non-trivial and outside
of the socket itself is a bad idea in general.

The immediate need at the time was that if you did a read() and someone
else did a peek() at the same time from a stream of A B C D you may read
A D B C.