linux-kernel - Re: [PATCH] tty: Fix pty master read() after slave closes

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Message-ID: <5245C12E.6070608@hurleysoftware.com>
Date:	Fri, 27 Sep 2013 13:32:30 -0400
From:	Peter Hurley <peter@...leysoftware.com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Mikael Pettersson <mikpelinux@...il.com>
CC:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tty: Fix pty master read() after slave closes

On 09/27/2013 01:27 PM, Peter Hurley wrote:
> Commit f95499c3030fe1bfad57745f2db1959c5b43dca8,
>    n_tty: Don't wait for buffer work in read() loop
> creates a race window which can cause a pty master read()
> to miss the last pty slave write(s) and return -EIO instead,
> thus signalling the pty slave is closed. This can happen when
> the pty slave is written and immediately closed but before the
> tty buffer i/o loop receives the new input; the pty master
> read() is scheduled, sees its read buffer is empty and the
> pty slave has been closed, and exits.
>
> Because tty_flush_to_ldisc() has significant performance impact
> for parallel i/o, rather than revert the commit, special case this
> condition (ie., when the read buffer is empty and the 'other' pty
> has been closed) and, only then, wait for buffer work to complete
> before re-testing if the read buffer is still empty.
>
> As before, subsequent pty master reads return any available data
> until no more data is available, and then returns -EIO to
> indicate the pty slave has closed.
>
> Reported-by: Mikael Pettersson <mikpelinux@...il.com>
> Signed-off-by: Peter Hurley <peter@...leysoftware.com>

I tested this patch with the gcc ada ACATS testsuite and got this
summary so all seems ok with this patch.

		=== acats Summary ===
# of expected passes		805
# of unexpected failures	0

...

		=== acats Summary ===
# of expected passes		772
# of unexpected failures	0

...

		=== acats Summary ===
# of expected passes		743
# of unexpected failures	0

Mikael,

I'd appreciate if you could re-test with this patch and
confirm the issue is fixed.

Regards,
Peter Hurley
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