linux-kernel - RE: [PATCH] drbd: do not ignore signals in threads

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Message-ID: <1fcbb94c5f264c17af3394807438ad50@AcuMS.aculab.com>
Date:   Mon, 12 Aug 2019 13:12:16 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Philipp Reisner' <philipp.reisner@...bit.com>,
        Jens Axboe <axboe@...nel.dk>
CC:     'Christoph Böhmwalder' 
        <christoph.boehmwalder@...bit.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        "Eric W . Biederman" <ebiederm@...ssion.com>
Subject: RE: [PATCH] drbd: do not ignore signals in threads

From: Philipp Reisner
> Sent: 12 August 2019 12:53
> Hi Jens,
> 
> Please have a look.
> 
> With fee109901f392 Eric W. Biederman changed drbd to use send_sig()
> instead of force_sig(). That was part of a series that did this change
> in multiple call sites tree wide. Which, by accident broke drbd, since
> the signals are _not_ allowed by default. That got released with v5.2.
> 
> On July 29 Christoph 	Böhmwalder sent a patch that adds two
> allow_signal()s to fix drbd.
> 
> Then David Laight points out that he has code that can not deal
> with the send_sig() instead of force_sig() because allowed signals
> can be sent from user-space as well.
> I assume that David is referring to out of tree code, so I fear it
> is up to him to fix that to work with upstream, or initiate a
> revert of Eric's change.

While our code is 'out of tree' (you really don't want it - and since
it still uses force_sig() is fine) I suspect that the 'drdb' code
(with Christoph's allow_signal() patch) now loops in kernel if a user
sends it a signal.

If the driver (eg drdb) is using (say) SIGINT to break a thread out of
(say) a blocking kernel_accept() call then it can detect the unexpected
signal (maybe double-checking with signal_pending()) but I don't think
it can clear down the pending signal so that kernel_accept() blocks
again.

> Jens, please consider sending Christoph's path to Linus for merge in
> this cycle, or let us know how you think we should proceed.

I'm not sure what the 'correct' solution is.

	David

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