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

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Date:   Mon, 12 Aug 2019 15:28:40 +0200
From:   Philipp Reisner <philipp.reisner@...bit.com>
To:     David Laight <David.Laight@...lab.com>
Cc:     Jens Axboe <axboe@...nel.dk>,
        '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

Hi David,

[...]
> 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.

I am not asking for that out of tree code. But you are welcome to learn
from the drbd code that is in the upstream kernel.
It does not loop if a root sends a signal, it receives it and ignores it.

> 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.

You do that with flush_signals(current)

What we have do is, somewhere in the main loop:

  if (signal_pending(current)) {
			flush_signals(current);
			if (!terminate_condition()) {
				warn(connection, "Ignoring an unexpected signal\n");
				continue;
			}
			break;
		}
  }

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