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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