Re: [PATCH 0/3] signal: requeuing undeliverable signals

Kyle Huey [off-list ref] writes:

On Mon, Nov 15, 2021 at 9:31 PM Eric W. Biederman [off-list ref] wrote:

quoted

Kyle Huey recently reported[1] that rr gets confused if SIGKILL prevents
ptrace_signal from delivering a signal, as the kernel setups up a signal
frame for a signal that rr did not have a chance to observe with ptrace.

In looking into it I found a couple of bugs and a quality of
implementation issue.

- The test for signal_group_exit should be inside the for loop in get_signal.
- Signals should be requeued on the same queue they were dequeued from.
- When a fatal signal is pending ptrace_signal should not return another
  signal for delivery.

Kyle Huey has verified[2] an earlier version of this change.

I have reworked things one more time to completely fix the issues
raised, and to keep the code maintainable long term.

I have smoke tested this code and combined with a careful review I
expect this code to work fine.  Kyle if you can double check that
my last round of changes still works for rr I would appreciate it.

This still fixes the race we reported.

Tested-by: Kyle Huey <redacted>

Thank you very much for retesting.

Eric