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
On Wed, Nov 17, 2021 at 6:51 PM Eric W. Biederman [off-list ref] wrote:
Kyle Huey [off-list ref] writes:
quoted
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.
quoted
Tested-by: Kyle Huey <redacted>
Thank you very much for retesting.
Eric
Thank you, Kyle and Eric, for reporting and fixing the root cause of this race.
Meanwhile, I followed Kyle's suggestion and will disable the crash
handlers in the tracee whenever it is being traced.
Marko
--
Marko Mäkelä, Lead Developer InnoDB
MariaDB Corporation