| commit | cd84ef30b6b6cdf4db75ac5307a79aeff999f9f7 | [log] [tgz] |
|---|---|---|
| author | jacobsa <jacobsa@google.com> | Wed Sep 23 02:23:25 2020 -0700 |
| committer | Copybara-Service <copybara-worker@google.com> | Wed Sep 23 02:24:25 2020 -0700 |
| tree | 411bbf5a9880139a2dcf3550810dba69a91d1efc | |
| parent | 731e87e9620c629d7506396f89726bb61825fc95 [diff] |
linux-sandbox-pid1: don't try to forward signals before forking.
This causes us to forward to PID 0, i.e. to ourselves. That in turn can cause
us to get into a 100% CPU loop under certain cases.
For example, the following sequence of events:
1. The root process (linux-sandbox.cc) spawns the child process
(linux-sandbox-pid1.cc).
2. The root process installs signal handlers, including a SIGTERM handler that
forwards SIGTERM and then calls alarm(2).
3. The root process never installs the specific SIGALRM handler, either
because timeout_secs is not positive or because it is delayed for a very
long time for whatever reason.
4. bazel sends SIGTERM to the root process. This is forwarded to the child,
which starts forwarding it to itself in a loop, because fork hasn't yet
returned. In the root process, an alarm is installed.
5. Eventually the alarm expires in the root process, and again it is forwarded
to the child.
6. The child is now forwarding both SIGTERM and SIGALRM to itself.
While I was at it, rationalized the signal forwarding behavior. SIGTERM is the
only one that seems to make sense to forward; even SIGALRM doesn't make sense
because we don't ask the kernel to give it to us in the first place, so we
never expect to receive it.
PiperOrigin-RevId: 333252396
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