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--die-with-parent is a massive footgun

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Assessment

Difficulty
2/5
Estimated time
1-3 hours
Newbie friendliness
35/100
Issue type
Documentation
Clarity
Mostly clear
Activity status
Stale
Tech stack
c, linux
Domain
operating-systems

Research direction

Start by locating the documentation for the --die-with-parent option and read the related discussion in #633. Confirm how the documentation describes parent-thread termination and the race, then update it to reflect the reported behavior and clarify the risks; the issue also raises whether the option should be removed, which needs maintainer direction.

Written by the indexing model from the issue text.

Description

I recently stumbled upon the same issue that was reported in this blog post: https://www.recall.ai/blog/pdeathsig-is-almost-never-what-you-want.

The problem is how PR_SET_PDEATHSIG works (from here):

The parent-death signal is sent upon subsequent termination of the parent thread

Thus it is triggered by the death of the parent thread, not the parent process. This means that if the parent process chooses to launch a subprocess using a thread that isn't the main thread, and then that thread happens to die, then bwrap and its children will receive a SIGKILL, even though the parent process is still alive. This can lead to some very hard to debug process deaths.

I was running bwrap --die-with-parent in a Docker container via docker exec. Docker ultimately invokes runc to create processes, and runc is evidently multi-threaded, because I would occasionally get these SIGKILL process deaths.

I don't think this is adequately explained in Bubblewrap's documentation, which says this:

    --die-with-parent            Kills with SIGKILL child process (COMMAND) when bwrap or bwrap's parent dies.

Considering this flag is also inherently racy (see #633) I feel like it's dangerous to use and maybe should even be removed.

Dominant language
C
Stars
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Forks
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Avg merge
1d 23h
Merged PRs (30d)
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