forked from lix-project/lix
darwin: workaround PROC_PIDLISTFDS on processes with no fds
This has been causing various seemingly spurious CI failures as well as
some failures on people running tests on beta builds.
lix> ++(nix-collect-garbage-dry-run.sh:20) nix-store --gc --print-dead
lix> ++(nix-collect-garbage-dry-run.sh:20) wc -l
lix> finding garbage collector roots...
lix> error: Listing pid 87261 file descriptors: Undefined error: 0
There is no real way to write a proper test for this, other than to
start a process like the following:
int main(void) {
for (int i = 0; i < 1000; ++i) {
close(i);
}
sleep(10000);
}
and then let Lix's gc look at it.
I have a relatively high confidence this *will* fix the problem since I
have manually confirmed the behaviour of the libproc call is
as-unexpected, and it would perfectly explain the observed symptom.
Fixes: lix-project/lix#446
Change-Id: I67669b98377af17895644b3bafdf42fc33abd076
This commit is contained in:
parent
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15
doc/manual/rl-next/haunted-gc-macos.md
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15
doc/manual/rl-next/haunted-gc-macos.md
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@ -0,0 +1,15 @@
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---
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synopsis: "Fix unexpectedly-successful GC failures on macOS"
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cls: 1723
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issues: fj#446
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credits: jade
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category: Fixes
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---
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Has the following happened to you on macOS? This failure has been successfully eliminated, thanks to our successful deployment of advanced successful-failure detection technology (it's just `if (failed && errno == 0)`. Patent pending<sup>not really</sup>):
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```
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$ nix-store --gc --print-dead
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finding garbage collector roots...
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error: Listing pid 87261 file descriptors: Undefined error: 0
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```
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@ -56,12 +56,27 @@ void DarwinLocalStore::findPlatformRoots(UncheckedRoots & unchecked)
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while (fdBufSize > fds.size() * sizeof(struct proc_fdinfo)) {
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// Reserve some extra size so we don't fail too much
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fds.resize((fdBufSize + fdBufSize / 8) / sizeof(struct proc_fdinfo));
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errno = 0;
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fdBufSize = proc_pidinfo(
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pid, PROC_PIDLISTFDS, 0, fds.data(), fds.size() * sizeof(struct proc_fdinfo)
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);
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// errno == 0???! Yes, seriously. This is because macOS has a
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// broken syscall wrapper for proc_pidinfo that has no way of
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// dealing with the system call successfully returning 0. It
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// takes the -1 error result from the errno-setting syscall
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// wrapper and turns it into a 0 result. But what if the system
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// call actually returns 0? Then you get an errno of success.
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//
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// https://github.com/apple-opensource/xnu/blob/4f43d4276fc6a87f2461a3ab18287e4a2e5a1cc0/libsyscall/wrappers/libproc/libproc.c#L100-L110
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// https://git.lix.systems/lix-project/lix/issues/446#issuecomment-5483
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// FB14695751
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if (fdBufSize <= 0) {
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throw SysError("Listing pid %1% file descriptors", pid);
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if (errno == 0) {
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break;
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} else {
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throw SysError("Listing pid %1% file descriptors", pid);
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}
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}
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}
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fds.resize(fdBufSize / sizeof(struct proc_fdinfo));
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