Ignore EPERM locking error if thread does not exist - #111
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benfred merged 3 commits intoApr 21, 2026
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When the thread state is exiting, the Linux kernel's ptrace implementation returns EPERM. If this happens we should skip the exiting thread, instead of stopping sampling altogether.
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Anything I can do to help you here? :) Otherwise I also have one or two more fixups in my fork https://github.com/I-Al-Istannen/remoteprocess/commits/master/. I will see which are still relevant and make follow up PRs after this one is merged (or before, if you prefer that) :) |
benfred
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Apr 21, 2026
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thanks for the fix! |
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Thanks! |
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When the thread state is exiting, the Linux kernel's ptrace implementation returns EPERM. If this happens we should skip the exiting thread, instead of stopping sampling altogether.
This reduces the
EPERMerrors in the threading stress test benfred/py-spy#771 (comment) to zero. Over a 24h run in a larger program it still fails sampling withEPERMsometimes, but this seems to be quite an improvement.I do not think we can read the exact kernel condition, so this is now open to a race condition: Maybe we really do not have any permission but the thread dies in the split second between the ptrace error and the
existscall. In that case we continue sampling, even though we could have died with a permission error instead. I do not think this is a big problem. If we really have no permission, it will crash in the next iteration once it tries to sample a living thread again.WDYT?