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fix: storage_flush check thread exists before joining #554

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fix: storage_flush check thread exists before joining #554

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5 changes: 3 additions & 2 deletions mtda/storage/writer.py
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Original file line number Diff line number Diff line change
Expand Up @@ -93,8 +93,9 @@ def flush(self, size):
self._receiving = False
self._size = size

self.mtda.debug(2, "storage.writer.flush(): waiting on thread...")
self._thread.join()
if self._thread is not None:
self.mtda.debug(2, "storage.writer.flush(): waiting on thread...")
self._thread.join()
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@fmoessbauer fmoessbauer Dec 16, 2025

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This just shortens the windows of the race condition, right?

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@shikl3x7 shikl3x7 Dec 16, 2025

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Yes, this should shorten and also ensure

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@fmoessbauer fmoessbauer Dec 16, 2025

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Why ensure? We still have a TOCTOU issue here if I understand the underlying problem correctly. How can it be, that the self._thread object does not exist anymore?

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@shikl3x7 shikl3x7 Dec 17, 2025 •
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Issue that we observed did not have consistent reproducibility, whenever we tried the storage write as bellow, we used to get the error, but not always.

gourav@gourav:~/images/lx1/example$ mtda-cli -r 134.86.254.94 storage write isar-image-installer-lx1-x86-uefi.wic
Discovered bmap file 'isar-image-installer-lx1-x86-uefi.wic.bmap'
isar-image-installer-lx1-x86-uefi.wic: [####################] 100% (650 MiB read, 5.70 GiB written, 36 KiB/s)

'storage write' failed! ('NoneType' object has no attribute 'join')

And the issue was intermittent and no corruption on the image was observed.

I had seen the stop method, saw that it uses similar logic to ensure the thread is not none and then join.
So, I used the term ensure. And shortens because it also reduces the time window if join method are called simultaneously.

I am not sure if this is a TOCTOU issue, because we have the while loop which makes sure the writing is complete, so thread is not under usage, so at the moment I have some suspects that, somewhere stop is being called, because only that has capability to set to none type, but not sure of why or how.

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@fmoessbauer fmoessbauer Dec 17, 2025

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I have some suspects that, somewhere stop is being called, because only that has capability to set to none type, but not sure of why or how.

You could print a traceback whenever stop is called to debug this. Anyways, I approved the MR as it solves the issue for us. Once the root cause is found, we still can revert the patch.

result = not self._failed

self.mtda.debug(3, f"storage.writer.flush(): {result}")
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