Bug 275570
| Summary: | self-referential nullfs mount over tmpfs in combination with MNT_UPDATE results in a hang | ||||||
|---|---|---|---|---|---|---|---|
| Product: | Base System | Reporter: | Alex S <iwtcex> | ||||
| Component: | kern | Assignee: | freebsd-fs (Nobody) <fs> | ||||
| Status: | New --- | ||||||
| Severity: | Affects Only Me | CC: | arrowd, dfr, kevans, pho | ||||
| Priority: | --- | ||||||
| Version: | 14.0-RELEASE | ||||||
| Hardware: | Any | ||||||
| OS: | Any | ||||||
| Attachments: |
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Let's start with dfr@, since the sample in question is specifically null-mounting a file over itself.
With the deadlock.c attached, I hit it best with a stupid simple loop:
```
#!/bin/sh
iteration=1
while true; do
echo "Iteration $iteration"
./a.out
iteration=$((iteration + 1))
done
```
Took me about 15 tries. When it deadlocks on my machine, it's in the nmount(2) that would be null-mounting the file over itself rather than the follow-up MNT_UPDATE of the tmpfs mount holding it.
Oh, let's CC pho@ too, as this might have some good inspiration for his testing... |
Created attachment 246821 [details] deadlock.c Update the issue title as you see fit. The attached repro works in 14 and CURRENT. I admit mounting a path on itself is a bit silly (and probably should be forbidden), but the hang is still worth a look.