Comment 59 for bug 1796292

On Thu, Aug 1, 2019 at 10:15 AM Andrea Righi <email address hidden>
wrote:

> Thanks Ryan, this is very interesting:
>
> [ 259.411486] bcache: register_bcache() error /dev/vdg: device already
> registered (emitting change event)
> [ 259.537070] bcache: register_bcache() error /dev/vdg: device already
> registered (emitting change event)
> [ 259.797830] bcache: register_bcache() error /dev/vdg: device already
> registered (emitting change event)
> [ 259.900392] bcache: register_bcache() error /dev/vdg: device already
> registered (emitting change event)
>
> It looks that we're trying to register /dev/vdg multiple times as a
> backing device (make-bcache -B). I'm not getting this message during my
> tests, so that might be required to reproduce that particular deadlock.
>

We carry a specific sauce patch to ensure that if the cacheset is already
online, and a backing device
shows up later, that the kernel emits the change event to trigger the udev
rules to generate the
symlink for /dev/bcache/by-uuid. I don't think the patch we carry is at
issue since we are just detecting
the re-register scenario and emitting a change uevent;

https://www.spinics.net/lists/linux-bcache/msg05833.html

We may want to resubmit that now to see if they'll take that or even want
to deal with the scenario
in a cleaner way;

>
> I'll modify my test case to trigger these errors and see if I can
> reproduce the hung task timeout issue.
>

I can provide you a setup to reproduce this. I'll put together a doc.

> --
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> report.
> https://bugs.launchpad.net/bugs/1796292
>
> Title:
> Tight timeout for bcache removal causes spurious failures
>
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