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bcache causes "waiting for uevents to be processed" issue
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pigsboss
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Joined: 27 Dec 2011
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PostPosted: Fri Jan 15, 2016 3:14 am    Post subject: bcache causes "waiting for uevents to be processed" Reply with quote

I've been using bcache on my laptop for years and everything was fine until I tried to setup bcache powered working directory on my desktop (Gentoo Linux, latest stable kernel, openrc, udev-225).

Layout
Cache device: LSI Megaraid 9270-8i configured RAID0 (SSD 256GB x 6, writeback), identified as /dev/sda.
Block device: mdadm configured RAID5 (HDD 3TB x 4), identified as /dev/md0.

bcache setup
Code:

make-bcache -C /dev/sda -B /dev/md0
echo "writeback" > /sys/block/bcache0/bcache/cache_mode
mkfs.ext4 -L data /dev/bcache0


IO performance
Sequential read: 1800MB/s
Sequential write: 2900MB/s
4K random IO: 2MB/s

It could be cool if it ends here.
However, after I reboot the system, it will definitely hang at "waiting for uevents to be processed" for about one minute, and the configured bcache device will be gone for sure. I can't find it in /dev/ or /sys/block/ any more. The dmesg shows /dev/sda has been registered as cache device and /dev/md0 has been registered as block device though. I can't attach them since /sys/block/bcache0 is gone. If I wipefs both devices, and reset the machine, however, the next boot is normal, where "waiting for uevents to be processed" is passed in a few seconds as expected.

I can reproduce this so this issue is not probabilistic.

How can I provide more detailed info? I've set udev_log="debug" but there is still not much info about bcache in dmesg.
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pigsboss
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Joined: 27 Dec 2011
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PostPosted: Thu Jan 21, 2016 1:28 pm    Post subject: Reply with quote

Gave up working on bcache.
Now I'm using lvmcache and I'm very happy so far.
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