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From: Eric Ren <renzhengeek@gmail.com>
Date: Sun, 14 Apr 2019 15:30:19 +0800
Message-ID: <CAKM4Aew4cNU0_8mBYCXjxPOzDMUt8eGtJP5mjq3g3vUUPw6-rA@mail.gmail.com>
Subject: Re: [linux-lvm] lvcreate hangs forever and udev work timeout
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To: Zdenek Kabelac <zkabelac@redhat.com>
Cc: LVM2 development <lvm-devel@redhat.com>, LVM general discussion and development <linux-lvm@redhat.com>

Hi,

The reason is found out, as you've predicted.

> is it because of slow read operation (i.e. some raid arrays are known to
> wake-up slowly)

The udev worker is blocked until timeout before killed, cause the
"blkid" in /usr/lib/udev/rules.d/13-dm-disk.rules is too slow because
of high IO load on the thin pool.

After remove this rule:

IMPORT{builtin}="blkid"

for testing, the problem cannot be reproduced any more.

But, we tried to increate udevd timeout to 5 min, the problem still
happens; with 10 min timeout, can workaround this problem.

>From my understanding, the blkid will only read the fs superblock, why
it takes so long for a small IO to finish, even under high IO load?

Regards,
Eric