Re: GRUB bug with Btrfs multiple devices

From: Goffredo Baroncelli <kreijack@libero.it>
To: Chris Murphy <lists@colorremedies.com>,
	Btrfs BTRFS <linux-btrfs@vger.kernel.org>
Subject: Re: GRUB bug with Btrfs multiple devices
Date: Tue, 26 Nov 2019 22:11:23 +0100	[thread overview]
Message-ID: <a48a6c50-3a03-0420-ad8c-f589fafe6035@libero.it> (raw)
In-Reply-To: <CAJCQCtSeZu8fRzjABXh3wxvBDEajGutAU4LWu0RcJv-6pd+RGQ@mail.gmail.com>

On 26/11/2019 05.05, Chris Murphy wrote:
> grub2-efi-x64-2.02-100.fc31.x86_64
> kernel-5.3.13-300.fc31.x86_64
> 
> I've seen this before, so it isn't a regression in either of the above
> versions. But I'm also not certain when the regression occurred,
> because the last time I tested Btrfs multiple devices (specifically
> data single profile), was years ago and I didn't run into this.

 From the video, it seems that GRUB complaints about a "failure reading". However GRUB is capable to perform the boot and because the profiles are "single (no redundancy), it seems a "false positive" error.

When I added the RADID5/6 support to grub, I remember errors like what you showed. However it happened 1 year ago, so my remember may be wrong.
I noticed that GRUB test a lot of disks (hd0 ... hd3) . Could you be so kindly to share the disks layout ? Most error is something like "failure reading sector 0xXX". However I can't read the XX number: could you be so kindly to tell us which number is "XX" ? It seems 0x80... but my eyes are bad and your video is even worse :-)

I think that the errors is due to the "rescan" logic (see grub commit [1]). Could you try a more recent grub (2.04 instead of 2.02) ?

> The gist to reproduce:
> 1. btrfs single device, single profile data, single profile metadata
> 2. device starts to run out of space; no problem 'btrfs device add
> /dev/'  voila it works, reboots, keeps on working for a while, but
> then...
> 3. install a kernel or two or three or four
> 
> I suspect that at some point kernels end up on the newly added device
> due to new block groups eventually being created there, and GRUB
> subsequently gets confused, starts spewing a bunch of error
> information which I have to page through. Eventually it does find
> everything and does boot. But it's kinda ugly and I'm not really sure
> how to gather more information.
> 
> Shaky cam video of the boot is here:
> https://photos.app.goo.gl/wvJbB6kBEFzNwogo6
> 
> 

[1] http://git.savannah.gnu.org/cgit/grub.git/commit/grub-core/fs/btrfs.c?id=fd5a1d82f1d6a0482f5fe201ce646ddba8574bab

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