linux-kernel - Re: Circular lock dep in btrfs triggered by shrinker

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Message-ID: <CAOesGMgjfpifo4xWaiT5KGx1_knOkqgGAb5+dTVbh+6S41Smag@mail.gmail.com>
Date:   Tue, 23 Oct 2018 09:41:40 +0100
From:   Olof Johansson <olof@...om.net>
To:     dsterba@...e.cz, dsterba@...e.de, linux-btrfs@...r.kernel.org,
        Chris Mason <clm@...com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Circular lock dep in btrfs triggered by shrinker

On Mon, Oct 22, 2018 at 7:22 PM David Sterba <dsterba@...e.cz> wrote:
>
> On Mon, Oct 22, 2018 at 03:07:26AM -0700, Olof Johansson wrote:
> > I hit the below circular locking dependency. Seems like the assumption made in
> > 712e36c5f2a7fa56 ("btrfs: use GFP_KERNEL in btrfs_alloc_inode") either isn't
> > true, or has since changed?
>
> I think it must have been there from the beginning. There were reports
> of this lockdep warning like the below and IIRC a few more
> (https://lkml.kernel.org/r/20180627120523.GA2287@suse.cz), but without a
> resolution.
>
> Incidentally, there was a fix that's now in the 4.20 pull and only after
> I had seen your report I realized that it was the fix for the warning:
>
> https://git.kernel.org/pub/scm/linux/kernel/git/kdave/linux.git/commit/?h=for-4.20-part1&id=84de76a2fb217dc1b6bc2965cc397d1648aa1404
>
> It disables the filesystem allocations using the memalloc_nofs mechanism
> around free space inode allocation, while my original patch expected
> only regular inodes created by VFS.

Ah, great. I'll take that branch for a spin later today and confirm at
my end too.


-Olof