linux-kernel - Re: lockdep trace with xfs + mm in it from 5.7.0-rc5

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Message-ID: <20200522204308.GC8230@magnolia>
Date:   Fri, 22 May 2020 13:43:08 -0700
From:   "Darrick J. Wong" <darrick.wong@...cle.com>
To:     Dave Chinner <david@...morbit.com>
Cc:     Dave Airlie <airlied@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        xfs <linux-xfs@...r.kernel.org>
Subject: Re: lockdep trace with xfs + mm in it from 5.7.0-rc5

On Fri, May 22, 2020 at 10:30:27AM +1000, Dave Chinner wrote:
> On Thu, May 21, 2020 at 04:13:12PM -0700, Darrick J. Wong wrote:
> > [cc linux-xfs]
> > 
> > On Fri, May 22, 2020 at 08:21:50AM +1000, Dave Airlie wrote:
> > > Hi,
> > > 
> > > Just updated a rawhide VM to the Fedora 5.7.0-rc5 kernel, did some
> > > package building,
> > > 
> > > got the below trace, not sure if it's known and fixed or unknown.
> > 
> > It's a known false-positive.  An inode can't simultaneously be getting
> > reclaimed due to zero refcount /and/ be the target of a getxattr call.
> > Unfortunately, lockdep can't tell the difference, and it seems a little
> > strange to set NOFS on the allocation (which increases the chances of a
> > runtime error) just to quiet that down.
> 
> __GFP_NOLOCKDEP is the intended flag to telling memory allocation
> that lockdep is stupid.
> 
> However, it seems that the patches that were in progress some months
> ago to convert XFS to kmalloc interfaces and using GFP flags
> directly stalled - being able to mark locations like this with
> __GFP_NOLOCKDEP was one of the main reasons for getting rid of all
> the internal XFS memory allocation wrappers...

Question is, should I spend time adding a GFP_NOLOCKDEP bandaid to XFS
or would my time be better spent reviewing your async inode reclaim
series to make this go away for real?

(Dang, now that I phrase it that way, Imma go read that series.)

--D

> Cheers,
> 
> Dave.
> -- 
> Dave Chinner
> david@...morbit.com