linux-kernel - Re: [PATCH v3 00/35] Compiler-Based Capability- and Locking-Analysis

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Message-ID: <CANpmjNO2b_3Q56kFLN3fAwxj0=pQo0K4CjwMJ9_gHj4c3bVVsg@mail.gmail.com>
Date: Sat, 20 Sep 2025 12:23:24 +0200
From: Marco Elver <elver@...gle.com>
To: Christoph Hellwig <hch@....de>
Cc: Nathan Chancellor <nathan@...nel.org>, Peter Zijlstra <peterz@...radead.org>, 
	Boqun Feng <boqun.feng@...il.com>, Ingo Molnar <mingo@...nel.org>, Will Deacon <will@...nel.org>, 
	"David S. Miller" <davem@...emloft.net>, Luc Van Oostenryck <luc.vanoostenryck@...il.com>, 
	"Paul E. McKenney" <paulmck@...nel.org>, Alexander Potapenko <glider@...gle.com>, Arnd Bergmann <arnd@...db.de>, 
	Bart Van Assche <bvanassche@....org>, Bill Wendling <morbo@...gle.com>, 
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Subject: Re: [PATCH v3 00/35] Compiler-Based Capability- and Locking-Analysis

On Fri, 19 Sept 2025 at 16:08, Christoph Hellwig <hch@....de> wrote:
>
> On Thu, Sep 18, 2025 at 10:45:55AM -0700, Nathan Chancellor wrote:
> > On Thu, Sep 18, 2025 at 04:15:11PM +0200, Christoph Hellwig wrote:
> > > On Thu, Sep 18, 2025 at 03:59:11PM +0200, Marco Elver wrote:
> > > > A Clang version that supports `-Wthread-safety-pointer` and the new
> > > > alias-analysis of capability pointers is required (from this version
> > > > onwards):
> > > >
> > > >   https://github.com/llvm/llvm-project/commit/b4c98fcbe1504841203e610c351a3227f36c92a4 [3]
> > >
> > > There's no chance to make say x86 pre-built binaries for that available?
> >
> > I can use my existing kernel.org LLVM [1] build infrastructure to
> > generate prebuilt x86 binaries. Just give me a bit to build and upload
> > them. You may not be the only developer or maintainer who may want to
> > play with this.
>
> That did work, thanks.
>
> I started to play around with that.  For the nvme code adding the
> annotations was very simply, and I also started adding trivial
> __guarded_by which instantly found issues.
>
> For XFS it was a lot more work and I still see tons of compiler
> warnings, which I'm not entirely sure how to address.  Right now I
> see three major classes:
>
> 1) locks held over loop iterations like:
>
> fs/xfs/xfs_extent_busy.c:573:26: warning: expecting spinlock 'xfs_group_hold(busyp->group)..xg_busy_extents->eb_lock' to be held at start of each loop [-Wthread-safety-analysis]
>   573 |                 struct xfs_group        *xg = xfs_group_hold(busyp->group);
>       |                                               ^
> fs/xfs/xfs_extent_busy.c:577:3: note: spinlock acquired here
>   577 |                 spin_lock(&eb->eb_lock);
>       |                 ^
>
> This is perfectly find code and needs some annotations, but I can't find
> any good example.

This is an interesting one, and might be a bug in the alias analysis I
recently implemented in Clang. I'll try to figure out a fix.