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

Marco Elver
2025-09-20T12:45:29Z

On Sat, 20 Sept 2025 at 12:23, Marco Elver <elver@google.com> wrote:
>
> On Fri, 19 Sept 2025 at 16:08, Christoph Hellwig <hch@lst.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.

This fixes the problem: https://github.com/llvm/llvm-project/pull/159921

I guess I have to update the base Clang commit hash for v4 again. :-)

And thanks for testing!