Re: next-20250721 arm64 16K and 64K page size WARNING fs fuse file.c at fuse_iomap_writeback_range

[Joanne Koong <joannelkoong@gmail.com>]

On Wed, Jul 23, 2025 at 11:42 AM Joanne Koong <joannelkoong@gmail.com> wrote:
>
> On Wed, Jul 23, 2025 at 7:46 AM Darrick J. Wong <djwong@kernel.org> wrote:
> >
> > [cc Joanne]
> >
> > On Wed, Jul 23, 2025 at 05:14:28PM +0530, Naresh Kamboju wrote:
> > > Regressions found while running LTP msync04 tests on qemu-arm64 running
> > > Linux next-20250721, next-20250722 and next-20250723 with 16K and 64K
> > > page size enabled builds.
> > >
> > > CONFIG_ARM64_64K_PAGES=y ( kernel warning as below )
> > > CONFIG_ARM64_16K_PAGES=y ( kernel warning as below )
> > >
> > > No warning noticed with 4K page size.
> > > CONFIG_ARM64_4K_PAGES=y works as expected
> >
> > You might want to cc Joanne since she's been working on large folio
> > support in fuse.
> >
> > > First seen on the tag next-20250721.
> > > Good: next-20250718
> > > Bad:  next-20250721 to next-20250723
>
> Thanks for the report. Is there a link to the script that mounts the
> fuse server for these tests? I'm curious whether this was mounted as a
> fuseblk filesystem.
>
> > >
> > > Regression Analysis:
> > > - New regression? Yes
> > > - Reproducibility? Yes
> > >
> > > Test regression: next-20250721 arm64 16K and 64K page size WARNING fs
> > > fuse file.c at fuse_iomap_writeback_range
> > >
> > > Reported-by: Linux Kernel Functional Testing <lkft@linaro.org>
> > >
> > > ## Test log
> > > ------------[ cut here ]------------
> > > [  343.828105] WARNING: fs/fuse/file.c:2146 at
> > > fuse_iomap_writeback_range+0x478/0x558 [fuse], CPU#0: msync04/4190
> >
> >         WARN_ON_ONCE(len & (PAGE_SIZE - 1));
> >
> > /me speculates that this might be triggered by an attempt to write back
> > some 4k fsblock within a 16/64k base page?
> >
>
> I think this can happen on 4k base pages as well actually. On the
> iomap side, the length passed is always block-aligned and in fuse, we
> set blkbits to be PAGE_SHIFT so theoretically block-aligned is always
> page-aligned, but I missed that if it's a "fuseblk" filesystem, that
> isn't true and the blocksize is initialized to a default size of 512
> or whatever block size is passed in when it's mounted.
>
> I'll send out a patch to remove this line. It doesn't make any
> difference for fuse_iomap_writeback_range() logic whether len is
> page-aligned or not; I had added it as a sanity-check against sketchy
> ranges.
>

https://lore.kernel.org/linux-fsdevel/20250723230850.2395561-1-joannelkoong@gmail.com/T/#u
is the patch for removing this