Re: [PATCH v2 1/1] fs/writeback: skip AS_NO_DATA_INTEGRITY mappings in wait_sb_inodes()

[Joanne Koong <joannelkoong@gmail.com>]

On Tue, Dec 16, 2025 at 1:09 AM Bernd Schubert <bernd@bsbernd.com> wrote:
>
> On 12/15/25 04:00, Joanne Koong wrote:
> > Skip waiting on writeback for inodes that belong to mappings that do not
> > have data integrity guarantees (denoted by the AS_NO_DATA_INTEGRITY
> > mapping flag).
> >
> > This restores fuse back to prior behavior where syncs are no-ops. This
> > is needed because otherwise, if a system is running a faulty fuse
> > server that does not reply to issued write requests, this will cause
> > wait_sb_inodes() to wait forever.
> >
> > Fixes: 0c58a97f919c ("fuse: remove tmp folio for writebacks and internal rb tree")
> > Reported-by: Athul Krishna <athul.krishna.kr@protonmail.com>
> > Reported-by: J. Neuschäfer <j.neuschaefer@gmx.net>
> > Cc: stable@vger.kernel.org
> > Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
> > ---
> >   fs/fs-writeback.c       |  3 ++-
> >   fs/fuse/file.c          |  4 +++-
> >   include/linux/pagemap.h | 11 +++++++++++
> >   3 files changed, 16 insertions(+), 2 deletions(-)
> >
> > diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
> > index 6800886c4d10..ab2e279ed3c2 100644
> > --- a/fs/fs-writeback.c
> > +++ b/fs/fs-writeback.c
> > @@ -2751,7 +2751,8 @@ static void wait_sb_inodes(struct super_block *sb)
> >                * do not have the mapping lock. Skip it here, wb completion
> >                * will remove it.
> >                */
> > -             if (!mapping_tagged(mapping, PAGECACHE_TAG_WRITEBACK))
> > +             if (!mapping_tagged(mapping, PAGECACHE_TAG_WRITEBACK) ||
> > +                 mapping_no_data_integrity(mapping))
> >                       continue;
> >
> >               spin_unlock_irq(&sb->s_inode_wblist_lock);
> > diff --git a/fs/fuse/file.c b/fs/fuse/file.c
> > index 01bc894e9c2b..3b2a171e652f 100644
> > --- a/fs/fuse/file.c
> > +++ b/fs/fuse/file.c
> > @@ -3200,8 +3200,10 @@ void fuse_init_file_inode(struct inode *inode, unsigned int flags)
> >
> >       inode->i_fop = &fuse_file_operations;
> >       inode->i_data.a_ops = &fuse_file_aops;
> > -     if (fc->writeback_cache)
> > +     if (fc->writeback_cache) {
> >               mapping_set_writeback_may_deadlock_on_reclaim(&inode->i_data);
> > +             mapping_set_no_data_integrity(&inode->i_data);
> > +     }
>
> For a future commit, maybe we could add a FUSE_INIT flag that allows privileged
> fuse server to not set this? Maybe even in combination with an enforced request
> timeout?

That sounds good, thanks for reviewing this, Bernd!

>
> >
> >       INIT_LIST_HEAD(&fi->write_files);
> >       INIT_LIST_HEAD(&fi->queued_writes);
> > diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
> > index 31a848485ad9..ec442af3f886 100644
> > --- a/include/linux/pagemap.h
> > +++ b/include/linux/pagemap.h
> > @@ -210,6 +210,7 @@ enum mapping_flags {
> >       AS_WRITEBACK_MAY_DEADLOCK_ON_RECLAIM = 9,
> >       AS_KERNEL_FILE = 10,    /* mapping for a fake kernel file that shouldn't
> >                                  account usage to user cgroups */
> > +     AS_NO_DATA_INTEGRITY = 11, /* no data integrity guarantees */
> >       /* Bits 16-25 are used for FOLIO_ORDER */
> >       AS_FOLIO_ORDER_BITS = 5,
> >       AS_FOLIO_ORDER_MIN = 16,
> > @@ -345,6 +346,16 @@ static inline bool mapping_writeback_may_deadlock_on_reclaim(const struct addres
> >       return test_bit(AS_WRITEBACK_MAY_DEADLOCK_ON_RECLAIM, &mapping->flags);
> >   }
> >
> > +static inline void mapping_set_no_data_integrity(struct address_space *mapping)
> > +{
> > +     set_bit(AS_NO_DATA_INTEGRITY, &mapping->flags);
> > +}
> > +
> > +static inline bool mapping_no_data_integrity(const struct address_space *mapping)
> > +{
> > +     return test_bit(AS_NO_DATA_INTEGRITY, &mapping->flags);
> > +}
> > +
> >   static inline gfp_t mapping_gfp_mask(const struct address_space *mapping)
> >   {
> >       return mapping->gfp_mask;
>
>
> Reviewed-by: Bernd Schubert <bschubert@ddn.com>