[PATCH v2 0/1] fs/writeback: skip AS_NO_DATA_INTEGRITY mappings in wait_sb_inodes()

[PATCH v2 0/1] fs/writeback: skip AS_NO_DATA_INTEGRITY mappings in wait_sb_inodes()

[Joanne Koong]

This patch reverts fuse back to its original behavior of sync being a no-op.

This fixes the userspace regression reported by Athul and J. upstream in
[1][2] where if there is a bug in a fuse server that causes the server to
never complete writeback, it will make wait_sb_inodes() wait forever.

Thanks,
Joanne

[1] https://lore.kernel.org/regressions/CAJnrk1ZjQ8W8NzojsvJPRXiv9TuYPNdj8Ye7=Cgkj=iV_i8EaA@mail.gmail.com/T/#t
[2] https://lore.kernel.org/linux-fsdevel/aT7JRqhUvZvfUQlV@eldamar.lan/

Changelog:
v1: https://lore.kernel.org/linux-mm/20251120184211.2379439-1-joannelkoong@gmail.com/
* Change AS_WRITEBACK_MAY_HANG to AS_NO_DATA_INTEGRITY and keep
  AS_WRITEBACK_MAY_DEADLOCK_ON_RECLAIM as is.

Joanne Koong (1):
  fs/writeback: skip AS_NO_DATA_INTEGRITY mappings in wait_sb_inodes()

 fs/fs-writeback.c       |  3 ++-
 fs/fuse/file.c          |  4 +++-
 include/linux/pagemap.h | 11 +++++++++++
 3 files changed, 16 insertions(+), 2 deletions(-)

-- 
2.47.3

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

[Joanne Koong]

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);
+	}
 
 	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;
-- 
2.47.3

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

[Bernd Schubert]

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?

>   
>   	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>

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

[Joanne Koong]

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>

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

[J. Neuschäfer]

On Sun, Dec 14, 2025 at 07:00:43PM -0800, 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>

I can confirm that this patch fixes the issue I reported.
(Tested by applying it on top of v6.19-rc1)

Tested-by: J. Neuschäfer <j.neuschaefer@gmx.net>

Thank you very much!


> ---
>  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);
> +	}
>  
>  	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;
> -- 
> 2.47.3
>