[PATCH] fs: invalidate page cache after end_io() in dio completion

[PATCH] fs: invalidate page cache after end_io() in dio completion

[Eryu Guan]

Commit 332391a9935d ("fs: Fix page cache inconsistency when mixing
buffered and AIO DIO") moved page cache invalidation from
iomap_dio_rw() to iomap_dio_complete() for iomap based direct write
path, but before the dio->end_io() call, and it re-introdued the bug
fixed by commit c771c14baa33 ("iomap: invalidate page caches should
be after iomap_dio_complete() in direct write").

I found this because fstests generic/418 started failing on XFS with
v4.14-rc3 kernel, which is the regression test for this specific
bug.

So similarly, fix it by moving dio->end_io() (which does the
unwritten extent conversion) before page cache invalidation, to make
sure next buffer read reads the final real allocations not unwritten
extents. I also add some comments about why should end_io() go first
in case we get it wrong again in the future.

Note that, there's no such problem in the non-iomap based direct
write path, because we didn't remove the page cache invalidation
after the ->direct_IO() in generic_file_direct_write() call, but I
decided to fix dio_complete() too so we don't leave a landmine
there, also be consistent with iomap_dio_complete().

Fixes: 332391a9935d ("fs: Fix page cache inconsistency when mixing buffered and AIO DIO")
Signed-off-by: Eryu Guan <eguan@redhat.com>
---
 fs/direct-io.c | 20 ++++++++++++--------
 fs/iomap.c     | 41 ++++++++++++++++++++++++-----------------
 2 files changed, 36 insertions(+), 25 deletions(-)

diff --git a/fs/direct-io.c b/fs/direct-io.c
index 62cf812ed0e5..1dba6842c349 100644
--- a/fs/direct-io.c
+++ b/fs/direct-io.c
@@ -259,12 +259,24 @@ static ssize_t dio_complete(struct dio *dio, ssize_t ret, bool is_async)
 	if (ret == 0)
 		ret = transferred;
 
+	if (dio->end_io) {
+		// XXX: ki_pos??
+		err = dio->end_io(dio->iocb, offset, ret, dio->private);
+		if (err)
+			ret = err;
+	}
+
 	/*
 	 * Try again to invalidate clean pages which might have been cached by
 	 * non-direct readahead, or faulted in by get_user_pages() if the source
 	 * of the write was an mmap'ed region of the file we're writing.  Either
 	 * one is a pretty crazy thing to do, so we don't support it 100%.  If
 	 * this invalidation fails, tough, the write still worked...
+	 *
+	 * And this page cache invalidation has to be after dio->end_io(), as
+	 * some filesystems convert unwritten extents to real allocations in
+	 * end_io() when necessary, otherwise a racing buffer read would cache
+	 * zeros from unwritten extents.
 	 */
 	if (ret > 0 && dio->op == REQ_OP_WRITE &&
 	    dio->inode->i_mapping->nrpages) {
@@ -274,14 +286,6 @@ static ssize_t dio_complete(struct dio *dio, ssize_t ret, bool is_async)
 		WARN_ON_ONCE(err);
 	}
 
-	if (dio->end_io) {
-
-		// XXX: ki_pos??
-		err = dio->end_io(dio->iocb, offset, ret, dio->private);
-		if (err)
-			ret = err;
-	}
-
 	if (!(dio->flags & DIO_SKIP_DIO_COUNT))
 		inode_dio_end(dio->inode);
 
diff --git a/fs/iomap.c b/fs/iomap.c
index be61cf742b5e..d4801f8dd4fd 100644
--- a/fs/iomap.c
+++ b/fs/iomap.c
@@ -714,23 +714,9 @@ static ssize_t iomap_dio_complete(struct iomap_dio *dio)
 {
 	struct kiocb *iocb = dio->iocb;
 	struct inode *inode = file_inode(iocb->ki_filp);
+	loff_t offset = iocb->ki_pos;
 	ssize_t ret;
 
-	/*
-	 * Try again to invalidate clean pages which might have been cached by
-	 * non-direct readahead, or faulted in by get_user_pages() if the source
-	 * of the write was an mmap'ed region of the file we're writing.  Either
-	 * one is a pretty crazy thing to do, so we don't support it 100%.  If
-	 * this invalidation fails, tough, the write still worked...
-	 */
-	if (!dio->error &&
-	    (dio->flags & IOMAP_DIO_WRITE) && inode->i_mapping->nrpages) {
-		ret = invalidate_inode_pages2_range(inode->i_mapping,
-				iocb->ki_pos >> PAGE_SHIFT,
-				(iocb->ki_pos + dio->size - 1) >> PAGE_SHIFT);
-		WARN_ON_ONCE(ret);
-	}
-
 	if (dio->end_io) {
 		ret = dio->end_io(iocb,
 				dio->error ? dio->error : dio->size,
@@ -742,12 +728,33 @@ static ssize_t iomap_dio_complete(struct iomap_dio *dio)
 	if (likely(!ret)) {
 		ret = dio->size;
 		/* check for short read */
-		if (iocb->ki_pos + ret > dio->i_size &&
+		if (offset + ret > dio->i_size &&
 		    !(dio->flags & IOMAP_DIO_WRITE))
-			ret = dio->i_size - iocb->ki_pos;
+			ret = dio->i_size - offset;
 		iocb->ki_pos += ret;
 	}
 
+	/*
+	 * Try again to invalidate clean pages which might have been cached by
+	 * non-direct readahead, or faulted in by get_user_pages() if the source
+	 * of the write was an mmap'ed region of the file we're writing.  Either
+	 * one is a pretty crazy thing to do, so we don't support it 100%.  If
+	 * this invalidation fails, tough, the write still worked...
+	 *
+	 * And this page cache invalidation has to be after dio->end_io(), as
+	 * some filesystems convert unwritten extents to real allocations in
+	 * end_io() when necessary, otherwise a racing buffer read would cache
+	 * zeros from unwritten extents.
+	 */
+	if (!dio->error &&
+	    (dio->flags & IOMAP_DIO_WRITE) && inode->i_mapping->nrpages) {
+		int err;
+		err = invalidate_inode_pages2_range(inode->i_mapping,
+				offset >> PAGE_SHIFT,
+				(offset + dio->size - 1) >> PAGE_SHIFT);
+		WARN_ON_ONCE(err);
+	}
+
 	inode_dio_end(file_inode(iocb->ki_filp));
 	kfree(dio);
 
-- 
2.13.6

Re: [PATCH] fs: invalidate page cache after end_io() in dio completion

[Eryu Guan]

On Wed, Oct 04, 2017 at 12:02:01AM +0800, Eryu Guan wrote:
> Commit 332391a9935d ("fs: Fix page cache inconsistency when mixing
> buffered and AIO DIO") moved page cache invalidation from
> iomap_dio_rw() to iomap_dio_complete() for iomap based direct write
> path, but before the dio->end_io() call, and it re-introdued the bug
> fixed by commit c771c14baa33 ("iomap: invalidate page caches should
> be after iomap_dio_complete() in direct write").
> 
> I found this because fstests generic/418 started failing on XFS with
> v4.14-rc3 kernel, which is the regression test for this specific
> bug.
> 
> So similarly, fix it by moving dio->end_io() (which does the
> unwritten extent conversion) before page cache invalidation, to make
> sure next buffer read reads the final real allocations not unwritten
> extents. I also add some comments about why should end_io() go first
> in case we get it wrong again in the future.
> 
> Note that, there's no such problem in the non-iomap based direct
> write path, because we didn't remove the page cache invalidation
> after the ->direct_IO() in generic_file_direct_write() call, but I
> decided to fix dio_complete() too so we don't leave a landmine
> there, also be consistent with iomap_dio_complete().
> 
> Fixes: 332391a9935d ("fs: Fix page cache inconsistency when mixing buffered and AIO DIO")
> Signed-off-by: Eryu Guan <eguan@redhat.com>

Ping on this patch, and cc Jan for broader attention.

It fixed a regression (re-)introduced in v4.14-rc3, and currently only
XFS was affected (because of the iomap based DIO adoption). I've tested
it with the reproducer generic/418, LTP and full rounds of fstests runs
with different feature and block size enabled.

Thanks,
Eryu

> ---
>  fs/direct-io.c | 20 ++++++++++++--------
>  fs/iomap.c     | 41 ++++++++++++++++++++++++-----------------
>  2 files changed, 36 insertions(+), 25 deletions(-)
> 
> diff --git a/fs/direct-io.c b/fs/direct-io.c
> index 62cf812ed0e5..1dba6842c349 100644
> --- a/fs/direct-io.c
> +++ b/fs/direct-io.c
> @@ -259,12 +259,24 @@ static ssize_t dio_complete(struct dio *dio, ssize_t ret, bool is_async)
>  	if (ret == 0)
>  		ret = transferred;
>  
> +	if (dio->end_io) {
> +		// XXX: ki_pos??
> +		err = dio->end_io(dio->iocb, offset, ret, dio->private);
> +		if (err)
> +			ret = err;
> +	}
> +
>  	/*
>  	 * Try again to invalidate clean pages which might have been cached by
>  	 * non-direct readahead, or faulted in by get_user_pages() if the source
>  	 * of the write was an mmap'ed region of the file we're writing.  Either
>  	 * one is a pretty crazy thing to do, so we don't support it 100%.  If
>  	 * this invalidation fails, tough, the write still worked...
> +	 *
> +	 * And this page cache invalidation has to be after dio->end_io(), as
> +	 * some filesystems convert unwritten extents to real allocations in
> +	 * end_io() when necessary, otherwise a racing buffer read would cache
> +	 * zeros from unwritten extents.
>  	 */
>  	if (ret > 0 && dio->op == REQ_OP_WRITE &&
>  	    dio->inode->i_mapping->nrpages) {
> @@ -274,14 +286,6 @@ static ssize_t dio_complete(struct dio *dio, ssize_t ret, bool is_async)
>  		WARN_ON_ONCE(err);
>  	}
>  
> -	if (dio->end_io) {
> -
> -		// XXX: ki_pos??
> -		err = dio->end_io(dio->iocb, offset, ret, dio->private);
> -		if (err)
> -			ret = err;
> -	}
> -
>  	if (!(dio->flags & DIO_SKIP_DIO_COUNT))
>  		inode_dio_end(dio->inode);
>  
> diff --git a/fs/iomap.c b/fs/iomap.c
> index be61cf742b5e..d4801f8dd4fd 100644
> --- a/fs/iomap.c
> +++ b/fs/iomap.c
> @@ -714,23 +714,9 @@ static ssize_t iomap_dio_complete(struct iomap_dio *dio)
>  {
>  	struct kiocb *iocb = dio->iocb;
>  	struct inode *inode = file_inode(iocb->ki_filp);
> +	loff_t offset = iocb->ki_pos;
>  	ssize_t ret;
>  
> -	/*
> -	 * Try again to invalidate clean pages which might have been cached by
> -	 * non-direct readahead, or faulted in by get_user_pages() if the source
> -	 * of the write was an mmap'ed region of the file we're writing.  Either
> -	 * one is a pretty crazy thing to do, so we don't support it 100%.  If
> -	 * this invalidation fails, tough, the write still worked...
> -	 */
> -	if (!dio->error &&
> -	    (dio->flags & IOMAP_DIO_WRITE) && inode->i_mapping->nrpages) {
> -		ret = invalidate_inode_pages2_range(inode->i_mapping,
> -				iocb->ki_pos >> PAGE_SHIFT,
> -				(iocb->ki_pos + dio->size - 1) >> PAGE_SHIFT);
> -		WARN_ON_ONCE(ret);
> -	}
> -
>  	if (dio->end_io) {
>  		ret = dio->end_io(iocb,
>  				dio->error ? dio->error : dio->size,
> @@ -742,12 +728,33 @@ static ssize_t iomap_dio_complete(struct iomap_dio *dio)
>  	if (likely(!ret)) {
>  		ret = dio->size;
>  		/* check for short read */
> -		if (iocb->ki_pos + ret > dio->i_size &&
> +		if (offset + ret > dio->i_size &&
>  		    !(dio->flags & IOMAP_DIO_WRITE))
> -			ret = dio->i_size - iocb->ki_pos;
> +			ret = dio->i_size - offset;
>  		iocb->ki_pos += ret;
>  	}
>  
> +	/*
> +	 * Try again to invalidate clean pages which might have been cached by
> +	 * non-direct readahead, or faulted in by get_user_pages() if the source
> +	 * of the write was an mmap'ed region of the file we're writing.  Either
> +	 * one is a pretty crazy thing to do, so we don't support it 100%.  If
> +	 * this invalidation fails, tough, the write still worked...
> +	 *
> +	 * And this page cache invalidation has to be after dio->end_io(), as
> +	 * some filesystems convert unwritten extents to real allocations in
> +	 * end_io() when necessary, otherwise a racing buffer read would cache
> +	 * zeros from unwritten extents.
> +	 */
> +	if (!dio->error &&
> +	    (dio->flags & IOMAP_DIO_WRITE) && inode->i_mapping->nrpages) {
> +		int err;
> +		err = invalidate_inode_pages2_range(inode->i_mapping,
> +				offset >> PAGE_SHIFT,
> +				(offset + dio->size - 1) >> PAGE_SHIFT);
> +		WARN_ON_ONCE(err);
> +	}
> +
>  	inode_dio_end(file_inode(iocb->ki_filp));
>  	kfree(dio);
>  
> -- 
> 2.13.6
> 

Re: [PATCH] fs: invalidate page cache after end_io() in dio completion

[Jan Kara]

On Mon 16-10-17 19:23:00, Eryu Guan wrote:
> On Wed, Oct 04, 2017 at 12:02:01AM +0800, Eryu Guan wrote:
> > Commit 332391a9935d ("fs: Fix page cache inconsistency when mixing
> > buffered and AIO DIO") moved page cache invalidation from
> > iomap_dio_rw() to iomap_dio_complete() for iomap based direct write
> > path, but before the dio->end_io() call, and it re-introdued the bug
> > fixed by commit c771c14baa33 ("iomap: invalidate page caches should
> > be after iomap_dio_complete() in direct write").
> > 
> > I found this because fstests generic/418 started failing on XFS with
> > v4.14-rc3 kernel, which is the regression test for this specific
> > bug.
> > 
> > So similarly, fix it by moving dio->end_io() (which does the
> > unwritten extent conversion) before page cache invalidation, to make
> > sure next buffer read reads the final real allocations not unwritten
> > extents. I also add some comments about why should end_io() go first
> > in case we get it wrong again in the future.
> > 
> > Note that, there's no such problem in the non-iomap based direct
> > write path, because we didn't remove the page cache invalidation
> > after the ->direct_IO() in generic_file_direct_write() call, but I
> > decided to fix dio_complete() too so we don't leave a landmine
> > there, also be consistent with iomap_dio_complete().
> > 
> > Fixes: 332391a9935d ("fs: Fix page cache inconsistency when mixing buffered and AIO DIO")
> > Signed-off-by: Eryu Guan <eguan@redhat.com>
> 
> Ping on this patch, and cc Jan for broader attention.
> 
> It fixed a regression (re-)introduced in v4.14-rc3, and currently only
> XFS was affected (because of the iomap based DIO adoption). I've tested
> it with the reproducer generic/418, LTP and full rounds of fstests runs
> with different feature and block size enabled.

The patch looks good to me. You can add:

Reviewed-by: Jan Kara <jack@suse.cz>

								Honza

> > ---
> >  fs/direct-io.c | 20 ++++++++++++--------
> >  fs/iomap.c     | 41 ++++++++++++++++++++++++-----------------
> >  2 files changed, 36 insertions(+), 25 deletions(-)
> > 
> > diff --git a/fs/direct-io.c b/fs/direct-io.c
> > index 62cf812ed0e5..1dba6842c349 100644
> > --- a/fs/direct-io.c
> > +++ b/fs/direct-io.c
> > @@ -259,12 +259,24 @@ static ssize_t dio_complete(struct dio *dio, ssize_t ret, bool is_async)
> >  	if (ret == 0)
> >  		ret = transferred;
> >  
> > +	if (dio->end_io) {
> > +		// XXX: ki_pos??
> > +		err = dio->end_io(dio->iocb, offset, ret, dio->private);
> > +		if (err)
> > +			ret = err;
> > +	}
> > +
> >  	/*
> >  	 * Try again to invalidate clean pages which might have been cached by
> >  	 * non-direct readahead, or faulted in by get_user_pages() if the source
> >  	 * of the write was an mmap'ed region of the file we're writing.  Either
> >  	 * one is a pretty crazy thing to do, so we don't support it 100%.  If
> >  	 * this invalidation fails, tough, the write still worked...
> > +	 *
> > +	 * And this page cache invalidation has to be after dio->end_io(), as
> > +	 * some filesystems convert unwritten extents to real allocations in
> > +	 * end_io() when necessary, otherwise a racing buffer read would cache
> > +	 * zeros from unwritten extents.
> >  	 */
> >  	if (ret > 0 && dio->op == REQ_OP_WRITE &&
> >  	    dio->inode->i_mapping->nrpages) {
> > @@ -274,14 +286,6 @@ static ssize_t dio_complete(struct dio *dio, ssize_t ret, bool is_async)
> >  		WARN_ON_ONCE(err);
> >  	}
> >  
> > -	if (dio->end_io) {
> > -
> > -		// XXX: ki_pos??
> > -		err = dio->end_io(dio->iocb, offset, ret, dio->private);
> > -		if (err)
> > -			ret = err;
> > -	}
> > -
> >  	if (!(dio->flags & DIO_SKIP_DIO_COUNT))
> >  		inode_dio_end(dio->inode);
> >  
> > diff --git a/fs/iomap.c b/fs/iomap.c
> > index be61cf742b5e..d4801f8dd4fd 100644
> > --- a/fs/iomap.c
> > +++ b/fs/iomap.c
> > @@ -714,23 +714,9 @@ static ssize_t iomap_dio_complete(struct iomap_dio *dio)
> >  {
> >  	struct kiocb *iocb = dio->iocb;
> >  	struct inode *inode = file_inode(iocb->ki_filp);
> > +	loff_t offset = iocb->ki_pos;
> >  	ssize_t ret;
> >  
> > -	/*
> > -	 * Try again to invalidate clean pages which might have been cached by
> > -	 * non-direct readahead, or faulted in by get_user_pages() if the source
> > -	 * of the write was an mmap'ed region of the file we're writing.  Either
> > -	 * one is a pretty crazy thing to do, so we don't support it 100%.  If
> > -	 * this invalidation fails, tough, the write still worked...
> > -	 */
> > -	if (!dio->error &&
> > -	    (dio->flags & IOMAP_DIO_WRITE) && inode->i_mapping->nrpages) {
> > -		ret = invalidate_inode_pages2_range(inode->i_mapping,
> > -				iocb->ki_pos >> PAGE_SHIFT,
> > -				(iocb->ki_pos + dio->size - 1) >> PAGE_SHIFT);
> > -		WARN_ON_ONCE(ret);
> > -	}
> > -
> >  	if (dio->end_io) {
> >  		ret = dio->end_io(iocb,
> >  				dio->error ? dio->error : dio->size,
> > @@ -742,12 +728,33 @@ static ssize_t iomap_dio_complete(struct iomap_dio *dio)
> >  	if (likely(!ret)) {
> >  		ret = dio->size;
> >  		/* check for short read */
> > -		if (iocb->ki_pos + ret > dio->i_size &&
> > +		if (offset + ret > dio->i_size &&
> >  		    !(dio->flags & IOMAP_DIO_WRITE))
> > -			ret = dio->i_size - iocb->ki_pos;
> > +			ret = dio->i_size - offset;
> >  		iocb->ki_pos += ret;
> >  	}
> >  
> > +	/*
> > +	 * Try again to invalidate clean pages which might have been cached by
> > +	 * non-direct readahead, or faulted in by get_user_pages() if the source
> > +	 * of the write was an mmap'ed region of the file we're writing.  Either
> > +	 * one is a pretty crazy thing to do, so we don't support it 100%.  If
> > +	 * this invalidation fails, tough, the write still worked...
> > +	 *
> > +	 * And this page cache invalidation has to be after dio->end_io(), as
> > +	 * some filesystems convert unwritten extents to real allocations in
> > +	 * end_io() when necessary, otherwise a racing buffer read would cache
> > +	 * zeros from unwritten extents.
> > +	 */
> > +	if (!dio->error &&
> > +	    (dio->flags & IOMAP_DIO_WRITE) && inode->i_mapping->nrpages) {
> > +		int err;
> > +		err = invalidate_inode_pages2_range(inode->i_mapping,
> > +				offset >> PAGE_SHIFT,
> > +				(offset + dio->size - 1) >> PAGE_SHIFT);
> > +		WARN_ON_ONCE(err);
> > +	}
> > +
> >  	inode_dio_end(file_inode(iocb->ki_filp));
> >  	kfree(dio);
> >  
> > -- 
> > 2.13.6
> > 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

Re: [PATCH] fs: invalidate page cache after end_io() in dio completion

[Lukas Czerner]

On Mon, Oct 16, 2017 at 07:23:00PM +0800, Eryu Guan wrote:
> On Wed, Oct 04, 2017 at 12:02:01AM +0800, Eryu Guan wrote:
> > Commit 332391a9935d ("fs: Fix page cache inconsistency when mixing
> > buffered and AIO DIO") moved page cache invalidation from
> > iomap_dio_rw() to iomap_dio_complete() for iomap based direct write
> > path, but before the dio->end_io() call, and it re-introdued the bug
> > fixed by commit c771c14baa33 ("iomap: invalidate page caches should
> > be after iomap_dio_complete() in direct write").
> > 
> > I found this because fstests generic/418 started failing on XFS with
> > v4.14-rc3 kernel, which is the regression test for this specific
> > bug.
> > 
> > So similarly, fix it by moving dio->end_io() (which does the
> > unwritten extent conversion) before page cache invalidation, to make
> > sure next buffer read reads the final real allocations not unwritten
> > extents. I also add some comments about why should end_io() go first
> > in case we get it wrong again in the future.
> > 
> > Note that, there's no such problem in the non-iomap based direct
> > write path, because we didn't remove the page cache invalidation
> > after the ->direct_IO() in generic_file_direct_write() call, but I
> > decided to fix dio_complete() too so we don't leave a landmine
> > there, also be consistent with iomap_dio_complete().
> > 
> > Fixes: 332391a9935d ("fs: Fix page cache inconsistency when mixing buffered and AIO DIO")
> > Signed-off-by: Eryu Guan <eguan@redhat.com>
> 
> Ping on this patch, and cc Jan for broader attention.
> 
> It fixed a regression (re-)introduced in v4.14-rc3, and currently only
> XFS was affected (because of the iomap based DIO adoption). I've tested
> it with the reproducer generic/418, LTP and full rounds of fstests runs
> with different feature and block size enabled.
> 
> Thanks,
> Eryu

Ah, right. I did not notice the problem before. Thanks. The patch looks
good.

Reviewed-by: Lukas Czerner <lczerner@redhat.com>

> 
> > ---
> >  fs/direct-io.c | 20 ++++++++++++--------
> >  fs/iomap.c     | 41 ++++++++++++++++++++++++-----------------
> >  2 files changed, 36 insertions(+), 25 deletions(-)
> > 
> > diff --git a/fs/direct-io.c b/fs/direct-io.c
> > index 62cf812ed0e5..1dba6842c349 100644
> > --- a/fs/direct-io.c
> > +++ b/fs/direct-io.c
> > @@ -259,12 +259,24 @@ static ssize_t dio_complete(struct dio *dio, ssize_t ret, bool is_async)
> >  	if (ret == 0)
> >  		ret = transferred;
> >  
> > +	if (dio->end_io) {
> > +		// XXX: ki_pos??
> > +		err = dio->end_io(dio->iocb, offset, ret, dio->private);
> > +		if (err)
> > +			ret = err;
> > +	}
> > +
> >  	/*
> >  	 * Try again to invalidate clean pages which might have been cached by
> >  	 * non-direct readahead, or faulted in by get_user_pages() if the source
> >  	 * of the write was an mmap'ed region of the file we're writing.  Either
> >  	 * one is a pretty crazy thing to do, so we don't support it 100%.  If
> >  	 * this invalidation fails, tough, the write still worked...
> > +	 *
> > +	 * And this page cache invalidation has to be after dio->end_io(), as
> > +	 * some filesystems convert unwritten extents to real allocations in
> > +	 * end_io() when necessary, otherwise a racing buffer read would cache
> > +	 * zeros from unwritten extents.
> >  	 */
> >  	if (ret > 0 && dio->op == REQ_OP_WRITE &&
> >  	    dio->inode->i_mapping->nrpages) {
> > @@ -274,14 +286,6 @@ static ssize_t dio_complete(struct dio *dio, ssize_t ret, bool is_async)
> >  		WARN_ON_ONCE(err);
> >  	}
> >  
> > -	if (dio->end_io) {
> > -
> > -		// XXX: ki_pos??
> > -		err = dio->end_io(dio->iocb, offset, ret, dio->private);
> > -		if (err)
> > -			ret = err;
> > -	}
> > -
> >  	if (!(dio->flags & DIO_SKIP_DIO_COUNT))
> >  		inode_dio_end(dio->inode);
> >  
> > diff --git a/fs/iomap.c b/fs/iomap.c
> > index be61cf742b5e..d4801f8dd4fd 100644
> > --- a/fs/iomap.c
> > +++ b/fs/iomap.c
> > @@ -714,23 +714,9 @@ static ssize_t iomap_dio_complete(struct iomap_dio *dio)
> >  {
> >  	struct kiocb *iocb = dio->iocb;
> >  	struct inode *inode = file_inode(iocb->ki_filp);
> > +	loff_t offset = iocb->ki_pos;
> >  	ssize_t ret;
> >  
> > -	/*
> > -	 * Try again to invalidate clean pages which might have been cached by
> > -	 * non-direct readahead, or faulted in by get_user_pages() if the source
> > -	 * of the write was an mmap'ed region of the file we're writing.  Either
> > -	 * one is a pretty crazy thing to do, so we don't support it 100%.  If
> > -	 * this invalidation fails, tough, the write still worked...
> > -	 */
> > -	if (!dio->error &&
> > -	    (dio->flags & IOMAP_DIO_WRITE) && inode->i_mapping->nrpages) {
> > -		ret = invalidate_inode_pages2_range(inode->i_mapping,
> > -				iocb->ki_pos >> PAGE_SHIFT,
> > -				(iocb->ki_pos + dio->size - 1) >> PAGE_SHIFT);
> > -		WARN_ON_ONCE(ret);
> > -	}
> > -
> >  	if (dio->end_io) {
> >  		ret = dio->end_io(iocb,
> >  				dio->error ? dio->error : dio->size,
> > @@ -742,12 +728,33 @@ static ssize_t iomap_dio_complete(struct iomap_dio *dio)
> >  	if (likely(!ret)) {
> >  		ret = dio->size;
> >  		/* check for short read */
> > -		if (iocb->ki_pos + ret > dio->i_size &&
> > +		if (offset + ret > dio->i_size &&
> >  		    !(dio->flags & IOMAP_DIO_WRITE))
> > -			ret = dio->i_size - iocb->ki_pos;
> > +			ret = dio->i_size - offset;
> >  		iocb->ki_pos += ret;
> >  	}
> >  
> > +	/*
> > +	 * Try again to invalidate clean pages which might have been cached by
> > +	 * non-direct readahead, or faulted in by get_user_pages() if the source
> > +	 * of the write was an mmap'ed region of the file we're writing.  Either
> > +	 * one is a pretty crazy thing to do, so we don't support it 100%.  If
> > +	 * this invalidation fails, tough, the write still worked...
> > +	 *
> > +	 * And this page cache invalidation has to be after dio->end_io(), as
> > +	 * some filesystems convert unwritten extents to real allocations in
> > +	 * end_io() when necessary, otherwise a racing buffer read would cache
> > +	 * zeros from unwritten extents.
> > +	 */
> > +	if (!dio->error &&
> > +	    (dio->flags & IOMAP_DIO_WRITE) && inode->i_mapping->nrpages) {
> > +		int err;
> > +		err = invalidate_inode_pages2_range(inode->i_mapping,
> > +				offset >> PAGE_SHIFT,
> > +				(offset + dio->size - 1) >> PAGE_SHIFT);
> > +		WARN_ON_ONCE(err);
> > +	}
> > +
> >  	inode_dio_end(file_inode(iocb->ki_filp));
> >  	kfree(dio);
> >  
> > -- 
> > 2.13.6
> > 

Re: [PATCH] fs: invalidate page cache after end_io() in dio completion

[Darrick J. Wong]

On Wed, Oct 04, 2017 at 12:02:01AM +0800, Eryu Guan wrote:
> Commit 332391a9935d ("fs: Fix page cache inconsistency when mixing
> buffered and AIO DIO") moved page cache invalidation from
> iomap_dio_rw() to iomap_dio_complete() for iomap based direct write
> path, but before the dio->end_io() call, and it re-introdued the bug
> fixed by commit c771c14baa33 ("iomap: invalidate page caches should
> be after iomap_dio_complete() in direct write").
> 
> I found this because fstests generic/418 started failing on XFS with
> v4.14-rc3 kernel, which is the regression test for this specific
> bug.
> 
> So similarly, fix it by moving dio->end_io() (which does the
> unwritten extent conversion) before page cache invalidation, to make
> sure next buffer read reads the final real allocations not unwritten
> extents. I also add some comments about why should end_io() go first
> in case we get it wrong again in the future.
> 
> Note that, there's no such problem in the non-iomap based direct
> write path, because we didn't remove the page cache invalidation
> after the ->direct_IO() in generic_file_direct_write() call, but I
> decided to fix dio_complete() too so we don't leave a landmine
> there, also be consistent with iomap_dio_complete().
> 
> Fixes: 332391a9935d ("fs: Fix page cache inconsistency when mixing buffered and AIO DIO")
> Signed-off-by: Eryu Guan <eguan@redhat.com>

Looks ok,
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>

I've picked this up for the xfs tree.

--D

> ---
>  fs/direct-io.c | 20 ++++++++++++--------
>  fs/iomap.c     | 41 ++++++++++++++++++++++++-----------------
>  2 files changed, 36 insertions(+), 25 deletions(-)
> 
> diff --git a/fs/direct-io.c b/fs/direct-io.c
> index 62cf812ed0e5..1dba6842c349 100644
> --- a/fs/direct-io.c
> +++ b/fs/direct-io.c
> @@ -259,12 +259,24 @@ static ssize_t dio_complete(struct dio *dio, ssize_t ret, bool is_async)
>  	if (ret == 0)
>  		ret = transferred;
>  
> +	if (dio->end_io) {
> +		// XXX: ki_pos??
> +		err = dio->end_io(dio->iocb, offset, ret, dio->private);
> +		if (err)
> +			ret = err;
> +	}
> +
>  	/*
>  	 * Try again to invalidate clean pages which might have been cached by
>  	 * non-direct readahead, or faulted in by get_user_pages() if the source
>  	 * of the write was an mmap'ed region of the file we're writing.  Either
>  	 * one is a pretty crazy thing to do, so we don't support it 100%.  If
>  	 * this invalidation fails, tough, the write still worked...
> +	 *
> +	 * And this page cache invalidation has to be after dio->end_io(), as
> +	 * some filesystems convert unwritten extents to real allocations in
> +	 * end_io() when necessary, otherwise a racing buffer read would cache
> +	 * zeros from unwritten extents.
>  	 */
>  	if (ret > 0 && dio->op == REQ_OP_WRITE &&
>  	    dio->inode->i_mapping->nrpages) {
> @@ -274,14 +286,6 @@ static ssize_t dio_complete(struct dio *dio, ssize_t ret, bool is_async)
>  		WARN_ON_ONCE(err);
>  	}
>  
> -	if (dio->end_io) {
> -
> -		// XXX: ki_pos??
> -		err = dio->end_io(dio->iocb, offset, ret, dio->private);
> -		if (err)
> -			ret = err;
> -	}
> -
>  	if (!(dio->flags & DIO_SKIP_DIO_COUNT))
>  		inode_dio_end(dio->inode);
>  
> diff --git a/fs/iomap.c b/fs/iomap.c
> index be61cf742b5e..d4801f8dd4fd 100644
> --- a/fs/iomap.c
> +++ b/fs/iomap.c
> @@ -714,23 +714,9 @@ static ssize_t iomap_dio_complete(struct iomap_dio *dio)
>  {
>  	struct kiocb *iocb = dio->iocb;
>  	struct inode *inode = file_inode(iocb->ki_filp);
> +	loff_t offset = iocb->ki_pos;
>  	ssize_t ret;
>  
> -	/*
> -	 * Try again to invalidate clean pages which might have been cached by
> -	 * non-direct readahead, or faulted in by get_user_pages() if the source
> -	 * of the write was an mmap'ed region of the file we're writing.  Either
> -	 * one is a pretty crazy thing to do, so we don't support it 100%.  If
> -	 * this invalidation fails, tough, the write still worked...
> -	 */
> -	if (!dio->error &&
> -	    (dio->flags & IOMAP_DIO_WRITE) && inode->i_mapping->nrpages) {
> -		ret = invalidate_inode_pages2_range(inode->i_mapping,
> -				iocb->ki_pos >> PAGE_SHIFT,
> -				(iocb->ki_pos + dio->size - 1) >> PAGE_SHIFT);
> -		WARN_ON_ONCE(ret);
> -	}
> -
>  	if (dio->end_io) {
>  		ret = dio->end_io(iocb,
>  				dio->error ? dio->error : dio->size,
> @@ -742,12 +728,33 @@ static ssize_t iomap_dio_complete(struct iomap_dio *dio)
>  	if (likely(!ret)) {
>  		ret = dio->size;
>  		/* check for short read */
> -		if (iocb->ki_pos + ret > dio->i_size &&
> +		if (offset + ret > dio->i_size &&
>  		    !(dio->flags & IOMAP_DIO_WRITE))
> -			ret = dio->i_size - iocb->ki_pos;
> +			ret = dio->i_size - offset;
>  		iocb->ki_pos += ret;
>  	}
>  
> +	/*
> +	 * Try again to invalidate clean pages which might have been cached by
> +	 * non-direct readahead, or faulted in by get_user_pages() if the source
> +	 * of the write was an mmap'ed region of the file we're writing.  Either
> +	 * one is a pretty crazy thing to do, so we don't support it 100%.  If
> +	 * this invalidation fails, tough, the write still worked...
> +	 *
> +	 * And this page cache invalidation has to be after dio->end_io(), as
> +	 * some filesystems convert unwritten extents to real allocations in
> +	 * end_io() when necessary, otherwise a racing buffer read would cache
> +	 * zeros from unwritten extents.
> +	 */
> +	if (!dio->error &&
> +	    (dio->flags & IOMAP_DIO_WRITE) && inode->i_mapping->nrpages) {
> +		int err;
> +		err = invalidate_inode_pages2_range(inode->i_mapping,
> +				offset >> PAGE_SHIFT,
> +				(offset + dio->size - 1) >> PAGE_SHIFT);
> +		WARN_ON_ONCE(err);
> +	}
> +
>  	inode_dio_end(file_inode(iocb->ki_filp));
>  	kfree(dio);
>  
> -- 
> 2.13.6
> 
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