[PATCH v4] splice: only read in as much information as there is pipe buffer space

[PATCH v4] splice: only read in as much information as there is pipe buffer space

[Darrick J. Wong]

From: Darrick J. Wong <darrick.wong@oracle.com>

Andreas Grünbacher reports that on the two filesystems that support
iomap directio, it's possible for splice() to return -EAGAIN (instead of
a short splice) if the pipe being written to has less space available in
its pipe buffers than the length supplied by the calling process.

Months ago we fixed splice_direct_to_actor to clamp the length of the
read request to the size of the splice pipe.  Do the same to do_splice.

Fixes: 17614445576b6 ("splice: don't read more than available pipe space")
Reported-by: Andreas Grünbacher <andreas.gruenbacher@gmail.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
---
v4: use size_t for pipe_pages
---
 fs/splice.c |   14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/fs/splice.c b/fs/splice.c
index 98412721f056..9b9b22d2215a 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -945,12 +945,13 @@ ssize_t splice_direct_to_actor(struct file *in, struct splice_desc *sd,
 	WARN_ON_ONCE(pipe->nrbufs != 0);
 
 	while (len) {
+		size_t pipe_pages;
 		size_t read_len;
 		loff_t pos = sd->pos, prev_pos = pos;
 
 		/* Don't try to read more the pipe has space for. */
-		read_len = min_t(size_t, len,
-				 (pipe->buffers - pipe->nrbufs) << PAGE_SHIFT);
+		pipe_pages = pipe->buffers - pipe->nrbufs;
+		read_len = min(len, pipe_pages << PAGE_SHIFT);
 		ret = do_splice_to(in, &pos, pipe, read_len, flags);
 		if (unlikely(ret <= 0))
 			goto out_release;
@@ -1180,8 +1181,15 @@ static long do_splice(struct file *in, loff_t __user *off_in,
 
 		pipe_lock(opipe);
 		ret = wait_for_space(opipe, flags);
-		if (!ret)
+		if (!ret) {
+			size_t pipe_pages;
+
+			/* Don't try to read more the pipe has space for. */
+			pipe_pages = opipe->buffers - opipe->nrbufs;
+			len = min(len, pipe_pages << PAGE_SHIFT);
+
 			ret = do_splice_to(in, &offset, opipe, len, flags);
+		}
 		pipe_unlock(opipe);
 		if (ret > 0)
 			wakeup_pipe_readers(opipe);

Re: [PATCH v4] splice: only read in as much information as there is pipe buffer space

[Darrick J. Wong]

Ping?  Can /someone/ please review this?

--D

On Sat, Oct 19, 2019 at 09:11:38AM -0700, Darrick J. Wong wrote:
> From: Darrick J. Wong <darrick.wong@oracle.com>
> 
> Andreas Grünbacher reports that on the two filesystems that support
> iomap directio, it's possible for splice() to return -EAGAIN (instead of
> a short splice) if the pipe being written to has less space available in
> its pipe buffers than the length supplied by the calling process.
> 
> Months ago we fixed splice_direct_to_actor to clamp the length of the
> read request to the size of the splice pipe.  Do the same to do_splice.
> 
> Fixes: 17614445576b6 ("splice: don't read more than available pipe space")
> Reported-by: Andreas Grünbacher <andreas.gruenbacher@gmail.com>
> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> ---
> v4: use size_t for pipe_pages
> ---
>  fs/splice.c |   14 +++++++++++---
>  1 file changed, 11 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/splice.c b/fs/splice.c
> index 98412721f056..9b9b22d2215a 100644
> --- a/fs/splice.c
> +++ b/fs/splice.c
> @@ -945,12 +945,13 @@ ssize_t splice_direct_to_actor(struct file *in, struct splice_desc *sd,
>  	WARN_ON_ONCE(pipe->nrbufs != 0);
>  
>  	while (len) {
> +		size_t pipe_pages;
>  		size_t read_len;
>  		loff_t pos = sd->pos, prev_pos = pos;
>  
>  		/* Don't try to read more the pipe has space for. */
> -		read_len = min_t(size_t, len,
> -				 (pipe->buffers - pipe->nrbufs) << PAGE_SHIFT);
> +		pipe_pages = pipe->buffers - pipe->nrbufs;
> +		read_len = min(len, pipe_pages << PAGE_SHIFT);
>  		ret = do_splice_to(in, &pos, pipe, read_len, flags);
>  		if (unlikely(ret <= 0))
>  			goto out_release;
> @@ -1180,8 +1181,15 @@ static long do_splice(struct file *in, loff_t __user *off_in,
>  
>  		pipe_lock(opipe);
>  		ret = wait_for_space(opipe, flags);
> -		if (!ret)
> +		if (!ret) {
> +			size_t pipe_pages;
> +
> +			/* Don't try to read more the pipe has space for. */
> +			pipe_pages = opipe->buffers - opipe->nrbufs;
> +			len = min(len, pipe_pages << PAGE_SHIFT);
> +
>  			ret = do_splice_to(in, &offset, opipe, len, flags);
> +		}
>  		pipe_unlock(opipe);
>  		if (ret > 0)
>  			wakeup_pipe_readers(opipe);

Re: [PATCH v4] splice: only read in as much information as there is pipe buffer space

[Andreas Gruenbacher]

On Sat, Oct 19, 2019 at 6:14 PM Darrick J. Wong <darrick.wong@oracle.com> wrote:
> From: Darrick J. Wong <darrick.wong@oracle.com>
>
> Andreas Grünbacher reports that on the two filesystems that support
> iomap directio, it's possible for splice() to return -EAGAIN (instead of
> a short splice) if the pipe being written to has less space available in
> its pipe buffers than the length supplied by the calling process.
>
> Months ago we fixed splice_direct_to_actor to clamp the length of the
> read request to the size of the splice pipe.  Do the same to do_splice.
>
> Fixes: 17614445576b6 ("splice: don't read more than available pipe space")
> Reported-by: Andreas Grünbacher <andreas.gruenbacher@gmail.com>

Reviewed-by: Andreas Grünbacher <andreas.gruenbacher@gmail.com>

> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> ---
> v4: use size_t for pipe_pages
> ---
>  fs/splice.c |   14 +++++++++++---
>  1 file changed, 11 insertions(+), 3 deletions(-)
>
> diff --git a/fs/splice.c b/fs/splice.c
> index 98412721f056..9b9b22d2215a 100644
> --- a/fs/splice.c
> +++ b/fs/splice.c
> @@ -945,12 +945,13 @@ ssize_t splice_direct_to_actor(struct file *in, struct splice_desc *sd,
>         WARN_ON_ONCE(pipe->nrbufs != 0);
>
>         while (len) {
> +               size_t pipe_pages;
>                 size_t read_len;
>                 loff_t pos = sd->pos, prev_pos = pos;
>
>                 /* Don't try to read more the pipe has space for. */
> -               read_len = min_t(size_t, len,
> -                                (pipe->buffers - pipe->nrbufs) << PAGE_SHIFT);
> +               pipe_pages = pipe->buffers - pipe->nrbufs;
> +               read_len = min(len, pipe_pages << PAGE_SHIFT);
>                 ret = do_splice_to(in, &pos, pipe, read_len, flags);
>                 if (unlikely(ret <= 0))
>                         goto out_release;
> @@ -1180,8 +1181,15 @@ static long do_splice(struct file *in, loff_t __user *off_in,
>
>                 pipe_lock(opipe);
>                 ret = wait_for_space(opipe, flags);
> -               if (!ret)
> +               if (!ret) {
> +                       size_t pipe_pages;
> +
> +                       /* Don't try to read more the pipe has space for. */
> +                       pipe_pages = opipe->buffers - opipe->nrbufs;
> +                       len = min(len, pipe_pages << PAGE_SHIFT);
> +
>                         ret = do_splice_to(in, &offset, opipe, len, flags);
> +               }
>                 pipe_unlock(opipe);
>                 if (ret > 0)
>                         wakeup_pipe_readers(opipe);

Re: [PATCH v4] splice: only read in as much information as there is pipe buffer space

[Darrick J. Wong]

On Thu, Nov 21, 2019 at 06:57:55PM +0100, Andreas Gruenbacher wrote:
> On Sat, Oct 19, 2019 at 6:14 PM Darrick J. Wong <darrick.wong@oracle.com> wrote:
> > From: Darrick J. Wong <darrick.wong@oracle.com>
> >
> > Andreas Grünbacher reports that on the two filesystems that support
> > iomap directio, it's possible for splice() to return -EAGAIN (instead of
> > a short splice) if the pipe being written to has less space available in
> > its pipe buffers than the length supplied by the calling process.
> >
> > Months ago we fixed splice_direct_to_actor to clamp the length of the
> > read request to the size of the splice pipe.  Do the same to do_splice.
> >
> > Fixes: 17614445576b6 ("splice: don't read more than available pipe space")
> > Reported-by: Andreas Grünbacher <andreas.gruenbacher@gmail.com>
> 
> Reviewed-by: Andreas Grünbacher <andreas.gruenbacher@gmail.com>

Cool, thanks.  I'll try to push this to Linus next week.

--D

> > Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> > ---
> > v4: use size_t for pipe_pages
> > ---
> >  fs/splice.c |   14 +++++++++++---
> >  1 file changed, 11 insertions(+), 3 deletions(-)
> >
> > diff --git a/fs/splice.c b/fs/splice.c
> > index 98412721f056..9b9b22d2215a 100644
> > --- a/fs/splice.c
> > +++ b/fs/splice.c
> > @@ -945,12 +945,13 @@ ssize_t splice_direct_to_actor(struct file *in, struct splice_desc *sd,
> >         WARN_ON_ONCE(pipe->nrbufs != 0);
> >
> >         while (len) {
> > +               size_t pipe_pages;
> >                 size_t read_len;
> >                 loff_t pos = sd->pos, prev_pos = pos;
> >
> >                 /* Don't try to read more the pipe has space for. */
> > -               read_len = min_t(size_t, len,
> > -                                (pipe->buffers - pipe->nrbufs) << PAGE_SHIFT);
> > +               pipe_pages = pipe->buffers - pipe->nrbufs;
> > +               read_len = min(len, pipe_pages << PAGE_SHIFT);
> >                 ret = do_splice_to(in, &pos, pipe, read_len, flags);
> >                 if (unlikely(ret <= 0))
> >                         goto out_release;
> > @@ -1180,8 +1181,15 @@ static long do_splice(struct file *in, loff_t __user *off_in,
> >
> >                 pipe_lock(opipe);
> >                 ret = wait_for_space(opipe, flags);
> > -               if (!ret)
> > +               if (!ret) {
> > +                       size_t pipe_pages;
> > +
> > +                       /* Don't try to read more the pipe has space for. */
> > +                       pipe_pages = opipe->buffers - opipe->nrbufs;
> > +                       len = min(len, pipe_pages << PAGE_SHIFT);
> > +
> >                         ret = do_splice_to(in, &offset, opipe, len, flags);
> > +               }
> >                 pipe_unlock(opipe);
> >                 if (ret > 0)
> >                         wakeup_pipe_readers(opipe);
> 

Re: [PATCH v4] splice: only read in as much information as there is pipe buffer space

[Andreas Grünbacher]

Am Fr., 22. Nov. 2019 um 02:24 Uhr schrieb Darrick J. Wong
<darrick.wong@oracle.com>:
> On Thu, Nov 21, 2019 at 06:57:55PM +0100, Andreas Gruenbacher wrote:
> > On Sat, Oct 19, 2019 at 6:14 PM Darrick J. Wong <darrick.wong@oracle.com> wrote:
> > > From: Darrick J. Wong <darrick.wong@oracle.com>
> > >
> > > Andreas Grünbacher reports that on the two filesystems that support
> > > iomap directio, it's possible for splice() to return -EAGAIN (instead of
> > > a short splice) if the pipe being written to has less space available in
> > > its pipe buffers than the length supplied by the calling process.
> > >
> > > Months ago we fixed splice_direct_to_actor to clamp the length of the
> > > read request to the size of the splice pipe.  Do the same to do_splice.
> > >
> > > Fixes: 17614445576b6 ("splice: don't read more than available pipe space")
> > > Reported-by: Andreas Grünbacher <andreas.gruenbacher@gmail.com>
> >
> > Reviewed-by: Andreas Grünbacher <andreas.gruenbacher@gmail.com>
>
> Cool, thanks.  I'll try to push this to Linus next week.

That would be great, thanks.

Andreas