[v2] splice: only read in as much information as there is pipe buffer space
diff mbox series

Message ID 20190830210603.GB5340@magnolia
State New
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Series
  • [v2] splice: only read in as much information as there is pipe buffer space
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Commit Message

Darrick J. Wong Aug. 30, 2019, 9:06 p.m. UTC
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>
---
v2: tidy up the other call site per Andreas' request
---
 fs/splice.c |   17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

Comments

Darrick J. Wong Sept. 5, 2019, 3:42 a.m. UTC | #1
On Fri, Aug 30, 2019 at 02:06:03PM -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>
> ---
> v2: tidy up the other call site per Andreas' request

Ping?  Anyone want to add a RVB to this?

--D

> ---
>  fs/splice.c |   17 ++++++++++++++---
>  1 file changed, 14 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/splice.c b/fs/splice.c
> index 98412721f056..2ddbace9129f 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) {
> +		unsigned int 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, (size_t)pipe_pages << PAGE_SHIFT);
>  		ret = do_splice_to(in, &pos, pipe, read_len, flags);
>  		if (unlikely(ret <= 0))
>  			goto out_release;
> @@ -1101,6 +1102,7 @@ static long do_splice(struct file *in, loff_t __user *off_in,
>  	struct pipe_inode_info *ipipe;
>  	struct pipe_inode_info *opipe;
>  	loff_t offset;
> +	unsigned int pipe_pages;
>  	long ret;
>  
>  	ipipe = get_pipe_info(in);
> @@ -1123,6 +1125,10 @@ static long do_splice(struct file *in, loff_t __user *off_in,
>  		if ((in->f_flags | out->f_flags) & O_NONBLOCK)
>  			flags |= SPLICE_F_NONBLOCK;
>  
> +		/* Don't try to read more the pipe has space for. */
> +		pipe_pages = opipe->buffers - opipe->nrbufs;
> +		len = min(len, (size_t)pipe_pages << PAGE_SHIFT);
> +
>  		return splice_pipe_to_pipe(ipipe, opipe, len, flags);
>  	}
>  
> @@ -1180,8 +1186,13 @@ 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) {
> +			/* Don't try to read more the pipe has space for. */
> +			pipe_pages = opipe->buffers - opipe->nrbufs;
> +			len = min(len, (size_t)pipe_pages << PAGE_SHIFT);
> +
>  			ret = do_splice_to(in, &offset, opipe, len, flags);
> +		}
>  		pipe_unlock(opipe);
>  		if (ret > 0)
>  			wakeup_pipe_readers(opipe);
Andreas Grünbacher Sept. 17, 2019, 1:17 p.m. UTC | #2
Am Do., 5. Sept. 2019 um 05:42 Uhr schrieb Darrick J. Wong
<darrick.wong@oracle.com>:
> On Fri, Aug 30, 2019 at 02:06:03PM -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>
> > ---
> > v2: tidy up the other call site per Andreas' request
>
> Ping?  Anyone want to add a RVB to this?

You can add the following:

Reviewed-by: Andreas Grünbacher <agruenba@redhat.com>
Tested-by: Andreas Grünbacher <agruenba@redhat.com>

And could you please update the email address in the reported-by tag as well?

Is this going to go in via the xfs tree?

Thanks,
Andreas
Darrick J. Wong Sept. 17, 2019, 4:46 p.m. UTC | #3
On Tue, Sep 17, 2019 at 03:17:22PM +0200, Andreas Grünbacher wrote:
> Am Do., 5. Sept. 2019 um 05:42 Uhr schrieb Darrick J. Wong
> <darrick.wong@oracle.com>:
> > On Fri, Aug 30, 2019 at 02:06:03PM -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>
> > > ---
> > > v2: tidy up the other call site per Andreas' request
> >
> > Ping?  Anyone want to add a RVB to this?
> 
> You can add the following:
> 
> Reviewed-by: Andreas Grünbacher <agruenba@redhat.com>
> Tested-by: Andreas Grünbacher <agruenba@redhat.com>
> 
> And could you please update the email address in the reported-by tag as well?

Done.

> Is this going to go in via the xfs tree?

I'll let it soak in -next for a few days and send a single-patch pull
request for it.

(I'm sending out pull requests today for the things that have been
ready to go for the last couple of weeks.)

--D

> Thanks,
> Andreas
Andreas Grünbacher Sept. 17, 2019, 5 p.m. UTC | #4
Am Di., 17. Sept. 2019 um 18:46 Uhr schrieb Darrick J. Wong
<darrick.wong@oracle.com>:
> > Is this going to go in via the xfs tree?
>
> I'll let it soak in -next for a few days and send a single-patch pull
> request for it.
>
> (I'm sending out pull requests today for the things that have been
> ready to go for the last couple of weeks.)

Okay, works for me.

Thanks,
Andreas
Darrick J. Wong Sept. 19, 2019, 10:39 p.m. UTC | #5
On Tue, Sep 17, 2019 at 07:00:15PM +0200, Andreas Grünbacher wrote:
> Am Di., 17. Sept. 2019 um 18:46 Uhr schrieb Darrick J. Wong
> <darrick.wong@oracle.com>:
> > > Is this going to go in via the xfs tree?
> >
> > I'll let it soak in -next for a few days and send a single-patch pull
> > request for it.
> >
> > (I'm sending out pull requests today for the things that have been
> > ready to go for the last couple of weeks.)
> 
> Okay, works for me.

Heh, syzbot found a bug[1] in this patch, so I'm withdrawing it for now.

--D

[1] https://lore.kernel.org/linux-fsdevel/20190919211013.GN5340@magnolia/T/

> Thanks,
> Andreas

Patch
diff mbox series

diff --git a/fs/splice.c b/fs/splice.c
index 98412721f056..2ddbace9129f 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) {
+		unsigned int 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, (size_t)pipe_pages << PAGE_SHIFT);
 		ret = do_splice_to(in, &pos, pipe, read_len, flags);
 		if (unlikely(ret <= 0))
 			goto out_release;
@@ -1101,6 +1102,7 @@  static long do_splice(struct file *in, loff_t __user *off_in,
 	struct pipe_inode_info *ipipe;
 	struct pipe_inode_info *opipe;
 	loff_t offset;
+	unsigned int pipe_pages;
 	long ret;
 
 	ipipe = get_pipe_info(in);
@@ -1123,6 +1125,10 @@  static long do_splice(struct file *in, loff_t __user *off_in,
 		if ((in->f_flags | out->f_flags) & O_NONBLOCK)
 			flags |= SPLICE_F_NONBLOCK;
 
+		/* Don't try to read more the pipe has space for. */
+		pipe_pages = opipe->buffers - opipe->nrbufs;
+		len = min(len, (size_t)pipe_pages << PAGE_SHIFT);
+
 		return splice_pipe_to_pipe(ipipe, opipe, len, flags);
 	}
 
@@ -1180,8 +1186,13 @@  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) {
+			/* Don't try to read more the pipe has space for. */
+			pipe_pages = opipe->buffers - opipe->nrbufs;
+			len = min(len, (size_t)pipe_pages << PAGE_SHIFT);
+
 			ret = do_splice_to(in, &offset, opipe, len, flags);
+		}
 		pipe_unlock(opipe);
 		if (ret > 0)
 			wakeup_pipe_readers(opipe);