diff mbox series

[v3,1/3] splice: always fsnotify_access(in), fsnotify_modify(out) on success

Message ID 8827a512f0974b9f261887d344c3b1ffde7b21e5.1687884031.git.nabijaczleweli@nabijaczleweli.xyz
State New
Headers
Series [v3,1/3] splice: always fsnotify_access(in), fsnotify_modify(out) on success |

Commit Message

Ahelenia Ziemiańska June 27, 2023, 4:55 p.m. UTC 
  The current behaviour caused an asymmetry where some write APIs
(write, sendfile) would notify the written-to/read-from objects,
but splice wouldn't.

This affected userspace which uses inotify, most notably coreutils
tail -f, to monitor pipes.
If the pipe buffer had been filled by a splice-family function:
  * tail wouldn't know and thus wouldn't service the pipe, and
  * all writes to the pipe would block because it's full,
thus service was denied.
(For the particular case of tail -f this could be worked around
 with ---disable-inotify.)

Fixes: 983652c69199 ("splice: report related fsnotify events")
Link: https://lore.kernel.org/linux-fsdevel/jbyihkyk5dtaohdwjyivambb2gffyjs3dodpofafnkkunxq7bu@jngkdxx65pux/t/#u
Link: https://bugs.debian.org/1039488
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
---
 fs/splice.c | 31 ++++++++++++++-----------------
 1 file changed, 14 insertions(+), 17 deletions(-)

Comments

Amir Goldstein June 27, 2023, 6:10 p.m. UTC | #1 
On Tue, Jun 27, 2023 at 7:55 PM Ahelenia Ziemiańska
<nabijaczleweli@nabijaczleweli.xyz> wrote:
>
> The current behaviour caused an asymmetry where some write APIs
> (write, sendfile) would notify the written-to/read-from objects,
> but splice wouldn't.
>
> This affected userspace which uses inotify, most notably coreutils
> tail -f, to monitor pipes.
> If the pipe buffer had been filled by a splice-family function:
>   * tail wouldn't know and thus wouldn't service the pipe, and
>   * all writes to the pipe would block because it's full,
> thus service was denied.
> (For the particular case of tail -f this could be worked around
>  with ---disable-inotify.)
>
> Fixes: 983652c69199 ("splice: report related fsnotify events")
> Link: https://lore.kernel.org/linux-fsdevel/jbyihkyk5dtaohdwjyivambb2gffyjs3dodpofafnkkunxq7bu@jngkdxx65pux/t/#u
> Link: https://bugs.debian.org/1039488
> Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
> Reviewed-by: Amir Goldstein <amir73il@gmail.com>
> ---
>  fs/splice.c | 31 ++++++++++++++-----------------
>  1 file changed, 14 insertions(+), 17 deletions(-)
>
> diff --git a/fs/splice.c b/fs/splice.c
> index 3e06611d19ae..e16f4f032d2f 100644
> --- a/fs/splice.c
> +++ b/fs/splice.c
> @@ -1154,10 +1154,8 @@ long do_splice(struct file *in, loff_t *off_in, struct file *out,
>                 if ((in->f_flags | out->f_flags) & O_NONBLOCK)
>                         flags |= SPLICE_F_NONBLOCK;
>
> -               return splice_pipe_to_pipe(ipipe, opipe, len, flags);
> -       }
> -
> -       if (ipipe) {
> +               ret = splice_pipe_to_pipe(ipipe, opipe, len, flags);
> +       } else if (ipipe) {
>                 if (off_in)
>                         return -ESPIPE;
>                 if (off_out) {
> @@ -1182,18 +1180,15 @@ long do_splice(struct file *in, loff_t *off_in, struct file *out,
>                 ret = do_splice_from(ipipe, out, &offset, len, flags);
>                 file_end_write(out);
>
> -               if (ret > 0)
> -                       fsnotify_modify(out);
> -
>                 if (!off_out)
>                         out->f_pos = offset;
>                 else
>                         *off_out = offset;
>
> -               return ret;
> -       }
> -
> -       if (opipe) {
> +               // splice_write-> already marked out
> +               // as modified via vfs_iter_write()
> +               goto noaccessout;
> +       } else if (opipe) {
>                 if (off_out)
>                         return -ESPIPE;
>                 if (off_in) {
> @@ -1209,18 +1204,20 @@ long do_splice(struct file *in, loff_t *off_in, struct file *out,
>
>                 ret = splice_file_to_pipe(in, opipe, &offset, len, flags);
>
> -               if (ret > 0)
> -                       fsnotify_access(in);
> -
>                 if (!off_in)
>                         in->f_pos = offset;
>                 else
>                         *off_in = offset;
> +       } else
> +               return -EINVAL;
>
> -               return ret;
> -       }
> +       if (ret > 0)
> +               fsnotify_modify(out);
> +noaccessout:
> +       if (ret > 0)
> +               fsnotify_access(in);
>

As I wrote, I don't like this special case.
I prefer that we generate double IN_MODIFY than
having to maintain unreadable code.

Let's see what Jan has to say about this.

Thanks,
Amir.
Ahelenia Ziemiańska June 27, 2023, 8:13 p.m. UTC | #2 
On Tue, Jun 27, 2023 at 09:10:09PM +0300, Amir Goldstein wrote:
> On Tue, Jun 27, 2023 at 7:55 PM Ahelenia Ziemiańska
> <nabijaczleweli@nabijaczleweli.xyz> wrote:
> > @@ -1209,18 +1204,20 @@ long do_splice(struct file *in, loff_t *off_in, struct file *out,
> >
> >                 ret = splice_file_to_pipe(in, opipe, &offset, len, flags);
> >
> > -               if (ret > 0)
> > -                       fsnotify_access(in);
> > -
> >                 if (!off_in)
> >                         in->f_pos = offset;
> >                 else
> >                         *off_in = offset;
> > +       } else
> > +               return -EINVAL;
> >
> > -               return ret;
> > -       }
> > +       if (ret > 0)
> > +               fsnotify_modify(out);
> > +noaccessout:
> > +       if (ret > 0)
> > +               fsnotify_access(in);
> >
> As I wrote, I don't like this special case.
> I prefer that we generate double IN_MODIFY than
> having to maintain unreadable code.
> 
> Let's see what Jan has to say about this.
Yes, in principle I definitely agree, but I don't know what the official
policy is on (effectively-)spurious/duplicate events; neither the kernel
documentation nor the manual speak to the reliability of the signal,
so I defaulted to the variant I thought to be correcter, if filthy.
diff mbox series

Patch

diff --git a/fs/splice.c b/fs/splice.c
index 3e06611d19ae..e16f4f032d2f 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -1154,10 +1154,8 @@  long do_splice(struct file *in, loff_t *off_in, struct file *out,
 		if ((in->f_flags | out->f_flags) & O_NONBLOCK)
 			flags |= SPLICE_F_NONBLOCK;
 
-		return splice_pipe_to_pipe(ipipe, opipe, len, flags);
-	}
-
-	if (ipipe) {
+		ret = splice_pipe_to_pipe(ipipe, opipe, len, flags);
+	} else if (ipipe) {
 		if (off_in)
 			return -ESPIPE;
 		if (off_out) {
@@ -1182,18 +1180,15 @@  long do_splice(struct file *in, loff_t *off_in, struct file *out,
 		ret = do_splice_from(ipipe, out, &offset, len, flags);
 		file_end_write(out);
 
-		if (ret > 0)
-			fsnotify_modify(out);
-
 		if (!off_out)
 			out->f_pos = offset;
 		else
 			*off_out = offset;
 
-		return ret;
-	}
-
-	if (opipe) {
+		// splice_write-> already marked out
+		// as modified via vfs_iter_write()
+		goto noaccessout;
+	} else if (opipe) {
 		if (off_out)
 			return -ESPIPE;
 		if (off_in) {
@@ -1209,18 +1204,20 @@  long do_splice(struct file *in, loff_t *off_in, struct file *out,
 
 		ret = splice_file_to_pipe(in, opipe, &offset, len, flags);
 
-		if (ret > 0)
-			fsnotify_access(in);
-
 		if (!off_in)
 			in->f_pos = offset;
 		else
 			*off_in = offset;
+	} else
+		return -EINVAL;
 
-		return ret;
-	}
+	if (ret > 0)
+		fsnotify_modify(out);
+noaccessout:
+	if (ret > 0)
+		fsnotify_access(in);
 
-	return -EINVAL;
+	return ret;
 }
 
 static long __do_splice(struct file *in, loff_t __user *off_in,