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@xxxxxxxxxxxxxxxxxx>
Reviewed-by: Amir Goldstein <amir73il@xxxxxxxxx>
Acked-by: Jan Kara <jack@xxxxxxx>
---
fs/splice.c | 31 ++++++++++++++-----------------
1 file changed, 14 insertions(+), 17 deletions(-)
diff --git a/fs/splice.c b/fs/splice.c
index 3e06611d19ae..6ae6da52eba9 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 +1180,11 @@ 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) {
+ } else if (opipe) {
if (off_out)
return -ESPIPE;
if (off_in) {
@@ -1209,18 +1200,24 @@ 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) {
+ /*
+ * Generate modify out before access in:
+ * do_splice_from() may've already sent modify out,
+ * and this ensures the events get merged.
+ */
+ fsnotify_modify(out);
+ fsnotify_access(in);
}
- return -EINVAL;
+ return ret;
}
static long __do_splice(struct file *in, loff_t __user *off_in,
--
2.39.2
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