[RERESEND,04/11] tracing: tracing_buffers_splice_read: behave as-if non-blocking I/O

Commit Message

Ahelenia Ziemiańska Dec. 14, 2023, 6:45 p.m. UTC

Otherwise we risk sleeping with the pipe locked for indeterminate
lengths of time.

Link: https://lore.kernel.org/linux-fsdevel/qk6hjuam54khlaikf2ssom6custxf5is2ekkaequf4hvode3ls@zgf7j5j4ubvw/t/#u
Signed-off-by: Ahelenia Ziemiańska <[e-mail]>
---
 kernel/trace/trace.c | 32 ++++----------------------------
 1 file changed, 4 insertions(+), 28 deletions(-)

Comments

Steven Rostedt Dec. 20, 2023, 4:41 p.m. UTC | #1

On Thu, 14 Dec 2023 19:45:02 +0100
Ahelenia Ziemiańska <[e-mail]> wrote:

> Otherwise we risk sleeping with the pipe locked for indeterminate
> lengths of time.

This change log is really lacking.

Why is this an issue?

 
> Link: https://lore.kernel.org/linux-fsdevel/qk6hjuam54khlaikf2ssom6custxf5is2ekkaequf4hvode3ls@zgf7j5j4ubvw/t/#u

The change log should not rely on any external links. Those are for
reference only. At a bare minimum, the change log should have a tl;dr;
summary of the issue. The change log itself should have enough information
to understand why this change is happening without the need to look at any
links.

-- Steve

Patch

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index abaaf516fcae..9be7a4c0a3ca 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -8477,7 +8477,6 @@  tracing_buffers_splice_read(struct file *file, loff_t *ppos,
 	if (splice_grow_spd(pipe, &spd))
 		return -ENOMEM;
 
- again:
 	trace_access_lock(iter->cpu_file);
 	entries = ring_buffer_entries_cpu(iter->array_buffer->buffer, iter->cpu_file);
 
@@ -8528,35 +8527,12 @@  tracing_buffers_splice_read(struct file *file, loff_t *ppos,
 
 	/* did we read anything? */
 	if (!spd.nr_pages) {
-		long wait_index;
-
-		if (ret)
-			goto out;
-
-		ret = -EAGAIN;
-		if ((file->f_flags & O_NONBLOCK) || (flags & SPLICE_F_NONBLOCK))
-			goto out;
-
-		wait_index = READ_ONCE(iter->wait_index);
-
-		ret = wait_on_pipe(iter, iter->tr->buffer_percent);
-		if (ret)
-			goto out;
-
-		/* No need to wait after waking up when tracing is off */
-		if (!tracer_tracing_is_on(iter->tr))
-			goto out;
-
-		/* Make sure we see the new wait_index */
-		smp_rmb();
-		if (wait_index != iter->wait_index)
-			goto out;
-
-		goto again;
+		if (!ret)
+			ret = -EAGAIN;
+	} else {
+		ret = splice_to_pipe(pipe, &spd);
 	}
 
-	ret = splice_to_pipe(pipe, &spd);
-out:
 	splice_shrink_spd(&spd);
 
 	return ret;