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Date:   Mon, 16 Oct 2023 22:35:45 +0200
From:   Ahelenia =?utf-8?Q?Ziemia=C5=84ska?= 
        <nabijaczleweli@nabijaczleweli.xyz>
Cc:     Steven Rostedt <rostedt@goodmis.org>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org
Subject: [PATCH 04/11] tracing: tracing_buffers_splice_read: behave as-if
 non-blocking I/O
Message-ID: <1b84f2e4e5eaad501ff7b2bb03e2ad2f25ecdf14.1697486714.git.nabijaczleweli@nabijaczleweli.xyz>
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Otherwise we risk sleeping with the pipe locked for indeterminate
lengths of time.

Link: https://lore.kernel.org/linux-fsdevel/qk6hjuam54khlaikf2ssom6custxf5i=
s2ekkaequf4hvode3ls@zgf7j5j4ubvw/t/#u
Signed-off-by: Ahelenia Ziemia=C5=84ska <nabijaczleweli@nabijaczleweli.xyz>
---
 kernel/trace/trace.c | 32 ++++----------------------------
 1 file changed, 4 insertions(+), 28 deletions(-)

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;
=20
- again:
 	trace_access_lock(iter->cpu_file);
 	entries =3D ring_buffer_entries_cpu(iter->array_buffer->buffer, iter->cpu=
_file);
=20
@@ -8528,35 +8527,12 @@ tracing_buffers_splice_read(struct file *file, loff=
_t *ppos,
=20
 	/* did we read anything? */
 	if (!spd.nr_pages) {
-		long wait_index;
-
-		if (ret)
-			goto out;
-
-		ret =3D -EAGAIN;
-		if ((file->f_flags & O_NONBLOCK) || (flags & SPLICE_F_NONBLOCK))
-			goto out;
-
-		wait_index =3D READ_ONCE(iter->wait_index);
-
-		ret =3D 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 !=3D iter->wait_index)
-			goto out;
-
-		goto again;
+		if (!ret)
+			ret =3D -EAGAIN;
+	} else {
+		ret =3D splice_to_pipe(pipe, &spd);
 	}
=20
-	ret =3D splice_to_pipe(pipe, &spd);
-out:
 	splice_shrink_spd(&spd);
=20
 	return ret;
--=20
2.39.2

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