This is a note to let you know that I've just added the patch titled
tracing: Use .flush() call to wake up readers
to the 6.6-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
tracing-use-.flush-call-to-wake-up-readers.patch
and it can be found in the queue-6.6 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From e5d7c1916562f0e856eb3d6f569629fcd535fed2 Mon Sep 17 00:00:00 2001
From: "Steven Rostedt (Google)" <rostedt@xxxxxxxxxxx>
Date: Fri, 8 Mar 2024 15:24:05 -0500
Subject: tracing: Use .flush() call to wake up readers
From: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
commit e5d7c1916562f0e856eb3d6f569629fcd535fed2 upstream.
The .release() function does not get called until all readers of a file
descriptor are finished.
If a thread is blocked on reading a file descriptor in ring_buffer_wait(),
and another thread closes the file descriptor, it will not wake up the
other thread as ring_buffer_wake_waiters() is called by .release(), and
that will not get called until the .read() is finished.
The issue originally showed up in trace-cmd, but the readers are actually
other processes with their own file descriptors. So calling close() would wake
up the other tasks because they are blocked on another descriptor then the
one that was closed(). But there's other wake ups that solve that issue.
When a thread is blocked on a read, it can still hang even when another
thread closed its descriptor.
This is what the .flush() callback is for. Have the .flush() wake up the
readers.
Link: https://lore.kernel.org/linux-trace-kernel/20240308202432.107909457@xxxxxxxxxxx
Cc: stable@xxxxxxxxxxxxxxx
Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
Cc: Mark Rutland <mark.rutland@xxxxxxx>
Cc: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: linke li <lilinke99@xxxxxx>
Cc: Rabin Vincent <rabin@xxxxxx>
Fixes: f3ddb74ad0790 ("tracing: Wake up ring buffer waiters on closing of the file")
Signed-off-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
kernel/trace/trace.c | 21 +++++++++++++++------
1 file changed, 15 insertions(+), 6 deletions(-)
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -8359,6 +8359,20 @@ tracing_buffers_read(struct file *filp,
return size;
}
+static int tracing_buffers_flush(struct file *file, fl_owner_t id)
+{
+ struct ftrace_buffer_info *info = file->private_data;
+ struct trace_iterator *iter = &info->iter;
+
+ iter->wait_index++;
+ /* Make sure the waiters see the new wait_index */
+ smp_wmb();
+
+ ring_buffer_wake_waiters(iter->array_buffer->buffer, iter->cpu_file);
+
+ return 0;
+}
+
static int tracing_buffers_release(struct inode *inode, struct file *file)
{
struct ftrace_buffer_info *info = file->private_data;
@@ -8370,12 +8384,6 @@ static int tracing_buffers_release(struc
__trace_array_put(iter->tr);
- iter->wait_index++;
- /* Make sure the waiters see the new wait_index */
- smp_wmb();
-
- ring_buffer_wake_waiters(iter->array_buffer->buffer, iter->cpu_file);
-
if (info->spare)
ring_buffer_free_read_page(iter->array_buffer->buffer,
info->spare_cpu, info->spare);
@@ -8589,6 +8597,7 @@ static const struct file_operations trac
.read = tracing_buffers_read,
.poll = tracing_buffers_poll,
.release = tracing_buffers_release,
+ .flush = tracing_buffers_flush,
.splice_read = tracing_buffers_splice_read,
.unlocked_ioctl = tracing_buffers_ioctl,
.llseek = no_llseek,
Patches currently in stable-queue which might be from rostedt@xxxxxxxxxxx are
queue-6.6/ring-buffer-fix-resetting-of-shortest_full.patch
queue-6.6/ring-buffer-use-wait_event_interruptible-in-ring_buf.patch
queue-6.6/drm-i915-add-missing-to-__assign_str-macros-in-trace.patch
queue-6.6/cxl-trace-properly-initialize-cxl_poison-region-name.patch
queue-6.6/ring-buffer-fix-full_waiters_pending-in-poll.patch
queue-6.6/net-hns3-tracing-fix-hclgevf-trace-event-strings.patch
queue-6.6/ring-buffer-do-not-set-shortest_full-when-full-targe.patch
queue-6.6/nfsd-fix-nfsd_clid_class-use-of-__string_len-macro.patch
queue-6.6/ring-buffer-fix-waking-up-ring-buffer-readers.patch
queue-6.6/tracing-use-.flush-call-to-wake-up-readers.patch
