Patch "tracing: Allocate the snapshot buffer before enabling probe" has been added to the 4.4-stable tree

Patch "tracing: Allocate the snapshot buffer before enabling probe" has been added to the 4.4-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

    tracing: Allocate the snapshot buffer before enabling probe

to the 4.4-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-allocate-the-snapshot-buffer-before-enabling-probe.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From df62db5be2e5f070ecd1a5ece5945b590ee112e0 Mon Sep 17 00:00:00 2001
From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>
Date: Wed, 19 Apr 2017 12:07:08 -0400
Subject: tracing: Allocate the snapshot buffer before enabling probe

From: Steven Rostedt (VMware) <rostedt@goodmis.org>

commit df62db5be2e5f070ecd1a5ece5945b590ee112e0 upstream.

Currently the snapshot trigger enables the probe and then allocates the
snapshot. If the probe triggers before the allocation, it could cause the
snapshot to fail and turn tracing off. It's best to allocate the snapshot
buffer first, and then enable the trigger. If something goes wrong in the
enabling of the trigger, the snapshot buffer is still allocated, but it can
also be freed by the user by writting zero into the snapshot buffer file.

Also add a check of the return status of alloc_snapshot().

Fixes: 77fd5c15e3 ("tracing: Add snapshot trigger to function probes")
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 kernel/trace/trace.c |    8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -6060,11 +6060,13 @@ ftrace_trace_snapshot_callback(struct ft
 		return ret;
 
  out_reg:
-	ret = register_ftrace_function_probe(glob, ops, count);
+	ret = alloc_snapshot(&global_trace);
+	if (ret < 0)
+		goto out;
 
-	if (ret >= 0)
-		alloc_snapshot(&global_trace);
+	ret = register_ftrace_function_probe(glob, ops, count);
 
+ out:
 	return ret < 0 ? ret : 0;
 }
 


Patches currently in stable-queue which might be from rostedt@goodmis.org are

queue-4.4/tracing-allocate-the-snapshot-buffer-before-enabling-probe.patch
queue-4.4/ring-buffer-have-ring_buffer_iter_empty-return-true-when-empty.patch