[for-linus][PATCH 0/2] ftrace: Fixes for v6.13

[for-linus][PATCH 0/2] ftrace: Fixes for v6.13

[Steven Rostedt]

Fixes for ftrace in v6.13:

- Add needed READ_ONCE() around access to the fgraph array element

  The updates to the fgraph array can happen when callbacks are registered
  and unregistered. The __ftrace_return_to_handler() can handle reading
  either the old value or the new value. But once it reads that value
  it must stay consistent otherwise the check that looks to see if the
  value is a stub may show false, but if the compiler decides to re-read
  after that check, it can be true which can cause the code to crash
  later on.

- Make function profiler use the top level ops for filtering again

  When function graph became available for instances, its filter ops became
  independent from the top level set_ftrace_filter. In the process the
  function profiler received its own filter ops as well. But the function
  profiler uses the top level set_ftrace_filter file and does not have one
  of its own. In giving it its own filter ops, it lost any user interface
  it once had. Make it use the top level set_ftrace_filter file again.
  This fixes a regression.

[for-linus][PATCH 1/2] fgraph: Add READ_ONCE() when accessing fgraph_array[]

[Steven Rostedt]

From: Zilin Guan <zilin@seu.edu.cn>

In __ftrace_return_to_handler(), a loop iterates over the fgraph_array[]
elements, which are fgraph_ops. The loop checks if an element is a
fgraph_stub to prevent using a fgraph_stub afterward.

However, if the compiler reloads fgraph_array[] after this check, it might
race with an update to fgraph_array[] that introduces a fgraph_stub. This
could result in the stub being processed, but the stub contains a null
"func_hash" field, leading to a NULL pointer dereference.

To ensure that the gops compared against the fgraph_stub matches the gops
processed later, add a READ_ONCE(). A similar patch appears in commit
63a8dfb ("function_graph: Add READ_ONCE() when accessing fgraph_array[]").

Cc:stable@vger.kernel.org
Fixes: 37238abe3cb47 ("ftrace/function_graph: Pass fgraph_ops to function graph callbacks")
Link: https://lore.kernel.org/20241231113731.277668-1-zilin@seu.edu.cn
Signed-off-by: Zilin Guan <zilin@seu.edu.cn>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 kernel/trace/fgraph.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/trace/fgraph.c b/kernel/trace/fgraph.c
index ddedcb50917f..30e3ddc8a8a8 100644
--- a/kernel/trace/fgraph.c
+++ b/kernel/trace/fgraph.c
@@ -833,7 +833,7 @@ static unsigned long __ftrace_return_to_handler(struct fgraph_ret_regs *ret_regs
 #endif
 	{
 		for_each_set_bit(i, &bitmap, sizeof(bitmap) * BITS_PER_BYTE) {
-			struct fgraph_ops *gops = fgraph_array[i];
+			struct fgraph_ops *gops = READ_ONCE(fgraph_array[i]);
 
 			if (gops == &fgraph_stub)
 				continue;
-- 
2.45.2

[for-linus][PATCH 2/2] ftrace: Fix function profilers filtering functionality

[Steven Rostedt]

From: Kohei Enju <enjuk@amazon.com>

Commit c132be2c4fcc ("function_graph: Have the instances use their own
ftrace_ops for filtering"), function profiler (enabled via
function_profile_enabled) has been showing statistics for all functions,
ignoring set_ftrace_filter settings.

While tracers are instantiated, the function profiler is not. Therefore, it
should use the global set_ftrace_filter for consistency.  This patch
modifies the function profiler to use the global filter, fixing the
filtering functionality.

Before (filtering not working):
```
root@localhost:~# echo 'vfs*' > /sys/kernel/tracing/set_ftrace_filter
root@localhost:~# echo 1 > /sys/kernel/tracing/function_profile_enabled
root@localhost:~# sleep 1
root@localhost:~# echo 0 > /sys/kernel/tracing/function_profile_enabled
root@localhost:~# head /sys/kernel/tracing/trace_stat/*
  Function                               Hit    Time            Avg
     s^2
  --------                               ---    ----            ---
     ---
  schedule                               314    22290594 us     70989.15 us
     40372231 us
  x64_sys_call                          1527    8762510 us      5738.382 us
     3414354 us
  schedule_hrtimeout_range               176    8665356 us      49234.98 us
     405618876 us
  __x64_sys_ppoll                        324    5656635 us      17458.75 us
     19203976 us
  do_sys_poll                            324    5653747 us      17449.83 us
     19214945 us
  schedule_timeout                        67    5531396 us      82558.15 us
     2136740827 us
  __x64_sys_pselect6                      12    3029540 us      252461.7 us
     63296940171 us
  do_pselect.constprop.0                  12    3029532 us      252461.0 us
     63296952931 us
```

After (filtering working):
```
root@localhost:~# echo 'vfs*' > /sys/kernel/tracing/set_ftrace_filter
root@localhost:~# echo 1 > /sys/kernel/tracing/function_profile_enabled
root@localhost:~# sleep 1
root@localhost:~# echo 0 > /sys/kernel/tracing/function_profile_enabled
root@localhost:~# head /sys/kernel/tracing/trace_stat/*
  Function                               Hit    Time            Avg
     s^2
  --------                               ---    ----            ---
     ---
  vfs_write                              462    68476.43 us     148.217 us
     25874.48 us
  vfs_read                               641    9611.356 us     14.994 us
     28868.07 us
  vfs_fstat                              890    878.094 us      0.986 us
     1.667 us
  vfs_fstatat                            227    757.176 us      3.335 us
     18.928 us
  vfs_statx                              226    610.610 us      2.701 us
     17.749 us
  vfs_getattr_nosec                     1187    460.919 us      0.388 us
     0.326 us
  vfs_statx_path                         297    343.287 us      1.155 us
     11.116 us
  vfs_rename                               6    291.575 us      48.595 us
     9889.236 us
```

Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/20250101190820.72534-1-enjuk@amazon.com
Fixes: c132be2c4fcc ("function_graph: Have the instances use their own ftrace_ops for filtering")
Signed-off-by: Kohei Enju <enjuk@amazon.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 kernel/trace/ftrace.c | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 9b17efb1a87d..2e113f8b13a2 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -902,16 +902,13 @@ static void profile_graph_return(struct ftrace_graph_ret *trace,
 }
 
 static struct fgraph_ops fprofiler_ops = {
-	.ops = {
-		.flags = FTRACE_OPS_FL_INITIALIZED,
-		INIT_OPS_HASH(fprofiler_ops.ops)
-	},
 	.entryfunc = &profile_graph_entry,
 	.retfunc = &profile_graph_return,
 };
 
 static int register_ftrace_profiler(void)
 {
+	ftrace_ops_set_global_filter(&fprofiler_ops.ops);
 	return register_ftrace_graph(&fprofiler_ops);
 }
 
@@ -922,12 +919,11 @@ static void unregister_ftrace_profiler(void)
 #else
 static struct ftrace_ops ftrace_profile_ops __read_mostly = {
 	.func		= function_profile_call,
-	.flags		= FTRACE_OPS_FL_INITIALIZED,
-	INIT_OPS_HASH(ftrace_profile_ops)
 };
 
 static int register_ftrace_profiler(void)
 {
+	ftrace_ops_set_global_filter(&ftrace_profile_ops);
 	return register_ftrace_function(&ftrace_profile_ops);
 }
 
-- 
2.45.2