[PATCH 3.18 44/97] ftrace: Fix ftrace enable ordering of sysctl ftrace_enabled

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



From: "Steven Rostedt (Red Hat)" <rostedt@xxxxxxxxxxx>

[ Upstream commit 524a38682573b2e15ab6317ccfe50280441514be ]

Some archs (specifically PowerPC), are sensitive with the ordering of
the enabling of the calls to function tracing and setting of the
function to use to be traced.

That is, update_ftrace_function() sets what function the ftrace_caller
trampoline should call. Some archs require this to be set before
calling ftrace_run_update_code().

Another bug was discovered, that ftrace_startup_sysctl() called
ftrace_run_update_code() directly. If the function the ftrace_caller
trampoline changes, then it will not be updated. Instead a call
to ftrace_startup_enable() should be called because it tests to see
if the callback changed since the code was disabled, and will
tell the arch to update appropriately. Most archs do not need this
notification, but PowerPC does.

The problem could be seen by the following commands:

 # echo 0 > /proc/sys/kernel/ftrace_enabled
 # echo function > /sys/kernel/debug/tracing/current_tracer
 # echo 1 > /proc/sys/kernel/ftrace_enabled
 # cat /sys/kernel/debug/tracing/trace

The trace will show that function tracing was not active.

Cc: stable@xxxxxxxxxxxxxxx # 2.6.27+
Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
Signed-off-by: Sasha Levin <sasha.levin@xxxxxxxxxx>
---
 kernel/trace/ftrace.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index d977c72..d1eff3d 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -2504,7 +2504,7 @@ static void ftrace_startup_sysctl(void)
 		command = FTRACE_UPDATE_CALLS;
 		if (ftrace_graph_active)
 			command |= FTRACE_START_FUNC_RET;
-		ftrace_run_update_code(command);
+		ftrace_startup_enable(command);
 	}
 }
 
@@ -5325,12 +5325,12 @@ ftrace_enable_sysctl(struct ctl_table *table, int write,
 
 	if (ftrace_enabled) {
 
-		ftrace_startup_sysctl();
-
 		/* we are starting ftrace again */
 		if (ftrace_ops_list != &ftrace_list_end)
 			update_ftrace_function();
 
+		ftrace_startup_sysctl();
+
 	} else {
 		/* stopping ftrace calls (just send to ftrace_stub) */
 		ftrace_trace_function = ftrace_stub;
-- 
2.1.0

--
To unsubscribe from this list: send the line "unsubscribe stable" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html




[Index of Archives]     [Linux Kernel]     [Kernel Development Newbies]     [Linux USB Devel]     [Video for Linux]     [Linux Audio Users]     [Yosemite Hiking]     [Linux Kernel]     [Linux SCSI]