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authorSteven Rostedt <rostedt@goodmis.org>2008-08-27 09:14:40 -0400
committerLinus Torvalds <torvalds@linux-foundation.org>2008-08-27 13:54:20 -0700
commitf42ac38c59e0a03d6da0c24a63fb211393f484b0 (patch)
tree1020864d18c6652444fe0ba2d39dd6e9e2f3c7d6
parent8560c650f340565b720fd57d1f9c99ab216d99d0 (diff)
ftrace: disable tracing for suspend to ram
I've been painstakingly debugging the issue with suspend to ram and ftraced. The 2.6.28 code does not have this issue, but since the mcount recording is not going to be in 27, this must be solved for the ftrace daemon version. The resume from suspend to ram would reboot because it was triple faulting. Debugging further, I found that calling the mcount function itself was not an issue, but it would fault when it incremented preempt_count. preempt_count is on the tasks info structure that is on the low memory address of the task's stack. For some reason, it could not write to it. Resuming out of suspend to ram does quite a lot of funny tricks to get to work, so it is not surprising at all that simply doing a preempt_disable() would cause a fault. Thanks to Rafael for suggesting to add a "while (1);" to find the place in resuming that is causing the fault. I would place the loop somewhere in the code, compile and reboot and see if it would either reboot (hit the fault) or simply hang (hit the loop). Doing this over and over again, I narrowed it down that it was happening in enable_nonboot_cpus. At this point, I found that it is easier to simply disable tracing around the suspend code, instead of searching for the particular function that can not handle doing a preempt_disable. This patch disables the tracer as it suspends and reenables it on resume. I tested this patch on my Laptop, and it can resume fine with the patch. Signed-off-by: Steven Rostedt <srostedt@redhat.com> Acked-by: Rafael J. Wysocki <rjw@sisk.pl> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--kernel/power/main.c5
1 files changed, 4 insertions, 1 deletions
diff --git a/kernel/power/main.c b/kernel/power/main.c
index 0b7476f5d2a6..540b16b68565 100644
--- a/kernel/power/main.c
+++ b/kernel/power/main.c
@@ -21,6 +21,7 @@
#include <linux/freezer.h>
#include <linux/vmstat.h>
#include <linux/syscalls.h>
+#include <linux/ftrace.h>
#include "power.h"
@@ -310,7 +311,7 @@ static int suspend_enter(suspend_state_t state)
*/
int suspend_devices_and_enter(suspend_state_t state)
{
- int error;
+ int error, ftrace_save;
if (!suspend_ops)
return -ENOSYS;
@@ -321,6 +322,7 @@ int suspend_devices_and_enter(suspend_state_t state)
goto Close;
}
suspend_console();
+ ftrace_save = __ftrace_enabled_save();
suspend_test_start();
error = device_suspend(PMSG_SUSPEND);
if (error) {
@@ -352,6 +354,7 @@ int suspend_devices_and_enter(suspend_state_t state)
suspend_test_start();
device_resume(PMSG_RESUME);
suspend_test_finish("resume devices");
+ __ftrace_enabled_restore(ftrace_save);
resume_console();
Close:
if (suspend_ops->end)

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