This is a note to let you know that I've just added the patch titled
tracing: Try again for saved cmdline if failed due to locking
to the 3.15-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-try-again-for-saved-cmdline-if-failed-due-to-locking.patch
and it can be found in the queue-3.15 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 379cfdac37923653c9d4242d10052378b7563005 Mon Sep 17 00:00:00 2001
From: "Steven Rostedt (Red Hat)" <rostedt@xxxxxxxxxxx>
Date: Fri, 30 May 2014 09:42:39 -0400
Subject: tracing: Try again for saved cmdline if failed due to locking
From: "Steven Rostedt (Red Hat)" <rostedt@xxxxxxxxxxx>
commit 379cfdac37923653c9d4242d10052378b7563005 upstream.
In order to prevent the saved cmdline cache from being filled when
tracing is not active, the comms are only recorded after a trace event
is recorded.
The problem is, a comm can fail to be recorded if the trace_cmdline_lock
is held. That lock is taken via a trylock to allow it to happen from
any context (including NMI). If the lock fails to be taken, the comm
is skipped. No big deal, as we will try again later.
But! Because of the code that was added to only record after an event,
we may not try again later as the recording is made as a oneshot per
event per CPU.
Only disable the recording of the comm if the comm is actually recorded.
Fixes: 7ffbd48d5cab "tracing: Cache comms only after an event occurred"
Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
kernel/trace/trace.c | 13 +++++++------
1 file changed, 7 insertions(+), 6 deletions(-)
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -1461,12 +1461,12 @@ static void tracing_stop_tr(struct trace
void trace_stop_cmdline_recording(void);
-static void trace_save_cmdline(struct task_struct *tsk)
+static int trace_save_cmdline(struct task_struct *tsk)
{
unsigned pid, idx;
if (!tsk->pid || unlikely(tsk->pid > PID_MAX_DEFAULT))
- return;
+ return 0;
/*
* It's not the end of the world if we don't get
@@ -1475,7 +1475,7 @@ static void trace_save_cmdline(struct ta
* so if we miss here, then better luck next time.
*/
if (!arch_spin_trylock(&trace_cmdline_lock))
- return;
+ return 0;
idx = map_pid_to_cmdline[tsk->pid];
if (idx == NO_CMDLINE_MAP) {
@@ -1500,6 +1500,8 @@ static void trace_save_cmdline(struct ta
memcpy(&saved_cmdlines[idx], tsk->comm, TASK_COMM_LEN);
arch_spin_unlock(&trace_cmdline_lock);
+
+ return 1;
}
void trace_find_cmdline(int pid, char comm[])
@@ -1541,9 +1543,8 @@ void tracing_record_cmdline(struct task_
if (!__this_cpu_read(trace_cmdline_save))
return;
- __this_cpu_write(trace_cmdline_save, false);
-
- trace_save_cmdline(tsk);
+ if (trace_save_cmdline(tsk))
+ __this_cpu_write(trace_cmdline_save, false);
}
void
Patches currently in stable-queue which might be from rostedt@xxxxxxxxxxx are
queue-3.15/tracing-fix-syscall_-regfunc-vs-copy_process-race.patch
queue-3.15/tracing-try-again-for-saved-cmdline-if-failed-due-to-locking.patch
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