sched: Set the command name of the idle tasks in SMP kernels

In UP systems, the idle task is initialized using the init_task
structure from which the command name is taken (currently "swapper").

In SMP systems, one idle task per CPU is forked by the worker thread
from which the task structure is copied. The command name is, therefore,
"kworker/0:0" or "kworker/0:1", if not updated. Since such update was
lacking, all idle tasks in SMP systems were incorrectly named. This
longtime bug was not discovered immediately, because there is no /proc/0
entry - the bug only becomes apparent when tracing is enabled.

This patch sets the command name of the idle tasks in SMP systems to the
name that is used in the INIT_TASK structure suffixed by a slash and the
number of the CPU.

Signed-off-by: Carsten Emde <C.Emde@osadl.org>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/20111026211708.768925506@osadl.org
Signed-off-by: Ingo Molnar <mingo@elte.hu>

2 files changed, 7 insertions, 1 deletions

diff --git a/include/linux/init_task.h b/include/linux/init_task.h
index 08ffab01e76c..b6e5b8b000e0 100644
--- a/include/linux/init_task.h
+++ b/include/linux/init_task.h
@@ -126,6 +126,8 @@ extern struct cred init_cred;
 # define INIT_PERF_EVENTS(tsk)
 #endif
 
+#define INIT_TASK_COMM "swapper"
+
 /*
  *  INIT_TASK is used to set up the first task table, touch at
  * your own risk!. Base=0, limit=0x1fffff (=2MB)
@@ -162,7 +164,7 @@ extern struct cred init_cred;
         .group_leader   = &tsk,                                         \
         RCU_INIT_POINTER(.real_cred, &init_cred),                       \
         RCU_INIT_POINTER(.cred, &init_cred),                            \
-        .comm           = "swapper",                                    \
+        .comm           = INIT_TASK_COMM,                               \
         .thread         = INIT_THREAD,                                  \
         .fs             = &init_fs,                                     \
         .files          = &init_files,                                  \
diff --git a/kernel/sched.c b/kernel/sched.c
index 3d2c436959a1..d6b149ccf925 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -71,6 +71,7 @@
 #include <linux/ctype.h>
 #include <linux/ftrace.h>
 #include <linux/slab.h>
+#include <linux/init_task.h>
 
 #include <asm/tlb.h>
 #include <asm/irq_regs.h>
@@ -6112,6 +6113,9 @@ void __cpuinit init_idle(struct task_struct *idle, int cpu)
          */
         idle->sched_class = &idle_sched_class;
         ftrace_graph_init_idle_task(idle, cpu);
+#if defined(CONFIG_SMP)
+        sprintf(idle->comm, "%s/%d", INIT_TASK_COMM, cpu);
+#endif
 }
 
 /*