introduce PF_KTHREAD flag

Introduce the new PF_KTHREAD flag to mark the kernel threads.  It is set
by INIT_TASK() and copied to the forked childs (we could set it in
kthreadd() along with PF_NOFREEZE instead).

daemonize() was changed as well.  In that case testing of PF_KTHREAD is
racy, but daemonize() is hopeless anyway.

This flag is cleared in do_execve(), before search_binary_handler().
Probably not the best place, we can do this in exec_mmap() or in
start_thread(), or clear it along with PF_FORKNOEXEC.  But I think this
doesn't matter in practice, and if do_execve() fails kthread should die
soon.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Roland McGrath <roland@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 2 insertions, 1 deletions

diff --git a/include/linux/init_task.h b/include/linux/init_task.h
index 93c45acf249..021d8e720c7 100644
--- a/include/linux/init_task.h
+++ b/include/linux/init_task.h
@@ -122,7 +122,7 @@ extern struct group_info init_groups;
         .state          = 0,                                            \
         .stack          = &init_thread_info,                            \
         .usage          = ATOMIC_INIT(2),                               \
-        .flags          = 0,                                            \
+        .flags          = PF_KTHREAD,                                   \
         .lock_depth     = -1,                                           \
         .prio           = MAX_PRIO-20,                                  \
         .static_prio    = MAX_PRIO-20,                                  \
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 79e749dbf81..eec64a4adb9 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1483,6 +1483,7 @@ static inline void put_task_struct(struct task_struct *t)
 #define PF_EXITING      0x00000004      /* getting shut down */
 #define PF_EXITPIDONE   0x00000008      /* pi exit done on shut down */
 #define PF_VCPU         0x00000010      /* I'm a virtual CPU */
+#define PF_KTHREAD      0x00000020      /* I am a kernel thread */
 #define PF_FORKNOEXEC   0x00000040      /* forked but didn't exec */
 #define PF_SUPERPRIV    0x00000100      /* used super-user privileges */
 #define PF_DUMPCORE     0x00000200      /* dumped core */