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Subject[PATCH 1/3] 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>

include/linux/sched.h | 1 +
include/linux/init_task.h | 2 +-
kernel/exit.c | 2 +-
fs/exec.c | 1 +
4 files changed, 4 insertions(+), 2 deletions(-)

--- 26-rc2/include/linux/sched.h~2_MAKE_PF_KTHREAD 2008-05-18 15:44:16.000000000 +0400
+++ 26-rc2/include/linux/sched.h 2008-05-18 20:08:13.000000000 +0400
@@ -1508,6 +1508,7 @@ static inline void put_task_struct(struc
#define PF_MEMPOLICY 0x10000000 /* Non-default NUMA mempolicy */
#define PF_MUTEX_TESTER 0x20000000 /* Thread belongs to the rt mutex tester */
#define PF_FREEZER_SKIP 0x40000000 /* Freezer should not count it as freezeable */
+#define PF_KTHREAD 0x80000000 /* I am a kernel thread */

/*
* Only the _current_ task can read/write to tsk->flags, but other
--- 26-rc2/include/linux/init_task.h~2_MAKE_PF_KTHREAD 2008-05-18 15:44:15.000000000 +0400
+++ 26-rc2/include/linux/init_task.h 2008-05-18 20:14:30.000000000 +0400
@@ -143,7 +143,7 @@ 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, \
--- 26-rc2/kernel/exit.c~2_MAKE_PF_KTHREAD 2008-05-18 15:44:18.000000000 +0400
+++ 26-rc2/kernel/exit.c 2008-05-18 18:11:13.000000000 +0400
@@ -416,7 +416,7 @@ void daemonize(const char *name, ...)
* We don't want to have TIF_FREEZE set if the system-wide hibernation
* or suspend transition begins right now.
*/
- current->flags |= PF_NOFREEZE;
+ current->flags |= (PF_NOFREEZE | PF_KTHREAD);

if (current->nsproxy != &init_nsproxy) {
get_nsproxy(&init_nsproxy);
--- 26-rc2/fs/exec.c~2_MAKE_PF_KTHREAD 2008-05-18 15:44:00.000000000 +0400
+++ 26-rc2/fs/exec.c 2008-05-18 18:36:30.000000000 +0400
@@ -1317,6 +1317,7 @@ int do_execve(char * filename,
if (retval < 0)
goto out;

+ current->flags &= ~PF_KTHREAD;
retval = search_binary_handler(bprm,regs);
if (retval >= 0) {
/* execve success */


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