Re: [PATCH 1/3] introduce PF_KTHREAD flag

[Andrew Morton <akpm@linux-foundation.org>]

On Mon, 23 Jun 2008 13:40:37 -0700
Andrew Morton <akpm@linux-foundation.org> wrote:

> On Sun, 1 Jun 2008 19:30:42 +0400
> Oleg Nesterov <oleg@tv-sign.ru> wrote:
> 
> > 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 */
> 
> Well "Freezer: Introduce PF_FREEZER_NOSIG" has cheerily come in
> afterwards and stolen 0x80000000 from us.  I'll redo this patch to use,
> umm, 0x00000020.  Please check that this is OK (if it isn't someone
> needs thwapping for not adding a dont-use-this comment).
> 

OK, it seems that in a later patch we switched to 0x00200000 anyway.

"Freezer: Introduce PF_FREEZER_NOSIG" has trashed this patch
series so I'll need to drop introduce-pf_kthread-flag.patch and
kill-pf_borrowed_mm-in-favour-of-pf_kthread.patch and
coredump-zap_threads-must-skip-kernel-threads.patch.

I don't yet know how much additional damage will happen as a result.