[PATCH] ptrace: cleanup ptrace_init_task()->ptrace_link() path

[PATCH] ptrace: cleanup ptrace_init_task()->ptrace_link() path

[Oleg Nesterov]

No functional changes.

ptrace_init_task() looks confusing, as if we always auto-attach when
"bool ptrace" argument is true, while in fact we attach only if current
is traced.

Make the code more explicit and kill now unused ptrace_link().

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Roland McGrath <roland@redhat.com>
---

 include/linux/ptrace.h |   11 +++--------
 1 file changed, 3 insertions(+), 8 deletions(-)

--- V1/include/linux/ptrace.h~1_PTRACE_INIT_TASK	2009-10-30 00:44:22.000000000 +0100
+++ V1/include/linux/ptrace.h	2009-10-30 00:46:06.000000000 +0100
@@ -105,12 +105,7 @@ static inline int ptrace_reparented(stru
 {
 	return child->real_parent != child->parent;
 }
-static inline void ptrace_link(struct task_struct *child,
-			       struct task_struct *new_parent)
-{
-	if (unlikely(child->ptrace))
-		__ptrace_link(child, new_parent);
-}
+
 static inline void ptrace_unlink(struct task_struct *child)
 {
 	if (unlikely(child->ptrace))
@@ -169,9 +164,9 @@ static inline void ptrace_init_task(stru
 	INIT_LIST_HEAD(&child->ptraced);
 	child->parent = child->real_parent;
 	child->ptrace = 0;
-	if (unlikely(ptrace)) {
+	if (unlikely(ptrace) && (current->ptrace & PT_PTRACED)) {
 		child->ptrace = current->ptrace;
-		ptrace_link(child, current->parent);
+		__ptrace_link(child, current->parent);
 	}
 }
 

Re: [PATCH] ptrace: cleanup ptrace_init_task()->ptrace_link() path

[Andrew Morton]

On Fri, 30 Oct 2009 00:56:56 +0100
Oleg Nesterov <oleg@redhat.com> wrote:

>  ptrace

Speaking of which, I'm still sitting on
do_wait-optimization-do-not-place-sub-threads-on-task_struct-children-list.patch.
Should I drop it?



From: Oleg Nesterov <oleg@redhat.com>

Thanks to Roland who pointed out de_thread() issues.

Currently we add sub-threads to ->real_parent->children list.  This buys
nothing but slows down do_wait().

With this patch ->children contains only main threads (group leaders). 
The only complication is that forget_original_parent() should iterate over
sub-threads by hand, and de_thread() needs another list_replace() when it
changes ->group_leader.

Henceforth do_wait_thread() can never see task_detached() && !EXIT_DEAD
tasks, we can remove this check (and we can unify do_wait_thread() and
ptrace_do_wait()).

This change can confuse the optimistic search in mm_update_next_owner(),
but this is fixable and minor.

Perhaps badness() and oom_kill_process() should be updated, but they
should be fixed in any case.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: Roland McGrath <roland@redhat.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Ratan Nalumasu <rnalumasu@gmail.com>
Cc: Vitaly Mayatskikh <vmayatsk@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 fs/exec.c     |    2 ++
 kernel/exit.c |   36 +++++++++++++++++-------------------
 kernel/fork.c |    2 +-
 3 files changed, 20 insertions(+), 20 deletions(-)

diff -puN fs/exec.c~do_wait-optimization-do-not-place-sub-threads-on-task_struct-children-list fs/exec.c
--- a/fs/exec.c~do_wait-optimization-do-not-place-sub-threads-on-task_struct-children-list
+++ a/fs/exec.c
@@ -829,7 +829,9 @@ static int de_thread(struct task_struct 
 		attach_pid(tsk, PIDTYPE_PID,  task_pid(leader));
 		transfer_pid(leader, tsk, PIDTYPE_PGID);
 		transfer_pid(leader, tsk, PIDTYPE_SID);
+
 		list_replace_rcu(&leader->tasks, &tsk->tasks);
+		list_replace_init(&leader->sibling, &tsk->sibling);
 
 		tsk->group_leader = tsk;
 		leader->group_leader = tsk;
diff -puN kernel/exit.c~do_wait-optimization-do-not-place-sub-threads-on-task_struct-children-list kernel/exit.c
--- a/kernel/exit.c~do_wait-optimization-do-not-place-sub-threads-on-task_struct-children-list
+++ a/kernel/exit.c
@@ -67,10 +67,10 @@ static void __unhash_process(struct task
 		detach_pid(p, PIDTYPE_SID);
 
 		list_del_rcu(&p->tasks);
+		list_del_init(&p->sibling);
 		__get_cpu_var(process_counts)--;
 	}
 	list_del_rcu(&p->thread_group);
-	list_del_init(&p->sibling);
 }
 
 /*
@@ -737,12 +737,9 @@ static struct task_struct *find_new_reap
 /*
 * Any that need to be release_task'd are put on the @dead list.
  */
-static void reparent_thread(struct task_struct *father, struct task_struct *p,
+static void reparent_leader(struct task_struct *father, struct task_struct *p,
 				struct list_head *dead)
 {
-	if (p->pdeath_signal)
-		group_send_sig_info(p->pdeath_signal, SEND_SIG_NOINFO, p);
-
 	list_move_tail(&p->sibling, &p->real_parent->children);
 
 	if (task_detached(p))
@@ -781,12 +778,18 @@ static void forget_original_parent(struc
 	reaper = find_new_reaper(father);
 
 	list_for_each_entry_safe(p, n, &father->children, sibling) {
-		p->real_parent = reaper;
-		if (p->parent == father) {
-			BUG_ON(task_ptrace(p));
-			p->parent = p->real_parent;
-		}
-		reparent_thread(father, p, &dead_children);
+		struct task_struct *t = p;
+		do {
+			t->real_parent = reaper;
+			if (t->parent == father) {
+				BUG_ON(task_ptrace(t));
+				t->parent = t->real_parent;
+			}
+			if (t->pdeath_signal)
+				group_send_sig_info(t->pdeath_signal,
+						    SEND_SIG_NOINFO, t);
+		} while_each_thread(p, t);
+		reparent_leader(father, p, &dead_children);
 	}
 	write_unlock_irq(&tasklist_lock);
 
@@ -1546,14 +1549,9 @@ static int do_wait_thread(struct wait_op
 	struct task_struct *p;
 
 	list_for_each_entry(p, &tsk->children, sibling) {
-		/*
-		 * Do not consider detached threads.
-		 */
-		if (!task_detached(p)) {
-			int ret = wait_consider_task(wo, 0, p);
-			if (ret)
-				return ret;
-		}
+		int ret = wait_consider_task(wo, 0, p);
+		if (ret)
+			return ret;
 	}
 
 	return 0;
diff -puN kernel/fork.c~do_wait-optimization-do-not-place-sub-threads-on-task_struct-children-list kernel/fork.c
--- a/kernel/fork.c~do_wait-optimization-do-not-place-sub-threads-on-task_struct-children-list
+++ a/kernel/fork.c
@@ -1273,7 +1273,6 @@ static struct task_struct *copy_process(
 	}
 
 	if (likely(p->pid)) {
-		list_add_tail(&p->sibling, &p->real_parent->children);
 		tracehook_finish_clone(p, clone_flags, trace);
 
 		if (thread_group_leader(p)) {
@@ -1285,6 +1284,7 @@ static struct task_struct *copy_process(
 			p->signal->tty = tty_kref_get(current->signal->tty);
 			attach_pid(p, PIDTYPE_PGID, task_pgrp(current));
 			attach_pid(p, PIDTYPE_SID, task_session(current));
+			list_add_tail(&p->sibling, &p->real_parent->children);
 			list_add_tail_rcu(&p->tasks, &init_task.tasks);
 			__get_cpu_var(process_counts)++;
 		}
_

Re: [PATCH] ptrace: cleanup ptrace_init_task()->ptrace_link() path

[Oleg Nesterov]

On 10/30, Andrew Morton wrote:
>
> On Fri, 30 Oct 2009 00:56:56 +0100
> Oleg Nesterov <oleg@redhat.com> wrote:
>
> >  ptrace
>
> Speaking of which, I'm still sitting on
> do_wait-optimization-do-not-place-sub-threads-on-task_struct-children-list.patch.

(this patch has nothing to do with ptrace)

> Should I drop it?

Why? I think this is good optimization and imho cleanup.

There is no point to have sub-thread in ->children list and this
slows down do_wait() if a child has a lot of threads, it has to
iterate over all sub-threads just to filter them out.

Oleg.

> From: Oleg Nesterov <oleg@redhat.com>
>
> Thanks to Roland who pointed out de_thread() issues.
>
> Currently we add sub-threads to ->real_parent->children list.  This buys
> nothing but slows down do_wait().
>
> With this patch ->children contains only main threads (group leaders).
> The only complication is that forget_original_parent() should iterate over
> sub-threads by hand, and de_thread() needs another list_replace() when it
> changes ->group_leader.
>
> Henceforth do_wait_thread() can never see task_detached() && !EXIT_DEAD
> tasks, we can remove this check (and we can unify do_wait_thread() and
> ptrace_do_wait()).
>
> This change can confuse the optimistic search in mm_update_next_owner(),
> but this is fixable and minor.
>
> Perhaps badness() and oom_kill_process() should be updated, but they
> should be fixed in any case.
>
> Signed-off-by: Oleg Nesterov <oleg@redhat.com>
> Cc: Roland McGrath <roland@redhat.com>
> Cc: Ingo Molnar <mingo@elte.hu>
> Cc: Ratan Nalumasu <rnalumasu@gmail.com>
> Cc: Vitaly Mayatskikh <vmayatsk@redhat.com>
> Cc: David Rientjes <rientjes@google.com>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> ---
>
>  fs/exec.c     |    2 ++
>  kernel/exit.c |   36 +++++++++++++++++-------------------
>  kernel/fork.c |    2 +-
>  3 files changed, 20 insertions(+), 20 deletions(-)
>
> diff -puN fs/exec.c~do_wait-optimization-do-not-place-sub-threads-on-task_struct-children-list fs/exec.c
> --- a/fs/exec.c~do_wait-optimization-do-not-place-sub-threads-on-task_struct-children-list
> +++ a/fs/exec.c
> @@ -829,7 +829,9 @@ static int de_thread(struct task_struct
>  		attach_pid(tsk, PIDTYPE_PID,  task_pid(leader));
>  		transfer_pid(leader, tsk, PIDTYPE_PGID);
>  		transfer_pid(leader, tsk, PIDTYPE_SID);
> +
>  		list_replace_rcu(&leader->tasks, &tsk->tasks);
> +		list_replace_init(&leader->sibling, &tsk->sibling);
>
>  		tsk->group_leader = tsk;
>  		leader->group_leader = tsk;
> diff -puN kernel/exit.c~do_wait-optimization-do-not-place-sub-threads-on-task_struct-children-list kernel/exit.c
> --- a/kernel/exit.c~do_wait-optimization-do-not-place-sub-threads-on-task_struct-children-list
> +++ a/kernel/exit.c
> @@ -67,10 +67,10 @@ static void __unhash_process(struct task
>  		detach_pid(p, PIDTYPE_SID);
>
>  		list_del_rcu(&p->tasks);
> +		list_del_init(&p->sibling);
>  		__get_cpu_var(process_counts)--;
>  	}
>  	list_del_rcu(&p->thread_group);
> -	list_del_init(&p->sibling);
>  }
>
>  /*
> @@ -737,12 +737,9 @@ static struct task_struct *find_new_reap
>  /*
>  * Any that need to be release_task'd are put on the @dead list.
>   */
> -static void reparent_thread(struct task_struct *father, struct task_struct *p,
> +static void reparent_leader(struct task_struct *father, struct task_struct *p,
>  				struct list_head *dead)
>  {
> -	if (p->pdeath_signal)
> -		group_send_sig_info(p->pdeath_signal, SEND_SIG_NOINFO, p);
> -
>  	list_move_tail(&p->sibling, &p->real_parent->children);
>
>  	if (task_detached(p))
> @@ -781,12 +778,18 @@ static void forget_original_parent(struc
>  	reaper = find_new_reaper(father);
>
>  	list_for_each_entry_safe(p, n, &father->children, sibling) {
> -		p->real_parent = reaper;
> -		if (p->parent == father) {
> -			BUG_ON(task_ptrace(p));
> -			p->parent = p->real_parent;
> -		}
> -		reparent_thread(father, p, &dead_children);
> +		struct task_struct *t = p;
> +		do {
> +			t->real_parent = reaper;
> +			if (t->parent == father) {
> +				BUG_ON(task_ptrace(t));
> +				t->parent = t->real_parent;
> +			}
> +			if (t->pdeath_signal)
> +				group_send_sig_info(t->pdeath_signal,
> +						    SEND_SIG_NOINFO, t);
> +		} while_each_thread(p, t);
> +		reparent_leader(father, p, &dead_children);
>  	}
>  	write_unlock_irq(&tasklist_lock);
>
> @@ -1546,14 +1549,9 @@ static int do_wait_thread(struct wait_op
>  	struct task_struct *p;
>
>  	list_for_each_entry(p, &tsk->children, sibling) {
> -		/*
> -		 * Do not consider detached threads.
> -		 */
> -		if (!task_detached(p)) {
> -			int ret = wait_consider_task(wo, 0, p);
> -			if (ret)
> -				return ret;
> -		}
> +		int ret = wait_consider_task(wo, 0, p);
> +		if (ret)
> +			return ret;
>  	}
>
>  	return 0;
> diff -puN kernel/fork.c~do_wait-optimization-do-not-place-sub-threads-on-task_struct-children-list kernel/fork.c
> --- a/kernel/fork.c~do_wait-optimization-do-not-place-sub-threads-on-task_struct-children-list
> +++ a/kernel/fork.c
> @@ -1273,7 +1273,6 @@ static struct task_struct *copy_process(
>  	}
>
>  	if (likely(p->pid)) {
> -		list_add_tail(&p->sibling, &p->real_parent->children);
>  		tracehook_finish_clone(p, clone_flags, trace);
>
>  		if (thread_group_leader(p)) {
> @@ -1285,6 +1284,7 @@ static struct task_struct *copy_process(
>  			p->signal->tty = tty_kref_get(current->signal->tty);
>  			attach_pid(p, PIDTYPE_PGID, task_pgrp(current));
>  			attach_pid(p, PIDTYPE_SID, task_session(current));
> +			list_add_tail(&p->sibling, &p->real_parent->children);
>  			list_add_tail_rcu(&p->tasks, &init_task.tasks);
>  			__get_cpu_var(process_counts)++;
>  		}
> _
>

Re: [PATCH] ptrace: cleanup ptrace_init_task()->ptrace_link() path

[Andrew Morton]

On Sat, 31 Oct 2009 01:55:07 +0100 Oleg Nesterov <oleg@redhat.com> wrote:

> On 10/30, Andrew Morton wrote:
> >
> > On Fri, 30 Oct 2009 00:56:56 +0100
> > Oleg Nesterov <oleg@redhat.com> wrote:
> >
> > >  ptrace
> >
> > Speaking of which, I'm still sitting on
> > do_wait-optimization-do-not-place-sub-threads-on-task_struct-children-list.patch.
> 
> (this patch has nothing to do with ptrace)
> 
> > Should I drop it?
> 
> Why? I think this is good optimization and imho cleanup.
> 
> There is no point to have sub-thread in ->children list and this
> slows down do_wait() if a child has a lot of threads, it has to
> iterate over all sub-threads just to filter them out.
> 

On 17 Sep you said:

: Yes, risky... God knows who can do list_for_each(->children) and expect to
: find the sub-threads. But this is obviously good optimization/simplification.
:
: It is just ugly to place sub-threads on ->children list, this buys nothing
: but slown downs do_wait(). (this was needed, afaics, to handle ptraced but
: not re-parented threads a long ago).

so that's why I didn't merge it into 2.6.32.  Is the patch still
considered "risky"?

Re: [PATCH] ptrace: cleanup ptrace_init_task()->ptrace_link() path

[Oleg Nesterov]

On 10/30, Andrew Morton wrote:
>
> On Sat, 31 Oct 2009 01:55:07 +0100 Oleg Nesterov <oleg@redhat.com> wrote:
>
> > On 10/30, Andrew Morton wrote:
> > >
> > > On Fri, 30 Oct 2009 00:56:56 +0100
> > > Oleg Nesterov <oleg@redhat.com> wrote:
> > >
> > > >  ptrace
> > >
> > > Speaking of which, I'm still sitting on
> > > do_wait-optimization-do-not-place-sub-threads-on-task_struct-children-list.patch.
> >
> > (this patch has nothing to do with ptrace)
> >
> > > Should I drop it?
> >
> > Why? I think this is good optimization and imho cleanup.
> >
> > There is no point to have sub-thread in ->children list and this
> > slows down do_wait() if a child has a lot of threads, it has to
> > iterate over all sub-threads just to filter them out.
> >
>
> On 17 Sep you said:
>
> : Yes, risky... God knows who can do list_for_each(->children) and expect to
> : find the sub-threads. But this is obviously good optimization/simplification.
> :
> : It is just ugly to place sub-threads on ->children list, this buys nothing
> : but slown downs do_wait(). (this was needed, afaics, to handle ptraced but
> : not re-parented threads a long ago).
>
> so that's why I didn't merge it into 2.6.32.  Is the patch still
> considered "risky"?

I hope not, it didn't cause any problems during 3 months in -mm.

Oleg.