[PATCH] change current_is_single_threaded() to use for_each_thread()

[PATCH] change current_is_single_threaded() to use for_each_thread()

[Oleg Nesterov]

Change current_is_single_threaded() to use for_each_thread() rather
than deprecated while_each_thread().

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
 lib/is_single_threaded.c |    5 ++---
 1 files changed, 2 insertions(+), 3 deletions(-)

diff --git a/lib/is_single_threaded.c b/lib/is_single_threaded.c
index bd2bea9..391fd23 100644
--- a/lib/is_single_threaded.c
+++ b/lib/is_single_threaded.c
@@ -36,8 +36,7 @@ bool current_is_single_threaded(void)
 		if (unlikely(p == task->group_leader))
 			continue;
 
-		t = p;
-		do {
+		for_each_thread(p, t) {
 			if (unlikely(t->mm == mm))
 				goto found;
 			if (likely(t->mm))
@@ -48,7 +47,7 @@ bool current_is_single_threaded(void)
 			 * forked before exiting.
 			 */
 			smp_rmb();
-		} while_each_thread(p, t);
+		}
 	}
 	ret = true;
 found:
-- 
1.5.5.1

Re: [PATCH] change current_is_single_threaded() to use for_each_thread()

[David Howells]

Oleg Nesterov <oleg@redhat.com> wrote:

> Change current_is_single_threaded() to use for_each_thread() rather
> than deprecated while_each_thread().

Wouldn't the old way be more efficient, given there's always going to be at
least one thread?  Granted, it's not much of an efficiency boost...

David

Re: [PATCH] change current_is_single_threaded() to use for_each_thread()

[Oleg Nesterov]

On 10/07, David Howells wrote:
>
> Oleg Nesterov <oleg@redhat.com> wrote:
>
> > Change current_is_single_threaded() to use for_each_thread() rather
> > than deprecated while_each_thread().
>
> Wouldn't the old way be more efficient, given there's always going to be at
> least one thread?

Yes, unfortunately. Before this change (in the likely case) we never
do next_thread(), after this patch we always do list_first_entry().

> Granted, it's not much of an efficiency boost...

Yes, and while_each_thread() is buggy. See the changelog in 0c740d0afc
"introduce for_each_thread() to replace the buggy while_each_thread().

Yes, the race is almost purely theoretical, but still.

To clarify, we had some "real" bugs fixed by s/while_each_thread/
for_each_thread/, but only because while_each_thread() was used wrongly.
for_each_thread() is more safe, it only needs the stable task_struct.

Oleg.

Re: [PATCH] change current_is_single_threaded() to use for_each_thread()

[David Howells]

Oleg Nesterov <oleg@redhat.com> wrote:

> To clarify, we had some "real" bugs fixed by s/while_each_thread/
> for_each_thread/, but only because while_each_thread() was used wrongly.
> for_each_thread() is more safe, it only needs the stable task_struct.

Fair enough.

David