* Re: [PATCH] jump_label_inc may return before the code is patched
2011-10-18 17:55 [PATCH] jump_label_inc may return before the code is patched Gleb Natapov
@ 2011-10-18 20:54 ` Jason Baron
2011-10-19 7:03 ` Gleb Natapov
2011-10-18 21:06 ` Steven Rostedt
` (2 subsequent siblings)
3 siblings, 1 reply; 8+ messages in thread
From: Jason Baron @ 2011-10-18 20:54 UTC (permalink / raw)
To: Gleb Natapov; +Cc: linux-kernel, Peter Zijlstra, Steven Rostedt
On Tue, Oct 18, 2011 at 07:55:51PM +0200, Gleb Natapov wrote:
> If cpu A calls jump_label_inc() just after atomic_add_return() is
> called by cpu B, atomic_inc_not_zero() will return value greater then
> zero and jump_label_inc() will return to a caller before jump_label_update()
> finishes its job on cpu B.
>
> Signed-off-by: Gleb Natapov <gleb@redhat.com>
> diff --git a/kernel/jump_label.c b/kernel/jump_label.c
> index a8ce450..e6f1f24 100644
> --- a/kernel/jump_label.c
> +++ b/kernel/jump_label.c
> @@ -66,8 +66,9 @@ void jump_label_inc(struct jump_label_key *key)
> return;
>
> jump_label_lock();
> - if (atomic_add_return(1, &key->enabled) == 1)
> + if (atomic_read(&key->enabled) == 0)
> jump_label_update(key, JUMP_LABEL_ENABLE);
> + atomic_inc(&key->enabled);
> jump_label_unlock();
> }
>
agreed, we shouldn't return before the update happens...did this cause any
actual problem in practice? Or just observed from code inspection?
Acked-by: Jason Baron <jbaron@redhat.com>
Thanks,
-Jason
^ permalink raw reply [flat|nested] 8+ messages in thread* Re: [PATCH] jump_label_inc may return before the code is patched
2011-10-18 20:54 ` Jason Baron
@ 2011-10-19 7:03 ` Gleb Natapov
0 siblings, 0 replies; 8+ messages in thread
From: Gleb Natapov @ 2011-10-19 7:03 UTC (permalink / raw)
To: Jason Baron; +Cc: linux-kernel, Peter Zijlstra, Steven Rostedt
On Tue, Oct 18, 2011 at 04:54:41PM -0400, Jason Baron wrote:
> On Tue, Oct 18, 2011 at 07:55:51PM +0200, Gleb Natapov wrote:
> > If cpu A calls jump_label_inc() just after atomic_add_return() is
> > called by cpu B, atomic_inc_not_zero() will return value greater then
> > zero and jump_label_inc() will return to a caller before jump_label_update()
> > finishes its job on cpu B.
> >
> > Signed-off-by: Gleb Natapov <gleb@redhat.com>
> > diff --git a/kernel/jump_label.c b/kernel/jump_label.c
> > index a8ce450..e6f1f24 100644
> > --- a/kernel/jump_label.c
> > +++ b/kernel/jump_label.c
> > @@ -66,8 +66,9 @@ void jump_label_inc(struct jump_label_key *key)
> > return;
> >
> > jump_label_lock();
> > - if (atomic_add_return(1, &key->enabled) == 1)
> > + if (atomic_read(&key->enabled) == 0)
> > jump_label_update(key, JUMP_LABEL_ENABLE);
> > + atomic_inc(&key->enabled);
> > jump_label_unlock();
> > }
> >
>
> agreed, we shouldn't return before the update happens...did this cause any
> actual problem in practice? Or just observed from code inspection?
>
It did. I am debugging strange oopses in perf code that happen when I
create and destroy hw events on multiple cpus in parallel. At some point
I started to suspect that jump labels are not working properly and
printks confirmed that sometimes static_branch() is not taken when
->enabled is not zero. I compiled kernel without jump label support and,
as far as my testing goes, oopses disappeared. Then I found the bug by
looking at the code. Strangely enough this patch alone didn't fix oopses
yet, so some other problems are probably lurking somewhere. I am going
on vocation till next week. Will debug furtherer upon return.
> Acked-by: Jason Baron <jbaron@redhat.com>
>
> Thanks,
>
> -Jason
--
Gleb.
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [PATCH] jump_label_inc may return before the code is patched
2011-10-18 17:55 [PATCH] jump_label_inc may return before the code is patched Gleb Natapov
2011-10-18 20:54 ` Jason Baron
@ 2011-10-18 21:06 ` Steven Rostedt
2011-11-02 15:21 ` Gleb Natapov
2011-11-18 23:12 ` [tip:perf/core] jump_label: " tip-bot for Gleb Natapov
2011-12-06 6:27 ` tip-bot for Gleb Natapov
3 siblings, 1 reply; 8+ messages in thread
From: Steven Rostedt @ 2011-10-18 21:06 UTC (permalink / raw)
To: Gleb Natapov; +Cc: linux-kernel, Jason Baron, Peter Zijlstra
On Tue, 2011-10-18 at 19:55 +0200, Gleb Natapov wrote:
> If cpu A calls jump_label_inc() just after atomic_add_return() is
> called by cpu B, atomic_inc_not_zero() will return value greater then
> zero and jump_label_inc() will return to a caller before jump_label_update()
> finishes its job on cpu B.
OK, I see what you are saying. There's a race here that jump_label_inc
may return before jump labels are actually activated. I have no issue
with this change. This guarantees that jump labels will be active on
return of jump_label_inc().
I'm assuming that jump_label_update() does memory barries, as it does
modify code, and would be itself a synchronization point.
Acked-by: Steven Rostedt <rostedt@goodmis.org>
-- Steve
>
> Signed-off-by: Gleb Natapov <gleb@redhat.com>
> diff --git a/kernel/jump_label.c b/kernel/jump_label.c
> index a8ce450..e6f1f24 100644
> --- a/kernel/jump_label.c
> +++ b/kernel/jump_label.c
> @@ -66,8 +66,9 @@ void jump_label_inc(struct jump_label_key *key)
> return;
>
> jump_label_lock();
> - if (atomic_add_return(1, &key->enabled) == 1)
> + if (atomic_read(&key->enabled) == 0)
> jump_label_update(key, JUMP_LABEL_ENABLE);
> + atomic_inc(&key->enabled);
> jump_label_unlock();
> }
>
> --
> Gleb.
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [PATCH] jump_label_inc may return before the code is patched
2011-10-18 21:06 ` Steven Rostedt
@ 2011-11-02 15:21 ` Gleb Natapov
2011-11-02 15:42 ` Steven Rostedt
0 siblings, 1 reply; 8+ messages in thread
From: Gleb Natapov @ 2011-11-02 15:21 UTC (permalink / raw)
To: Steven Rostedt; +Cc: linux-kernel, Jason Baron, Peter Zijlstra, mingo
On Tue, Oct 18, 2011 at 05:06:25PM -0400, Steven Rostedt wrote:
> On Tue, 2011-10-18 at 19:55 +0200, Gleb Natapov wrote:
> > If cpu A calls jump_label_inc() just after atomic_add_return() is
> > called by cpu B, atomic_inc_not_zero() will return value greater then
> > zero and jump_label_inc() will return to a caller before jump_label_update()
> > finishes its job on cpu B.
>
> OK, I see what you are saying. There's a race here that jump_label_inc
> may return before jump labels are actually activated. I have no issue
> with this change. This guarantees that jump labels will be active on
> return of jump_label_inc().
>
> I'm assuming that jump_label_update() does memory barries, as it does
> modify code, and would be itself a synchronization point.
>
> Acked-by: Steven Rostedt <rostedt@goodmis.org>
>
So through what tree this should go to Linus' git?
> -- Steve
>
> >
> > Signed-off-by: Gleb Natapov <gleb@redhat.com>
> > diff --git a/kernel/jump_label.c b/kernel/jump_label.c
> > index a8ce450..e6f1f24 100644
> > --- a/kernel/jump_label.c
> > +++ b/kernel/jump_label.c
> > @@ -66,8 +66,9 @@ void jump_label_inc(struct jump_label_key *key)
> > return;
> >
> > jump_label_lock();
> > - if (atomic_add_return(1, &key->enabled) == 1)
> > + if (atomic_read(&key->enabled) == 0)
> > jump_label_update(key, JUMP_LABEL_ENABLE);
> > + atomic_inc(&key->enabled);
> > jump_label_unlock();
> > }
> >
> > --
> > Gleb.
>
--
Gleb.
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [PATCH] jump_label_inc may return before the code is patched
2011-11-02 15:21 ` Gleb Natapov
@ 2011-11-02 15:42 ` Steven Rostedt
0 siblings, 0 replies; 8+ messages in thread
From: Steven Rostedt @ 2011-11-02 15:42 UTC (permalink / raw)
To: Gleb Natapov; +Cc: linux-kernel, Jason Baron, Peter Zijlstra, mingo
On Wed, 2011-11-02 at 17:21 +0200, Gleb Natapov wrote:
> On Tue, Oct 18, 2011 at 05:06:25PM -0400, Steven Rostedt wrote:
> > On Tue, 2011-10-18 at 19:55 +0200, Gleb Natapov wrote:
> > > If cpu A calls jump_label_inc() just after atomic_add_return() is
> > > called by cpu B, atomic_inc_not_zero() will return value greater then
> > > zero and jump_label_inc() will return to a caller before jump_label_update()
> > > finishes its job on cpu B.
> >
> > OK, I see what you are saying. There's a race here that jump_label_inc
> > may return before jump labels are actually activated. I have no issue
> > with this change. This guarantees that jump labels will be active on
> > return of jump_label_inc().
> >
> > I'm assuming that jump_label_update() does memory barries, as it does
> > modify code, and would be itself a synchronization point.
> >
> > Acked-by: Steven Rostedt <rostedt@goodmis.org>
> >
> So through what tree this should go to Linus' git?
I'll pull it in. I'm currently scrambling around getting back up to
speed after a 11 day conference spree.
-- Steve
^ permalink raw reply [flat|nested] 8+ messages in thread
* [tip:perf/core] jump_label: jump_label_inc may return before the code is patched
2011-10-18 17:55 [PATCH] jump_label_inc may return before the code is patched Gleb Natapov
2011-10-18 20:54 ` Jason Baron
2011-10-18 21:06 ` Steven Rostedt
@ 2011-11-18 23:12 ` tip-bot for Gleb Natapov
2011-12-06 6:27 ` tip-bot for Gleb Natapov
3 siblings, 0 replies; 8+ messages in thread
From: tip-bot for Gleb Natapov @ 2011-11-18 23:12 UTC (permalink / raw)
To: linux-tip-commits
Cc: linux-kernel, hpa, mingo, a.p.zijlstra, gleb, rostedt, tglx,
jbaron
Commit-ID: c8452afb7426f7e21388492f40227582e3e83879
Gitweb: http://git.kernel.org/tip/c8452afb7426f7e21388492f40227582e3e83879
Author: Gleb Natapov <gleb@redhat.com>
AuthorDate: Tue, 18 Oct 2011 19:55:51 +0200
Committer: Steven Rostedt <rostedt@goodmis.org>
CommitDate: Mon, 7 Nov 2011 11:02:34 -0500
jump_label: jump_label_inc may return before the code is patched
If cpu A calls jump_label_inc() just after atomic_add_return() is
called by cpu B, atomic_inc_not_zero() will return value greater then
zero and jump_label_inc() will return to a caller before jump_label_update()
finishes its job on cpu B.
Link: http://lkml.kernel.org/r/20111018175551.GH17571@redhat.com
Cc: stable@vger.kernel.org
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Jason Baron <jbaron@redhat.com>
Signed-off-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
kernel/jump_label.c | 3 ++-
1 files changed, 2 insertions(+), 1 deletions(-)
diff --git a/kernel/jump_label.c b/kernel/jump_label.c
index a8ce450..e6f1f24 100644
--- a/kernel/jump_label.c
+++ b/kernel/jump_label.c
@@ -66,8 +66,9 @@ void jump_label_inc(struct jump_label_key *key)
return;
jump_label_lock();
- if (atomic_add_return(1, &key->enabled) == 1)
+ if (atomic_read(&key->enabled) == 0)
jump_label_update(key, JUMP_LABEL_ENABLE);
+ atomic_inc(&key->enabled);
jump_label_unlock();
}
^ permalink raw reply related [flat|nested] 8+ messages in thread
* [tip:perf/core] jump_label: jump_label_inc may return before the code is patched
2011-10-18 17:55 [PATCH] jump_label_inc may return before the code is patched Gleb Natapov
` (2 preceding siblings ...)
2011-11-18 23:12 ` [tip:perf/core] jump_label: " tip-bot for Gleb Natapov
@ 2011-12-06 6:27 ` tip-bot for Gleb Natapov
3 siblings, 0 replies; 8+ messages in thread
From: tip-bot for Gleb Natapov @ 2011-12-06 6:27 UTC (permalink / raw)
To: linux-tip-commits
Cc: linux-kernel, hpa, mingo, a.p.zijlstra, gleb, rostedt, tglx,
jbaron
Commit-ID: bbbf7af4bf8fc69bc751818cf30521080fa47dcb
Gitweb: http://git.kernel.org/tip/bbbf7af4bf8fc69bc751818cf30521080fa47dcb
Author: Gleb Natapov <gleb@redhat.com>
AuthorDate: Tue, 18 Oct 2011 19:55:51 +0200
Committer: Steven Rostedt <rostedt@goodmis.org>
CommitDate: Mon, 5 Dec 2011 13:28:46 -0500
jump_label: jump_label_inc may return before the code is patched
If cpu A calls jump_label_inc() just after atomic_add_return() is
called by cpu B, atomic_inc_not_zero() will return value greater then
zero and jump_label_inc() will return to a caller before jump_label_update()
finishes its job on cpu B.
Link: http://lkml.kernel.org/r/20111018175551.GH17571@redhat.com
Cc: stable@vger.kernel.org
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Jason Baron <jbaron@redhat.com>
Signed-off-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
kernel/jump_label.c | 3 ++-
1 files changed, 2 insertions(+), 1 deletions(-)
diff --git a/kernel/jump_label.c b/kernel/jump_label.c
index bbdfe2a..66ff710 100644
--- a/kernel/jump_label.c
+++ b/kernel/jump_label.c
@@ -66,8 +66,9 @@ void jump_label_inc(struct jump_label_key *key)
return;
jump_label_lock();
- if (atomic_add_return(1, &key->enabled) == 1)
+ if (atomic_read(&key->enabled) == 0)
jump_label_update(key, JUMP_LABEL_ENABLE);
+ atomic_inc(&key->enabled);
jump_label_unlock();
}
^ permalink raw reply related [flat|nested] 8+ messages in thread