rcu: fix lockdep splat in wake_affine()
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From: Peter Zijlstra on 16 Jun 2010 02:30 On Tue, 2010-06-15 at 15:29 -0700, Paul E. McKenney wrote: > From: Daniel J Blueman <daniel.blueman(a)gmail.com> > > With 2.6.35-rc1 and your patch in the context below, we still see > "include/linux/cgroup.h:534 invoked rcu_dereference_check() without > protection!", so need this additional patch: > > Acquire read-side RCU lock around task_group() calls, addressing > "include/linux/cgroup.h:534 invoked rcu_dereference_check() without > protection!" warning. Uhm,. this is all just slapping in rcu_read_lock() to make the warning go away, without explanation of what and why. Its not obvious what the races is, nor how its handled. > Signed-off-by: Daniel J Blueman <daniel.blueman(a)gmail.com> > Signed-off-by: Paul E. McKenney <paulmck(a)linux.vnet.ibm.com> > --- > kernel/sched_fair.c | 2 ++ > 1 files changed, 2 insertions(+), 0 deletions(-) > > diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c > index eed35ed..ca56133 100644 > --- a/kernel/sched_fair.c > +++ b/kernel/sched_fair.c > @@ -1240,6 +1240,7 @@ static int wake_affine(struct sched_domain *sd, struct task_struct *p, int sync) > * effect of the currently running task from the load > * of the current CPU: > */ > + rcu_read_lock(); > if (sync) { > tg = task_group(current); > weight = current->se.load.weight; > @@ -1249,6 +1250,7 @@ static int wake_affine(struct sched_domain *sd, struct task_struct *p, int sync) > } > > tg = task_group(p); > + rcu_read_unlock(); > weight = p->se.load.weight; > > /* -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Paul E. McKenney on 16 Jun 2010 19:10
On Wed, Jun 16, 2010 at 08:23:11AM +0200, Peter Zijlstra wrote: > On Tue, 2010-06-15 at 15:29 -0700, Paul E. McKenney wrote: > > From: Daniel J Blueman <daniel.blueman(a)gmail.com> > > > > With 2.6.35-rc1 and your patch in the context below, we still see > > "include/linux/cgroup.h:534 invoked rcu_dereference_check() without > > protection!", so need this additional patch: > > > > Acquire read-side RCU lock around task_group() calls, addressing > > "include/linux/cgroup.h:534 invoked rcu_dereference_check() without > > protection!" warning. > > Uhm,. this is all just slapping in rcu_read_lock() to make the warning > go away, without explanation of what and why. > > Its not obvious what the races is, nor how its handled. Please let me know if my explanation in a recent email covers this. If so, I will add it to the commit log. If not, well, back to the drawing board, I guess. ;-) Thanx, Paul > > Signed-off-by: Daniel J Blueman <daniel.blueman(a)gmail.com> > > Signed-off-by: Paul E. McKenney <paulmck(a)linux.vnet.ibm.com> > > --- > > kernel/sched_fair.c | 2 ++ > > 1 files changed, 2 insertions(+), 0 deletions(-) > > > > diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c > > index eed35ed..ca56133 100644 > > --- a/kernel/sched_fair.c > > +++ b/kernel/sched_fair.c > > @@ -1240,6 +1240,7 @@ static int wake_affine(struct sched_domain *sd, struct task_struct *p, int sync) > > * effect of the currently running task from the load > > * of the current CPU: > > */ > > + rcu_read_lock(); > > if (sync) { > > tg = task_group(current); > > weight = current->se.load.weight; > > @@ -1249,6 +1250,7 @@ static int wake_affine(struct sched_domain *sd, struct task_struct *p, int sync) > > } > > > > tg = task_group(p); > > + rcu_read_unlock(); > > weight = p->se.load.weight; > > > > /* > > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |