| Message ID | 1328125319-5205-4-git-send-email-paulmck@linux.vnet.ibm.com |
|---|---|
| State | Superseded |
| Headers | show |
On Wed, Feb 01, 2012 at 11:41:22AM -0800, Paul E. McKenney wrote: > The push for energy efficiency will require that RCU tag rcu_head > structures to indicate whether or not their invocation is time critical. > This tagging is best carried out in the bottom bits of the ->next > pointers in the rcu_head structures. This tagging requires that the > rcu_head structures be properly aligned, so this commit adds the required > diagnostics. > --- a/kernel/rcutree.c > +++ b/kernel/rcutree.c > @@ -1707,6 +1707,7 @@ __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu), > unsigned long flags; > struct rcu_data *rdp; > > + WARN_ON_ONCE((unsigned long)head & 0x3); /* Misaligned rcu_head! */ I wonder if this should go out in one of the wrapper macros, so that the _ONCE means once per call site? - Josh Triplett
On Wed, Feb 01, 2012 at 11:41:22AM -0800, Paul E. McKenney wrote: > From: "Paul E. McKenney" <paul.mckenney@linaro.org> > > The push for energy efficiency will require that RCU tag rcu_head > structures to indicate whether or not their invocation is time critical. > This tagging is best carried out in the bottom bits of the ->next > pointers in the rcu_head structures. This tagging requires that the > rcu_head structures be properly aligned, so this commit adds the required > diagnostics. > > Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org> > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> > --- > kernel/rcutree.c | 1 + > 1 files changed, 1 insertions(+), 0 deletions(-) > > diff --git a/kernel/rcutree.c b/kernel/rcutree.c > index d0f8e64..4655f3e 100644 > --- a/kernel/rcutree.c > +++ b/kernel/rcutree.c > @@ -1707,6 +1707,7 @@ __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu), > unsigned long flags; > struct rcu_data *rdp; > > + WARN_ON_ONCE((unsigned long)head & 0x3); /* Misaligned rcu_head! */ > debug_rcu_head_queue(head); Upon further checking: static inline void debug_rcu_head_queue(struct rcu_head *head) { WARN_ON_ONCE((unsigned long)head & 0x3); :) - Josh Triplett
On Wed, Feb 01, 2012 at 05:00:26PM -0800, Josh Triplett wrote: > On Wed, Feb 01, 2012 at 11:41:22AM -0800, Paul E. McKenney wrote: > > The push for energy efficiency will require that RCU tag rcu_head > > structures to indicate whether or not their invocation is time critical. > > This tagging is best carried out in the bottom bits of the ->next > > pointers in the rcu_head structures. This tagging requires that the > > rcu_head structures be properly aligned, so this commit adds the required > > diagnostics. > > > --- a/kernel/rcutree.c > > +++ b/kernel/rcutree.c > > @@ -1707,6 +1707,7 @@ __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu), > > unsigned long flags; > > struct rcu_data *rdp; > > > > + WARN_ON_ONCE((unsigned long)head & 0x3); /* Misaligned rcu_head! */ > > I wonder if this should go out in one of the wrapper macros, so that the > _ONCE means once per call site? Certainly past experience introducing lockdep-RCU would argue that way. ;-) However, my testing thus far (famous last words!) has found no misalignments. So I expect that these will be caught as they are inserted, so one at a time should be fine. Thanx, Paul
On Wed, Feb 01, 2012 at 05:01:46PM -0800, Josh Triplett wrote: > On Wed, Feb 01, 2012 at 11:41:22AM -0800, Paul E. McKenney wrote: > > From: "Paul E. McKenney" <paul.mckenney@linaro.org> > > > > The push for energy efficiency will require that RCU tag rcu_head > > structures to indicate whether or not their invocation is time critical. > > This tagging is best carried out in the bottom bits of the ->next > > pointers in the rcu_head structures. This tagging requires that the > > rcu_head structures be properly aligned, so this commit adds the required > > diagnostics. > > > > Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org> > > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> > > --- > > kernel/rcutree.c | 1 + > > 1 files changed, 1 insertions(+), 0 deletions(-) > > > > diff --git a/kernel/rcutree.c b/kernel/rcutree.c > > index d0f8e64..4655f3e 100644 > > --- a/kernel/rcutree.c > > +++ b/kernel/rcutree.c > > @@ -1707,6 +1707,7 @@ __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu), > > unsigned long flags; > > struct rcu_data *rdp; > > > > + WARN_ON_ONCE((unsigned long)head & 0x3); /* Misaligned rcu_head! */ > > debug_rcu_head_queue(head); > > Upon further checking: > > static inline void debug_rcu_head_queue(struct rcu_head *head) > { > WARN_ON_ONCE((unsigned long)head & 0x3); > > :) Fair point! I guess that we really only need one of these. ;-) I have kept the unconditional one and removed the one hidden under CONFIG_DEBUG_OBJECTS_RCU_HEAD, but in a separate commit with your Reported-by. Thanx, Paul
On Thu, Feb 02, 2012 at 08:22:35AM -0800, Paul E. McKenney wrote: > On Wed, Feb 01, 2012 at 05:00:26PM -0800, Josh Triplett wrote: > > On Wed, Feb 01, 2012 at 11:41:22AM -0800, Paul E. McKenney wrote: > > > The push for energy efficiency will require that RCU tag rcu_head > > > structures to indicate whether or not their invocation is time critical. > > > This tagging is best carried out in the bottom bits of the ->next > > > pointers in the rcu_head structures. This tagging requires that the > > > rcu_head structures be properly aligned, so this commit adds the required > > > diagnostics. > > > > > --- a/kernel/rcutree.c > > > +++ b/kernel/rcutree.c > > > @@ -1707,6 +1707,7 @@ __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu), > > > unsigned long flags; > > > struct rcu_data *rdp; > > > > > > + WARN_ON_ONCE((unsigned long)head & 0x3); /* Misaligned rcu_head! */ > > > > I wonder if this should go out in one of the wrapper macros, so that the > > _ONCE means once per call site? > > Certainly past experience introducing lockdep-RCU would argue that way. ;-) > > However, my testing thus far (famous last words!) has found no > misalignments. So I expect that these will be caught as they are > inserted, so one at a time should be fine. Fair enough. Doesn't seem worth introducing a new wrapper macro for, then, since it doesn't look like an appropriate one currently exists. - Josh Triplett
diff --git a/kernel/rcutree.c b/kernel/rcutree.c index d0f8e64..4655f3e 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -1707,6 +1707,7 @@ __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu), unsigned long flags; struct rcu_data *rdp; + WARN_ON_ONCE((unsigned long)head & 0x3); /* Misaligned rcu_head! */ debug_rcu_head_queue(head); head->func = func; head->next = NULL;