| Message ID | bd911cd9-1fe9-447c-85e0-ea811a1dc896@paulmck-laptop (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [v2] 2/5] rcu: Remove READ_ONCE() for rdp->gpwrap access in __note_gp_changes() | expand |
On Thu, Feb 06, 2025 at 02:15:09AM -0800, Paul E. McKenney wrote: > The WARN_ON_ONCE() in ct_kernel_exit_state() follows the call to > ct_state_inc(), which means that RCU is not watching this WARN_ON_ONCE(). > This can (and does) result in extraneous lockdep warnings when this > WARN_ON_ONCE() triggers. These extraneous warnings are the opposite > of helpful. > > Therefore, invert the WARN_ON_ONCE() condition and move it before the > call to ct_state_inc(). This does mean that the ct_state_inc() return > value can no longer be used in the WARN_ON_ONCE() condition, so discard > this return value and instead use a call to rcu_is_watching_curr_cpu(). > This call is executed only in CONFIG_RCU_EQS_DEBUG=y kernels, so there > is no added overhead in production use. > > Reported-by: Breno Leitao <leitao@debian.org> > Signed-off-by: Paul E. McKenney <paulmck@kernel.org> > Reviewed-by: Valentin Schneider <vschneid@redhat.com> > Reviewed-by: Frederic Weisbecker <frederic@kernel.org> > Queued at: git://git.kernel.org/pub/scm/linux/kernel/git/rcu/linux.git misc.2025.02.06a I added the "context_tracking:" tag to the title while I'm at it. Regards, Boqun > diff --git a/kernel/context_tracking.c b/kernel/context_tracking.c > index 938c48952d26..fb5be6e9b423 100644 > --- a/kernel/context_tracking.c > +++ b/kernel/context_tracking.c > @@ -80,17 +80,16 @@ static __always_inline void rcu_task_trace_heavyweight_exit(void) > */ > static noinstr void ct_kernel_exit_state(int offset) > { > - int seq; > - > /* > * CPUs seeing atomic_add_return() must see prior RCU read-side > * critical sections, and we also must force ordering with the > * next idle sojourn. > */ > rcu_task_trace_heavyweight_enter(); // Before CT state update! > - seq = ct_state_inc(offset); > - // RCU is no longer watching. Better be in extended quiescent state! > - WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && (seq & CT_RCU_WATCHING)); > + // RCU is still watching. Better not be in extended quiescent state! > + WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !rcu_is_watching_curr_cpu()); > + (void)ct_state_inc(offset); > + // RCU is no longer watching. > } > > /* >
diff --git a/kernel/context_tracking.c b/kernel/context_tracking.c index 938c48952d26..fb5be6e9b423 100644 --- a/kernel/context_tracking.c +++ b/kernel/context_tracking.c @@ -80,17 +80,16 @@ static __always_inline void rcu_task_trace_heavyweight_exit(void) */ static noinstr void ct_kernel_exit_state(int offset) { - int seq; - /* * CPUs seeing atomic_add_return() must see prior RCU read-side * critical sections, and we also must force ordering with the * next idle sojourn. */ rcu_task_trace_heavyweight_enter(); // Before CT state update! - seq = ct_state_inc(offset); - // RCU is no longer watching. Better be in extended quiescent state! - WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && (seq & CT_RCU_WATCHING)); + // RCU is still watching. Better not be in extended quiescent state! + WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !rcu_is_watching_curr_cpu()); + (void)ct_state_inc(offset); + // RCU is no longer watching. } /*