From b0e165c035b13e1074fa0b555318bd9cb7102558 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Date: Sun, 13 Sep 2009 09:15:09 -0700 Subject: rcu: Add debug checks to TREE_PREEMPT_RCU for premature grace periods Check to make sure that there are no blocked tasks for the previous grace period while initializing for the next grace period, verify that rcu_preempt_qs() is given the correct CPU number and is never called for an offline CPU. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: akpm@linux-foundation.org Cc: mathieu.desnoyers@polymtl.ca Cc: josh@joshtriplett.org Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu LKML-Reference: <12528585111986-git-send-email-> Signed-off-by: Ingo Molnar <mingo@elte.hu> --- kernel/rcutree_plugin.h | 25 +++++++++++++++++++++++++ 1 file changed, 25 insertions(+) (limited to 'kernel/rcutree_plugin.h') diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index 47789369ea59..b8e4b0384f00 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -86,6 +86,7 @@ static void rcu_preempt_qs(int cpu) if (t->rcu_read_lock_nesting && (t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) { + WARN_ON_ONCE(cpu != smp_processor_id()); /* Possibly blocking in an RCU read-side critical section. */ rdp = rcu_preempt_state.rda[cpu]; @@ -103,7 +104,11 @@ static void rcu_preempt_qs(int cpu) * state for the current grace period), then as long * as that task remains queued, the current grace period * cannot end. + * + * But first, note that the current CPU must still be + * on line! */ + WARN_ON_ONCE((rdp->grpmask & rnp->qsmaskinit) == 0); phase = !(rnp->qsmask & rdp->grpmask) ^ (rnp->gpnum & 0x1); list_add(&t->rcu_node_entry, &rnp->blocked_tasks[phase]); smp_mb(); /* Ensure later ctxt swtch seen after above. */ @@ -258,6 +263,18 @@ static void rcu_print_task_stall(struct rcu_node *rnp) #endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */ +/* + * Check that the list of blocked tasks for the newly completed grace + * period is in fact empty. It is a serious bug to complete a grace + * period that still has RCU readers blocked! This function must be + * invoked -before- updating this rnp's ->gpnum, and the rnp's ->lock + * must be held by the caller. + */ +static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp) +{ + WARN_ON_ONCE(!list_empty(&rnp->blocked_tasks[rnp->gpnum & 0x1])); +} + /* * Check for preempted RCU readers for the specified rcu_node structure. * If the caller needs a reliable answer, it must hold the rcu_node's @@ -450,6 +467,14 @@ static void rcu_print_task_stall(struct rcu_node *rnp) #endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */ +/* + * Because there is no preemptable RCU, there can be no readers blocked, + * so there is no need to check for blocked tasks. + */ +static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp) +{ +} + /* * Because preemptable RCU does not exist, there are never any preempted * RCU readers. -- cgit v1.2.3-58-ga151