* [PATCH RFC 1/2] rcu: fix deadlock in TREE_PREEMPT_RCU CPU stall detection
2010-02-23 1:46 [PATCH RFC] rcu: RCU CPU stall patches backported to 2.6.33-rc8 Paul E. McKenney
@ 2010-02-23 1:47 ` Paul E. McKenney
2010-02-23 1:47 ` [PATCH RFC 2/2] rcu: add RCU_CPU_STALL_VERBOSE to dump detailed per-task information Paul E. McKenney
1 sibling, 0 replies; 3+ messages in thread
From: Paul E. McKenney @ 2010-02-23 1:47 UTC (permalink / raw)
To: linux-kernel; +Cc: tglx, jkacur, Paul E. McKenney
Under TREE_PREEMPT_RCU, print_other_cpu_stall() invokes
rcu_print_task_stall() with the root rcu_node structure's ->lock held,
and rcu_print_task_stall() acquires that same lock for self-deadlock.
Fix this by removing the lock acquisition from rcu_print_task_stall(),
and making all callers acquire the lock instead.
Tested-by: John Kacur <jkacur@redhat.com>
Tested-by: Thomas Gleixner <tglx@linutronix.de>
Located-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
kernel/rcutree.c | 2 ++
kernel/rcutree_plugin.h | 3 ---
2 files changed, 2 insertions(+), 3 deletions(-)
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 53ae959..6f652f1 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -458,7 +458,9 @@ static void print_other_cpu_stall(struct rcu_state *rsp)
printk(KERN_ERR "INFO: RCU detected CPU stalls:");
rcu_for_each_leaf_node(rsp, rnp) {
+ raw_spin_lock_irqsave(&rnp->lock, flags);
rcu_print_task_stall(rnp);
+ raw_spin_unlock_irqrestore(&rnp->lock, flags);
if (rnp->qsmask == 0)
continue;
for (cpu = 0; cpu <= rnp->grphi - rnp->grplo; cpu++)
diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index 37fbccd..e31cda7 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -306,18 +306,15 @@ EXPORT_SYMBOL_GPL(__rcu_read_unlock);
*/
static void rcu_print_task_stall(struct rcu_node *rnp)
{
- unsigned long flags;
struct list_head *lp;
int phase;
struct task_struct *t;
if (rcu_preempted_readers(rnp)) {
- spin_lock_irqsave(&rnp->lock, flags);
phase = rnp->gpnum & 0x1;
lp = &rnp->blocked_tasks[phase];
list_for_each_entry(t, lp, rcu_node_entry)
printk(" P%d", t->pid);
- spin_unlock_irqrestore(&rnp->lock, flags);
}
}
--
1.6.6
^ permalink raw reply related [flat|nested] 3+ messages in thread* [PATCH RFC 2/2] rcu: add RCU_CPU_STALL_VERBOSE to dump detailed per-task information
2010-02-23 1:46 [PATCH RFC] rcu: RCU CPU stall patches backported to 2.6.33-rc8 Paul E. McKenney
2010-02-23 1:47 ` [PATCH RFC 1/2] rcu: fix deadlock in TREE_PREEMPT_RCU CPU stall detection Paul E. McKenney
@ 2010-02-23 1:47 ` Paul E. McKenney
1 sibling, 0 replies; 3+ messages in thread
From: Paul E. McKenney @ 2010-02-23 1:47 UTC (permalink / raw)
To: linux-kernel; +Cc: tglx, jkacur, Paul E. McKenney
When RCU detects a grace-period stall, it currently just prints out the
PID of any tasks doing the stalling. This patch adds RCU_CPU_STALL_VERBOSE,
which enables the more-verbose reporting from sched_show_task().
Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
kernel/rcutree.c | 4 +++
kernel/rcutree.h | 1 +
kernel/rcutree_plugin.h | 52 +++++++++++++++++++++++++++++++++++++++++++++++
lib/Kconfig.debug | 12 ++++++++++
4 files changed, 69 insertions(+), 0 deletions(-)
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 6f652f1..ce642e2 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -471,6 +471,10 @@ static void print_other_cpu_stall(struct rcu_state *rsp)
smp_processor_id(), (long)(jiffies - rsp->gp_start));
trigger_all_cpu_backtrace();
+ /* If so configured, complain about tasks blocking the grace period. */
+
+ rcu_print_detail_task_stall(rsp);
+
force_quiescent_state(rsp, 0); /* Kick them all. */
}
diff --git a/kernel/rcutree.h b/kernel/rcutree.h
index d2a0046..458c047 100644
--- a/kernel/rcutree.h
+++ b/kernel/rcutree.h
@@ -347,6 +347,7 @@ static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp,
unsigned long flags);
#endif /* #ifdef CONFIG_HOTPLUG_CPU */
#ifdef CONFIG_RCU_CPU_STALL_DETECTOR
+static void rcu_print_detail_task_stall(struct rcu_state *rsp);
static void rcu_print_task_stall(struct rcu_node *rnp);
#endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp);
diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index e31cda7..7021fde 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -300,6 +300,50 @@ EXPORT_SYMBOL_GPL(__rcu_read_unlock);
#ifdef CONFIG_RCU_CPU_STALL_DETECTOR
+#ifdef CONFIG_RCU_CPU_STALL_VERBOSE
+
+/*
+ * Dump detailed information for all tasks blocking the current RCU
+ * grace period on the specified rcu_node structure.
+ */
+static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp)
+{
+ unsigned long flags;
+ struct list_head *lp;
+ int phase;
+ struct task_struct *t;
+
+ if (rcu_preempted_readers(rnp)) {
+ raw_spin_lock_irqsave(&rnp->lock, flags);
+ phase = rnp->gpnum & 0x1;
+ lp = &rnp->blocked_tasks[phase];
+ list_for_each_entry(t, lp, rcu_node_entry)
+ sched_show_task(t);
+ raw_spin_unlock_irqrestore(&rnp->lock, flags);
+ }
+}
+
+/*
+ * Dump detailed information for all tasks blocking the current RCU
+ * grace period.
+ */
+static void rcu_print_detail_task_stall(struct rcu_state *rsp)
+{
+ struct rcu_node *rnp = rcu_get_root(rsp);
+
+ rcu_print_detail_task_stall_rnp(rnp);
+ rcu_for_each_leaf_node(rsp, rnp)
+ rcu_print_detail_task_stall_rnp(rnp);
+}
+
+#else /* #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */
+
+static void rcu_print_detail_task_stall(struct rcu_state *rsp)
+{
+}
+
+#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */
+
/*
* Scan the current list of tasks blocked within RCU read-side critical
* sections, printing out the tid of each.
@@ -742,6 +786,14 @@ static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags)
* Because preemptable RCU does not exist, we never have to check for
* tasks blocked within RCU read-side critical sections.
*/
+static void rcu_print_detail_task_stall(struct rcu_state *rsp)
+{
+}
+
+/*
+ * Because preemptable RCU does not exist, we never have to check for
+ * tasks blocked within RCU read-side critical sections.
+ */
static void rcu_print_task_stall(struct rcu_node *rnp)
{
}
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 25c3ed5..7500988 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -769,6 +769,18 @@ config RCU_CPU_STALL_DETECTOR
Say N if you are unsure.
+config RCU_CPU_STALL_VERBOSE
+ bool "Print additional per-task information for RCU_CPU_STALL_DETECTOR"
+ depends on RCU_CPU_STALL_DETECTOR && TREE_PREEMPT_RCU
+ default n
+ help
+ This option causes RCU to printk detailed per-task information
+ for any tasks that are stalling the current RCU grace period.
+
+ Say N if you are unsure.
+
+ Say Y if you want to enable such checks.
+
config KPROBES_SANITY_TEST
bool "Kprobes sanity tests"
depends on DEBUG_KERNEL
--
1.6.6
^ permalink raw reply related [flat|nested] 3+ messages in thread