Prev: [PATCH tip/core/rcu 08/21] vfs: apply lockdep-based checking to rcu_dereference() uses
Next: [PATCH tip/core/rcu 02/21] rcu: add lockdep-enabled variants of rcu_dereference()
From: Paul E. McKenney on 22 Feb 2010 20:10
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(a)redhat.com>
Tested-by: Thomas Gleixner <tglx(a)linutronix.de>
Located-by: Thomas Gleixner <tglx(a)linutronix.de>
Signed-off-by: Paul E. McKenney <paulmck(a)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 65a807b..b07be37 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -476,7 +476,9 @@ 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 a8b2e83..aecfe37 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -318,18 +318,15 @@ 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)) {
- 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)
printk(" P%d", t->pid);
- raw_spin_unlock_irqrestore(&rnp->lock, flags);
}
}

--
1.6.6

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Prev: [PATCH tip/core/rcu 08/21] vfs: apply lockdep-based checking to rcu_dereference() uses
Next: [PATCH tip/core/rcu 02/21] rcu: add lockdep-enabled variants of rcu_dereference()