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authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2010-02-22 17:05:03 -0800
committerIngo Molnar <mingo@elte.hu>2010-02-25 10:34:59 +0100
commit3acd9eb31c5f7eb97cb2009fa41472710fb4a10f (patch)
treea339775ed9683bdf0f4d7b47a75648a6f86a8446
parent1304afb225288a2e250d6a7495462c28e5509cbb (diff)
rcu: Fix deadlock in TREE_PREEMPT_RCU CPU stall detection
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> Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com 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 Cc: dhowells@redhat.com LKML-Reference: <1266887105-1528-19-git-send-email-paulmck@linux.vnet.ibm.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
-rw-r--r--kernel/rcutree.c2
-rw-r--r--kernel/rcutree_plugin.h3
2 files changed, 2 insertions, 3 deletions
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 65a807b4f58..b07be37d2aa 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 a8b2e834fd3..aecfe37e011 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);
}
}