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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>
This commit is contained in:
Paul E. McKenney 2010-02-22 17:05:03 -08:00 committed by Ingo Molnar
parent 1304afb225
commit 3acd9eb31c
2 changed files with 2 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
kernel/rcutree.c
View File

@ -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++)

3
kernel/rcutree_plugin.h
View File

@ -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);
}
}