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authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2014-10-22 10:00:05 -0700
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2014-10-23 07:51:17 -0700
commitb2c4623dcd07af4b8ae3b56ae5f879e281c7b4f8 (patch)
tree8a0aaf80f950011fafb6743d42457a22412ae6dd /kernel/cpu.c
parentf114040e3ea6e07372334ade75d1ee0775c355e1 (diff)
rcu: More on deadlock between CPU hotplug and expedited grace periods
Commit dd56af42bd82 (rcu: Eliminate deadlock between CPU hotplug and expedited grace periods) was incomplete. Although it did eliminate deadlocks involving synchronize_sched_expedited()'s acquisition of cpu_hotplug.lock via get_online_cpus(), it did nothing about the similar deadlock involving acquisition of this same lock via put_online_cpus(). This deadlock became apparent with testing involving hibernation. This commit therefore changes put_online_cpus() acquisition of this lock to be conditional, and increments a new cpu_hotplug.puts_pending field in case of acquisition failure. Then cpu_hotplug_begin() checks for this new field being non-zero, and applies any changes to cpu_hotplug.refcount. Reported-by: Jiri Kosina <jkosina@suse.cz> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Tested-by: Jiri Kosina <jkosina@suse.cz> Tested-by: Borislav Petkov <bp@suse.de>
Diffstat (limited to 'kernel/cpu.c')
-rw-r--r--kernel/cpu.c14
1 files changed, 13 insertions, 1 deletions
diff --git a/kernel/cpu.c b/kernel/cpu.c
index 356450f09c1f..90a3d017b90c 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -64,6 +64,8 @@ static struct {
* an ongoing cpu hotplug operation.
*/
int refcount;
+ /* And allows lockless put_online_cpus(). */
+ atomic_t puts_pending;
#ifdef CONFIG_DEBUG_LOCK_ALLOC
struct lockdep_map dep_map;
@@ -113,7 +115,11 @@ void put_online_cpus(void)
{
if (cpu_hotplug.active_writer == current)
return;
- mutex_lock(&cpu_hotplug.lock);
+ if (!mutex_trylock(&cpu_hotplug.lock)) {
+ atomic_inc(&cpu_hotplug.puts_pending);
+ cpuhp_lock_release();
+ return;
+ }
if (WARN_ON(!cpu_hotplug.refcount))
cpu_hotplug.refcount++; /* try to fix things up */
@@ -155,6 +161,12 @@ void cpu_hotplug_begin(void)
cpuhp_lock_acquire();
for (;;) {
mutex_lock(&cpu_hotplug.lock);
+ if (atomic_read(&cpu_hotplug.puts_pending)) {
+ int delta;
+
+ delta = atomic_xchg(&cpu_hotplug.puts_pending, 0);
+ cpu_hotplug.refcount -= delta;
+ }
if (likely(!cpu_hotplug.refcount))
break;
__set_current_state(TASK_UNINTERRUPTIBLE);

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