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authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2012-10-07 19:36:12 +0400
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2012-10-08 20:06:38 +0400
commita4fbe35a124526e6759be07bd9c7ea796ba1e00d (patch)
treecb5c5a1608fcff588ed9a204ea67d5891adb18fb /kernel/rcutree.h
parentcb349ca95407cbc11424d5e9fc7c8e700709041b (diff)
downloadlinux-a4fbe35a124526e6759be07bd9c7ea796ba1e00d.tar.xz
rcu: Grace-period initialization excludes only RCU notifier
Kirill noted the following deadlock cycle on shutdown involving padata: > With commit 755609a9087fa983f567dc5452b2fa7b089b591f I've got deadlock on > poweroff. > > It guess it happens because of race for cpu_hotplug.lock: > > CPU A CPU B > disable_nonboot_cpus() > _cpu_down() > cpu_hotplug_begin() > mutex_lock(&cpu_hotplug.lock); > __cpu_notify() > padata_cpu_callback() > __padata_remove_cpu() > padata_replace() > synchronize_rcu() > rcu_gp_kthread() > get_online_cpus(); > mutex_lock(&cpu_hotplug.lock); It would of course be good to eliminate grace-period delays from CPU-hotplug notifiers, but that is a separate issue. Deadlock is not an appropriate diagnostic for excessive CPU-hotplug latency. Fortunately, grace-period initialization does not actually need to exclude all of the CPU-hotplug operation, but rather only RCU's own CPU_UP_PREPARE and CPU_DEAD CPU-hotplug notifiers. This commit therefore introduces a new per-rcu_state onoff_mutex that provides the required concurrency control in place of the get_online_cpus() that was previously in rcu_gp_init(). Reported-by: "Kirill A. Shutemov" <kirill@shutemov.name> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Tested-by: Kirill A. Shutemov <kirill@shutemov.name>
Diffstat (limited to 'kernel/rcutree.h')
-rw-r--r--kernel/rcutree.h6
1 files changed, 6 insertions, 0 deletions
diff --git a/kernel/rcutree.h b/kernel/rcutree.h
index 5faf05d68326..a240f032848e 100644
--- a/kernel/rcutree.h
+++ b/kernel/rcutree.h
@@ -394,11 +394,17 @@ struct rcu_state {
struct rcu_head **orphan_donetail; /* Tail of above. */
long qlen_lazy; /* Number of lazy callbacks. */
long qlen; /* Total number of callbacks. */
+ /* End of fields guarded by onofflock. */
+
+ struct mutex onoff_mutex; /* Coordinate hotplug & GPs. */
+
struct mutex barrier_mutex; /* Guards barrier fields. */
atomic_t barrier_cpu_count; /* # CPUs waiting on. */
struct completion barrier_completion; /* Wake at barrier end. */
unsigned long n_barrier_done; /* ++ at start and end of */
/* _rcu_barrier(). */
+ /* End of fields guarded by barrier_mutex. */
+
unsigned long jiffies_force_qs; /* Time at which to invoke */
/* force_quiescent_state(). */
unsigned long n_force_qs; /* Number of calls to */