The patch titled
Subject: mm: lru_cache_disable: replace work queue synchronization with synchronize_rcu
has been added to the -mm tree. Its filename is
mm-lru_cache_disable-replace-work-queue-synchronization-with-synchronize_rcu.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/mm-lru_cache_disable-replace-work-queue-synchronization-with-synchronize_rcu.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/mm-lru_cache_disable-replace-work-queue-synchronization-with-synchronize_rcu.patch
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------------------------------------------------------
From: Marcelo Tosatti <mtosatti@xxxxxxxxxx>
Subject: mm: lru_cache_disable: replace work queue synchronization with synchronize_rcu
On systems that run FIFO:1 applications that busy loop, any SCHED_OTHER
task that attempts to execute on such a CPU (such as work threads) will
not be scheduled, which leads to system hangs.
Commit d479960e44f27e0e5 ("mm: disable LRU pagevec during the migration
temporarily") relies on queueing work items on all online CPUs to ensure
visibility of lru_disable_count.
To fix this, replace the usage of work items with synchronize_rcu,
which provides the same guarantees.
Readers of lru_disable_count are protected by either disabling
preemption or rcu_read_lock:
preempt_disable, local_irq_disable [bh_lru_lock()]
rcu_read_lock [rt_spin_lock CONFIG_PREEMPT_RT]
preempt_disable [local_lock !CONFIG_PREEMPT_RT]
Since v5.1 kernel, synchronize_rcu() is guaranteed to wait on
preempt_disable() regions of code. So any CPU which sees
lru_disable_count = 0 will have exited the critical section when
synchronize_rcu() returns.
Link: https://lkml.kernel.org/r/Yin7hDxdt0s/x+fp@xxxxxxxxxxx
Signed-off-by: Marcelo Tosatti <mtosatti@xxxxxxxxxx>
Reviewed-by: Nicolas Saenz Julienne <nsaenzju@xxxxxxxxxx>
Acked-by: Minchan Kim <minchan@xxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Cc: Juri Lelli <juri.lelli@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Cc: Paul E. McKenney <paulmck@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/swap.c | 23 ++++++++++++++---------
1 file changed, 14 insertions(+), 9 deletions(-)
--- a/mm/swap.c~mm-lru_cache_disable-replace-work-queue-synchronization-with-synchronize_rcu
+++ a/mm/swap.c
@@ -831,8 +831,7 @@ inline void __lru_add_drain_all(bool for
for_each_online_cpu(cpu) {
struct work_struct *work = &per_cpu(lru_add_drain_work, cpu);
- if (force_all_cpus ||
- pagevec_count(&per_cpu(lru_pvecs.lru_add, cpu)) ||
+ if (pagevec_count(&per_cpu(lru_pvecs.lru_add, cpu)) ||
data_race(pagevec_count(&per_cpu(lru_rotate.pvec, cpu))) ||
pagevec_count(&per_cpu(lru_pvecs.lru_deactivate_file, cpu)) ||
pagevec_count(&per_cpu(lru_pvecs.lru_deactivate, cpu)) ||
@@ -876,15 +875,21 @@ atomic_t lru_disable_count = ATOMIC_INIT
void lru_cache_disable(void)
{
atomic_inc(&lru_disable_count);
-#ifdef CONFIG_SMP
/*
- * lru_add_drain_all in the force mode will schedule draining on
- * all online CPUs so any calls of lru_cache_disabled wrapped by
- * local_lock or preemption disabled would be ordered by that.
- * The atomic operation doesn't need to have stronger ordering
- * requirements because that is enforced by the scheduling
- * guarantees.
+ * Readers of lru_disable_count are protected by either disabling
+ * preemption or rcu_read_lock:
+ *
+ * preempt_disable, local_irq_disable [bh_lru_lock()]
+ * rcu_read_lock [rt_spin_lock CONFIG_PREEMPT_RT]
+ * preempt_disable [local_lock !CONFIG_PREEMPT_RT]
+ *
+ * Since v5.1 kernel, synchronize_rcu() is guaranteed to wait on
+ * preempt_disable() regions of code. So any CPU which sees
+ * lru_disable_count = 0 will have exited the critical
+ * section when synchronize_rcu() returns.
*/
+ synchronize_rcu();
+#ifdef CONFIG_SMP
__lru_add_drain_all(true);
#else
lru_add_and_bh_lrus_drain();
_
Patches currently in -mm which might be from mtosatti@xxxxxxxxxx are
mm-lru_cache_disable-replace-work-queue-synchronization-with-synchronize_rcu.patch
