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authorMarcelo Tosatti <mtosatti@redhat.com>2022-03-22 14:45:47 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2022-03-22 15:57:08 -0700
commitff042f4a9b050895a42cae893cc01fa2ca81b95c (patch)
tree420e18ca40e3ed944a162adf315425bc04e69a20
parent405cc51fc1049c73ae03ce3771a2511a7cf8b240 (diff)
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@fuller.cnet Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com> Reviewed-by: Nicolas Saenz Julienne <nsaenzju@redhat.com> Acked-by: Minchan Kim <minchan@kernel.org> Cc: Matthew Wilcox <willy@infradead.org> Cc: Mel Gorman <mgorman@techsingularity.net> Cc: Juri Lelli <juri.lelli@redhat.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Cc: Paul E. McKenney <paulmck@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--mm/swap.c23
1 files changed, 14 insertions, 9 deletions
diff --git a/mm/swap.c b/mm/swap.c
index e9786c4f36d8..754520bab299 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -831,8 +831,7 @@ inline void __lru_add_drain_all(bool force_all_cpus)
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(0);
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();