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authorMichal Hocko <mhocko@suse.com>2018-01-31 16:16:19 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2018-01-31 17:18:36 -0800
commit9852a7212324fd25f896932f4f4607ce47b0a22f (patch)
tree83203a3d766a4e72a1c087eea9ea7e089aab122e /mm/swap.c
parent0486a38bcc4749808edbc848f1bcf232042770fc (diff)
mm: drop hotplug lock from lru_add_drain_all()
Pulling cpu hotplug locks inside the mm core function like lru_add_drain_all just asks for problems and the recent lockdep splat [1] just proves this. While the usage in that particular case might be wrong we should avoid the locking as lru_add_drain_all() is used in many places. It seems that this is not all that hard to achieve actually. We have done the same thing for drain_all_pages which is analogous by commit a459eeb7b852 ("mm, page_alloc: do not depend on cpu hotplug locks inside the allocator"). All we have to care about is to handle - the work item might be executed on a different cpu in worker from unbound pool so it doesn't run on pinned on the cpu - we have to make sure that we do not race with page_alloc_cpu_dead calling lru_add_drain_cpu the first part is already handled because the worker calls lru_add_drain which disables preemption when calling lru_add_drain_cpu on the local cpu it is draining. The later is true because page_alloc_cpu_dead is called on the controlling CPU after the hotplugged CPU vanished completely. [1] http://lkml.kernel.org/r/089e0825eec8955c1f055c83d476@google.com [add a cpu hotplug locking interaction as per tglx] Link: http://lkml.kernel.org/r/20171116120535.23765-1-mhocko@kernel.org Signed-off-by: Michal Hocko <mhocko@suse.com> Acked-by: Thomas Gleixner <tglx@linutronix.de> Cc: Tejun Heo <tj@kernel.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Mel Gorman <mgorman@suse.de> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/swap.c')
-rw-r--r--mm/swap.c16
1 files changed, 8 insertions, 8 deletions
diff --git a/mm/swap.c b/mm/swap.c
index 38e1b6374a97..e824c800adca 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -688,7 +688,14 @@ static void lru_add_drain_per_cpu(struct work_struct *dummy)
static DEFINE_PER_CPU(struct work_struct, lru_add_drain_work);
-void lru_add_drain_all_cpuslocked(void)
+/*
+ * Doesn't need any cpu hotplug locking because we do rely on per-cpu
+ * kworkers being shut down before our page_alloc_cpu_dead callback is
+ * executed on the offlined cpu.
+ * Calling this function with cpu hotplug locks held can actually lead
+ * to obscure indirect dependencies via WQ context.
+ */
+void lru_add_drain_all(void)
{
static DEFINE_MUTEX(lock);
static struct cpumask has_work;
@@ -724,13 +731,6 @@ void lru_add_drain_all_cpuslocked(void)
mutex_unlock(&lock);
}
-void lru_add_drain_all(void)
-{
- get_online_cpus();
- lru_add_drain_all_cpuslocked();
- put_online_cpus();
-}
-
/**
* release_pages - batched put_page()
* @pages: array of pages to release