Commit 9852a721 authored Jan 31, 2018 by Michal Hocko Committed by Linus Torvalds Jan 31, 2018

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 a459eeb7 ("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>

parent 0486a38b

include/linux/swap.h

+0 −1

Original line number	Diff line number	Diff line
		@@ -332,7 +332,6 @@ extern void mark_page_accessed(struct page *);
		extern void lru_add_drain(void);
		extern void lru_add_drain_cpu(int cpu);
		extern void lru_add_drain_all(void);
		extern void lru_add_drain_all_cpuslocked(void);
		extern void rotate_reclaimable_page(struct page *page);
		extern void deactivate_file_page(struct page *page);
		extern void mark_page_lazyfree(struct page *page);

mm/memory_hotplug.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -1637,7 +1637,7 @@ repeat:
		goto failed_removal;

		cond_resched();
		lru_add_drain_all_cpuslocked();
		lru_add_drain_all();
		drain_all_pages(zone);

		pfn = scan_movable_pages(start_pfn, end_pfn);

mm/swap.c

+8 −8

Original line number	Diff line number	Diff line
		@@ -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

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