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Commit 9852a721 authored by Michal Hocko's avatar Michal Hocko Committed by Linus Torvalds
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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: default avatarMichal Hocko <mhocko@suse.com>
Acked-by: default avatarThomas 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: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus 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 @@ static int __ref __offline_pages(unsigned long start_pfn, 
		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