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Commit 4f996e23 authored by Tejun Heo's avatar Tejun Heo
Browse files

percpu: fix synchronization between chunk->map_extend_work and chunk destruction 



Atomic allocations can trigger async map extensions which is serviced
by chunk->map_extend_work.  pcpu_balance_work which is responsible for
destroying idle chunks wasn't synchronizing properly against
chunk->map_extend_work and may end up freeing the chunk while the work
item is still in flight.

This patch fixes the bug by rolling async map extension operations
into pcpu_balance_work.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Reported-and-tested-by: default avatarAlexei Starovoitov <alexei.starovoitov@gmail.com>
Reported-by: default avatarVlastimil Babka <vbabka@suse.cz>
Reported-by: default avatarSasha Levin <sasha.levin@oracle.com>
Cc: stable@vger.kernel.org # v3.18+
Fixes: 9c824b6a ("percpu: make sure chunk->map array has available space")
parent 28165ec7

mm/percpu.c

+36 −21
Original line number Diff line number Diff line
@@ -112,7 +112,7 @@ struct pcpu_chunk { 
	int			map_used;	/* # of map entries used before the sentry */

	int			map_alloc;	/* # of map entries allocated */

	int			*map;		/* allocation map */

	struct work_struct	map_extend_work;/* async ->map[] extension */

	struct list_head	map_extend_list;/* on pcpu_map_extend_chunks */



	void			*data;		/* chunk data */

	int			first_free;	/* no free below this */
@@ -166,6 +166,9 @@ static DEFINE_MUTEX(pcpu_alloc_mutex); /* chunk create/destroy, [de]pop */ 


static struct list_head *pcpu_slot __read_mostly; /* chunk list slots */



/* chunks which need their map areas extended, protected by pcpu_lock */

static LIST_HEAD(pcpu_map_extend_chunks);



/*

 * The number of empty populated pages, protected by pcpu_lock.  The

 * reserved chunk doesn't contribute to the count.
@@ -395,13 +398,19 @@ static int pcpu_need_to_extend(struct pcpu_chunk *chunk, bool is_atomic) 
{

	int margin, new_alloc;



	lockdep_assert_held(&pcpu_lock);



	if (is_atomic) {

		margin = 3;



		if (chunk->map_alloc <

		    chunk->map_used + PCPU_ATOMIC_MAP_MARGIN_LOW &&

		    pcpu_async_enabled)

			schedule_work(&chunk->map_extend_work);

		    chunk->map_used + PCPU_ATOMIC_MAP_MARGIN_LOW) {

			if (list_empty(&chunk->map_extend_list)) {

				list_add_tail(&chunk->map_extend_list,

					      &pcpu_map_extend_chunks);

				pcpu_schedule_balance_work();

			}

		}

	} else {

		margin = PCPU_ATOMIC_MAP_MARGIN_HIGH;

	}
@@ -467,20 +476,6 @@ static int pcpu_extend_area_map(struct pcpu_chunk *chunk, int new_alloc) 
	return 0;

}



static void pcpu_map_extend_workfn(struct work_struct *work)

{

	struct pcpu_chunk *chunk = container_of(work, struct pcpu_chunk,

						map_extend_work);

	int new_alloc;



	spin_lock_irq(&pcpu_lock);

	new_alloc = pcpu_need_to_extend(chunk, false);

	spin_unlock_irq(&pcpu_lock);



	if (new_alloc)

		pcpu_extend_area_map(chunk, new_alloc);

}



/**

 * pcpu_fit_in_area - try to fit the requested allocation in a candidate area

 * @chunk: chunk the candidate area belongs to
@@ -740,7 +735,7 @@ static struct pcpu_chunk *pcpu_alloc_chunk(void) 
	chunk->map_used = 1;



	INIT_LIST_HEAD(&chunk->list);

	INIT_WORK(&chunk->map_extend_work, pcpu_map_extend_workfn);

	INIT_LIST_HEAD(&chunk->map_extend_list);

	chunk->free_size = pcpu_unit_size;

	chunk->contig_hint = pcpu_unit_size;
@@ -1129,6 +1124,7 @@ static void pcpu_balance_workfn(struct work_struct *work) 
		if (chunk == list_first_entry(free_head, struct pcpu_chunk, list))

			continue;



		list_del_init(&chunk->map_extend_list);

		list_move(&chunk->list, &to_free);

	}
@@ -1146,6 +1142,25 @@ static void pcpu_balance_workfn(struct work_struct *work) 
		pcpu_destroy_chunk(chunk);

	}



	/* service chunks which requested async area map extension */

	do {

		int new_alloc = 0;



		spin_lock_irq(&pcpu_lock);



		chunk = list_first_entry_or_null(&pcpu_map_extend_chunks,

					struct pcpu_chunk, map_extend_list);

		if (chunk) {

			list_del_init(&chunk->map_extend_list);

			new_alloc = pcpu_need_to_extend(chunk, false);

		}



		spin_unlock_irq(&pcpu_lock);



		if (new_alloc)

			pcpu_extend_area_map(chunk, new_alloc);

	} while (chunk);



	/*

	 * Ensure there are certain number of free populated pages for

	 * atomic allocs.  Fill up from the most packed so that atomic
@@ -1644,7 +1659,7 @@ int __init pcpu_setup_first_chunk(const struct pcpu_alloc_info *ai, 
	 */

	schunk = memblock_virt_alloc(pcpu_chunk_struct_size, 0);

	INIT_LIST_HEAD(&schunk->list);

	INIT_WORK(&schunk->map_extend_work, pcpu_map_extend_workfn);

	INIT_LIST_HEAD(&schunk->map_extend_list);

	schunk->base_addr = base_addr;

	schunk->map = smap;

	schunk->map_alloc = ARRAY_SIZE(smap);
@@ -1673,7 +1688,7 @@ int __init pcpu_setup_first_chunk(const struct pcpu_alloc_info *ai, 
	if (dyn_size) {

		dchunk = memblock_virt_alloc(pcpu_chunk_struct_size, 0);

		INIT_LIST_HEAD(&dchunk->list);

		INIT_WORK(&dchunk->map_extend_work, pcpu_map_extend_workfn);

		INIT_LIST_HEAD(&dchunk->map_extend_list);

		dchunk->base_addr = base_addr;

		dchunk->map = dmap;

		dchunk->map_alloc = ARRAY_SIZE(dmap);