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Merge branch 'for-4.7-fixes' of git://git.kernel.org/pub/scm/linux/ke…
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…rnel/git/tj/percpu

Pull percpu fixes from Tejun Heo:
 "While adding GFP_ATOMIC support to the percpu allocator, the
  synchronization for the fast-path which doesn't require external
  allocations was separated into pcpu_lock.

  Unfortunately, it incorrectly decoupled async paths and percpu
  chunks could get destroyed while still being operated on.  This
  contains two patches to fix the bug"

* 'for-4.7-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/percpu:
  percpu: fix synchronization between synchronous map extension and chunk destruction
  percpu: fix synchronization between chunk->map_extend_work and chunk destruction
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@torvalds
torvalds committed Jun 14, 2016
2 parents 35398ee + 6710e59 commit db06d75
Showing 1 changed file with 44 additions and 29 deletions.
73 changes: 44 additions & 29 deletions mm/percpu.c
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Original file line number Diff line number Diff line change
Expand Up @@ -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 */
Expand Down Expand Up @@ -162,10 +162,13 @@ static struct pcpu_chunk *pcpu_reserved_chunk;
static int pcpu_reserved_chunk_limit;

static DEFINE_SPINLOCK(pcpu_lock); /* all internal data structures */
static DEFINE_MUTEX(pcpu_alloc_mutex); /* chunk create/destroy, [de]pop */
static DEFINE_MUTEX(pcpu_alloc_mutex); /* chunk create/destroy, [de]pop, map ext */

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.
Expand Down Expand Up @@ -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;
}
Expand Down Expand Up @@ -435,6 +444,8 @@ static int pcpu_extend_area_map(struct pcpu_chunk *chunk, int new_alloc)
size_t old_size = 0, new_size = new_alloc * sizeof(new[0]);
unsigned long flags;

lockdep_assert_held(&pcpu_alloc_mutex);

new = pcpu_mem_zalloc(new_size);
if (!new)
return -ENOMEM;
Expand Down Expand Up @@ -467,20 +478,6 @@ 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
Expand Down Expand Up @@ -740,7 +737,7 @@ 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;

Expand Down Expand Up @@ -895,6 +892,9 @@ static void __percpu *pcpu_alloc(size_t size, size_t align, bool reserved,
return NULL;
}

if (!is_atomic)
mutex_lock(&pcpu_alloc_mutex);

spin_lock_irqsave(&pcpu_lock, flags);

/* serve reserved allocations from the reserved chunk if available */
Expand Down Expand Up @@ -967,12 +967,9 @@ static void __percpu *pcpu_alloc(size_t size, size_t align, bool reserved,
if (is_atomic)
goto fail;

mutex_lock(&pcpu_alloc_mutex);

if (list_empty(&pcpu_slot[pcpu_nr_slots - 1])) {
chunk = pcpu_create_chunk();
if (!chunk) {
mutex_unlock(&pcpu_alloc_mutex);
err = "failed to allocate new chunk";
goto fail;
}
Expand All @@ -983,7 +980,6 @@ static void __percpu *pcpu_alloc(size_t size, size_t align, bool reserved,
spin_lock_irqsave(&pcpu_lock, flags);
}

mutex_unlock(&pcpu_alloc_mutex);
goto restart;

area_found:
Expand All @@ -993,8 +989,6 @@ static void __percpu *pcpu_alloc(size_t size, size_t align, bool reserved,
if (!is_atomic) {
int page_start, page_end, rs, re;

mutex_lock(&pcpu_alloc_mutex);

page_start = PFN_DOWN(off);
page_end = PFN_UP(off + size);

Expand All @@ -1005,7 +999,6 @@ static void __percpu *pcpu_alloc(size_t size, size_t align, bool reserved,

spin_lock_irqsave(&pcpu_lock, flags);
if (ret) {
mutex_unlock(&pcpu_alloc_mutex);
pcpu_free_area(chunk, off, &occ_pages);
err = "failed to populate";
goto fail_unlock;
Expand Down Expand Up @@ -1045,6 +1038,8 @@ static void __percpu *pcpu_alloc(size_t size, size_t align, bool reserved,
/* see the flag handling in pcpu_blance_workfn() */
pcpu_atomic_alloc_failed = true;
pcpu_schedule_balance_work();
} else {
mutex_unlock(&pcpu_alloc_mutex);
}
return NULL;
}
Expand Down Expand Up @@ -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);
}

Expand All @@ -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
Expand Down Expand Up @@ -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);
Expand Down Expand Up @@ -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);
Expand Down

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