[PATCH 4.4 066/146] percpu: fix synchronization between chunk->map_extend_work and chunk destruction

Greg Kroah-Hartman
2016-07-25T22:42:43Z

From: Tejun Heo <tj@kernel.org>

commit 4f996e234dad488e5d9ba0858bc1bae12eff82c3 upstream.

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: Tejun Heo <tj@kernel.org>
Reported-and-tested-by: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Reported-by: Vlastimil Babka <vbabka@suse.cz>
Reported-by: Sasha Levin <sasha.levin@oracle.com>
Fixes: 9c824b6a172c ("percpu: make sure chunk->map array has available space")
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
mm/percpu.c | 57 ++++++++++++++++++++++++++++++++++++---------------------
1 file changed, 36 insertions(+), 21 deletions(-)

--- a/mm/percpu.c
+++ b/mm/percpu.c
@@ -110,7 +110,7 @@ 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 */
@@ -164,6 +164,9 @@ static DEFINE_MUTEX(pcpu_alloc_mutex); /

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.
@@ -397,13 +400,19 @@ static int pcpu_need_to_extend(struct pc
{
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;
}
@@ -469,20 +478,6 @@ out_unlock:
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
@@ -742,7 +737,7 @@ static struct pcpu_chunk *pcpu_alloc_chu
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;

@@ -1131,6 +1126,7 @@ static void pcpu_balance_workfn(struct w
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);
}

@@ -1148,6 +1144,25 @@ static void pcpu_balance_workfn(struct w
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
@@ -1646,7 +1661,7 @@ int __init pcpu_setup_first_chunk(const
*/
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);
@@ -1675,7 +1690,7 @@ int __init pcpu_setup_first_chunk(const
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);