Commit d776aaa9 authored by Henry Burns's avatar Henry Burns Committed by Linus Torvalds
Browse files

mm/z3fold.c: fix race between migration and destruction

In z3fold_destroy_pool() we call destroy_workqueue(&pool->compact_wq).
However, we have no guarantee that migration isn't happening in the
background at that time.

Migration directly calls queue_work_on(pool->compact_wq), if destruction
wins that race we are using a destroyed workqueue.

Link: http://lkml.kernel.org/r/20190809213828.202833-1-henryburns@google.com

Signed-off-by: default avatarHenry Burns <henryburns@google.com>
Cc: Vitaly Wool <vitalywool@gmail.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Jonathan Adams <jwadams@google.com>
Cc: Henry Burns <henrywolfeburns@gmail.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 36146921
......@@ -41,6 +41,7 @@
#include <linux/workqueue.h>
#include <linux/slab.h>
#include <linux/spinlock.h>
#include <linux/wait.h>
#include <linux/zpool.h>
#include <linux/magic.h>
......@@ -145,6 +146,8 @@ struct z3fold_header {
* @release_wq: workqueue for safe page release
* @work: work_struct for safe page release
* @inode: inode for z3fold pseudo filesystem
* @destroying: bool to stop migration once we start destruction
* @isolated: int to count the number of pages currently in isolation
*
* This structure is allocated at pool creation time and maintains metadata
* pertaining to a particular z3fold pool.
......@@ -163,8 +166,11 @@ struct z3fold_pool {
const struct zpool_ops *zpool_ops;
struct workqueue_struct *compact_wq;
struct workqueue_struct *release_wq;
struct wait_queue_head isolate_wait;
struct work_struct work;
struct inode *inode;
bool destroying;
int isolated;
};
/*
......@@ -769,6 +775,7 @@ static struct z3fold_pool *z3fold_create_pool(const char *name, gfp_t gfp,
goto out_c;
spin_lock_init(&pool->lock);
spin_lock_init(&pool->stale_lock);
init_waitqueue_head(&pool->isolate_wait);
pool->unbuddied = __alloc_percpu(sizeof(struct list_head)*NCHUNKS, 2);
if (!pool->unbuddied)
goto out_pool;
......@@ -808,6 +815,15 @@ static struct z3fold_pool *z3fold_create_pool(const char *name, gfp_t gfp,
return NULL;
}
static bool pool_isolated_are_drained(struct z3fold_pool *pool)
{
bool ret;
spin_lock(&pool->lock);
ret = pool->isolated == 0;
spin_unlock(&pool->lock);
return ret;
}
/**
* z3fold_destroy_pool() - destroys an existing z3fold pool
* @pool: the z3fold pool to be destroyed
......@@ -817,6 +833,22 @@ static struct z3fold_pool *z3fold_create_pool(const char *name, gfp_t gfp,
static void z3fold_destroy_pool(struct z3fold_pool *pool)
{
kmem_cache_destroy(pool->c_handle);
/*
* We set pool-> destroying under lock to ensure that
* z3fold_page_isolate() sees any changes to destroying. This way we
* avoid the need for any memory barriers.
*/
spin_lock(&pool->lock);
pool->destroying = true;
spin_unlock(&pool->lock);
/*
* We need to ensure that no pages are being migrated while we destroy
* these workqueues, as migration can queue work on either of the
* workqueues.
*/
wait_event(pool->isolate_wait, !pool_isolated_are_drained(pool));
/*
* We need to destroy pool->compact_wq before pool->release_wq,
......@@ -1307,6 +1339,28 @@ static u64 z3fold_get_pool_size(struct z3fold_pool *pool)
return atomic64_read(&pool->pages_nr);
}
/*
* z3fold_dec_isolated() expects to be called while pool->lock is held.
*/
static void z3fold_dec_isolated(struct z3fold_pool *pool)
{
assert_spin_locked(&pool->lock);
VM_BUG_ON(pool->isolated <= 0);
pool->isolated--;
/*
* If we have no more isolated pages, we have to see if
* z3fold_destroy_pool() is waiting for a signal.
*/
if (pool->isolated == 0 && waitqueue_active(&pool->isolate_wait))
wake_up_all(&pool->isolate_wait);
}
static void z3fold_inc_isolated(struct z3fold_pool *pool)
{
pool->isolated++;
}
static bool z3fold_page_isolate(struct page *page, isolate_mode_t mode)
{
struct z3fold_header *zhdr;
......@@ -1333,6 +1387,33 @@ static bool z3fold_page_isolate(struct page *page, isolate_mode_t mode)
spin_lock(&pool->lock);
if (!list_empty(&page->lru))
list_del(&page->lru);
/*
* We need to check for destruction while holding pool->lock, as
* otherwise destruction could see 0 isolated pages, and
* proceed.
*/
if (unlikely(pool->destroying)) {
spin_unlock(&pool->lock);
/*
* If this page isn't stale, somebody else holds a
* reference to it. Let't drop our refcount so that they
* can call the release logic.
*/
if (unlikely(kref_put(&zhdr->refcount,
release_z3fold_page_locked))) {
/*
* If we get here we have kref problems, so we
* should freak out.
*/
WARN(1, "Z3fold is experiencing kref problems\n");
return false;
}
z3fold_page_unlock(zhdr);
return false;
}
z3fold_inc_isolated(pool);
spin_unlock(&pool->lock);
z3fold_page_unlock(zhdr);
return true;
......@@ -1401,6 +1482,10 @@ static int z3fold_page_migrate(struct address_space *mapping, struct page *newpa
queue_work_on(new_zhdr->cpu, pool->compact_wq, &new_zhdr->work);
spin_lock(&pool->lock);
z3fold_dec_isolated(pool);
spin_unlock(&pool->lock);
page_mapcount_reset(page);
put_page(page);
return 0;
......@@ -1420,10 +1505,14 @@ static void z3fold_page_putback(struct page *page)
INIT_LIST_HEAD(&page->lru);
if (kref_put(&zhdr->refcount, release_z3fold_page_locked)) {
atomic64_dec(&pool->pages_nr);
spin_lock(&pool->lock);
z3fold_dec_isolated(pool);
spin_unlock(&pool->lock);
return;
}
spin_lock(&pool->lock);
list_add(&page->lru, &pool->lru);
z3fold_dec_isolated(pool);
spin_unlock(&pool->lock);
z3fold_page_unlock(zhdr);
}
......
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