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. Signed-off-by: Henry Burns <henrybu...@google.com> --- mm/z3fold.c | 51 +++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 51 insertions(+) diff --git a/mm/z3fold.c b/mm/z3fold.c index 78447cecfffa..e136d97ce56e 100644 --- a/mm/z3fold.c +++ b/mm/z3fold.c @@ -40,6 +40,7 @@ #include <linux/workqueue.h> #include <linux/slab.h> #include <linux/spinlock.h> +#include <linux/wait.h> #include <linux/zpool.h> /* @@ -161,8 +162,10 @@ 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; + int isolated_pages; }; /* @@ -772,6 +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; @@ -811,6 +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_pages == 0; + spin_unlock(&pool->lock); + return ret; +} /** * z3fold_destroy_pool() - destroys an existing z3fold pool * @pool: the z3fold pool to be destroyed @@ -821,6 +834,13 @@ static void z3fold_destroy_pool(struct z3fold_pool *pool) { kmem_cache_destroy(pool->c_handle); + /* + * 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, * as any pending work on pool->compact_wq will call @@ -1317,6 +1337,28 @@ 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_pages <= 0); + pool->isolated_pages--; + + /* + * If we have no more isolated pages, we have to see if + * z3fold_destroy_pool() is waiting for a signal. + */ + if (pool->isolated_pages == 0 && waitqueue_active(&pool->isolate_wait)) + wake_up_all(&pool->isolate_wait); +} + +static void z3fold_inc_isolated(struct z3fold_pool *pool) +{ + pool->isolated_pages++; +} + static bool z3fold_page_isolate(struct page *page, isolate_mode_t mode) { struct z3fold_header *zhdr; @@ -1343,6 +1385,7 @@ 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); + z3fold_inc_isolated(pool); spin_unlock(&pool->lock); z3fold_page_unlock(zhdr); return true; @@ -1417,6 +1460,10 @@ 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; @@ -1436,10 +1483,14 @@ 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); } -- 2.22.0.770.g0f2c4a37fd-goog