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

With the original commit applied, z3fold_zpool_destroy() may get blocked
on wait_event() for indefinite time.  Revert this commit for the time
being to get rid of this problem since the issue the original commit
addresses is less severe.

Link: http://lkml.kernel.org/r/20190910123142.7a9c8d2de4d0acbc0977c602@gmail.com
Fixes: d776aaa9895eb6eb77 ("mm/z3fold.c: fix race between migration and destruction")
Reported-by: Agustín Dall'Alba <agustin@dallalba.com.ar>
Signed-off-by: Vitaly Wool <vitalywool@gmail.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
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: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/z3fold.c b/mm/z3fold.c
index 75b7962..ed19d98 100644 (file)
--- a/mm/z3fold.c
+++ b/mm/z3fold.c
@@ -41,7 +41,6 @@
 #include <linux/workqueue.h>
 #include <linux/slab.h>
 #include <linux/spinlock.h>
-#include <linux/wait.h>
 #include <linux/zpool.h>
 #include <linux/magic.h>
 
@@ -146,8 +145,6 @@ 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.
@@ -166,11 +163,8 @@ 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;
 };
 
 /*
@@ -775,7 +769,6 @@ 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;
@@ -815,15 +808,6 @@ out:
        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
@@ -833,22 +817,6 @@ static bool pool_isolated_are_drained(struct z3fold_pool *pool)
 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,
@@ -1339,28 +1307,6 @@ 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;
@@ -1387,34 +1333,6 @@ 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");
-                               z3fold_page_unlock(zhdr);
-                               return false;
-                       }
-                       z3fold_page_unlock(zhdr);
-                       return false;
-               }
-
-
-               z3fold_inc_isolated(pool);
                spin_unlock(&pool->lock);
                z3fold_page_unlock(zhdr);
                return true;
@@ -1483,10 +1401,6 @@ 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;
@@ -1506,14 +1420,10 @@ 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);
 }