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Date: Tue, 10 Sep 2019 13:19:04 +0200
From: Vlastimil Babka <vbabka@...e.cz>
To: Vitaly Wool <vitalywool@...il.com>, Linux-MM <linux-mm@...ck.org>,
linux-kernel@...r.kernel.org
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Agustín Dall'Alba <agustin@...lalba.com.ar>,
Henry Burns <henrywolfeburns@...il.com>,
Linus Torvalds <torvalds@...ux-foundation.org>,
stable <stable@...r.kernel.org>
Subject: Re: [PATCH] Revert "mm/z3fold.c: fix race between migration and
destruction"
On 9/10/19 12:31 PM, Vitaly Wool wrote:
> 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.
>
> This reverts commit d776aaa9895eb6eb770908e899cb7f5bd5025b3c.
Let's make it clear that the revert should go to 5.3 immediately,
because the commit above was introduced before 5.3-rc6.
> Reported-by: Agustín Dall'Alba <agustin@...lalba.com.ar>
> Signed-off-by: Vitaly Wool <vitalywool@...il.com>
Fixes: d776aaa9895e ("mm/z3fold.c: fix race between migration and
destruction")
Cc: stable <stable@...r.kernel.org>
d776aaa9895e was Cc: stable, so if stable kernels picked it up, they
should pick the revert as well.
> ---
> mm/z3fold.c | 90 -----------------------------------------------------
> 1 file changed, 90 deletions(-)
>
> diff --git a/mm/z3fold.c b/mm/z3fold.c
> index 75b7962439ff..ed19d98c9dcd 100644
> --- 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 @@ 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
> @@ -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);
> }
>
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