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Subject[PATCH 5.2 22/45] Revert "mm/z3fold.c: fix race between migration and destruction"
Date
From: Vitaly Wool <vitalywool@gmail.com>

commit 6e73fd25e2c7510b7dfadbaf701f31d4bff9c75b upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
mm/z3fold.c | 90 ------------------------------------------------------------
1 file changed, 90 deletions(-)

--- 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>

/*
@@ -145,8 +144,6 @@ 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.
@@ -165,11 +162,8 @@ 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;
};

/*
@@ -777,7 +771,6 @@ static struct z3fold_pool *z3fold_create
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;
@@ -817,15 +810,6 @@ 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
@@ -835,22 +819,6 @@ static bool pool_isolated_are_drained(st
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,
@@ -1341,28 +1309,6 @@ static u64 z3fold_get_pool_size(struct z
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;
@@ -1389,34 +1335,6 @@ static bool z3fold_page_isolate(struct p
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;
@@ -1485,10 +1403,6 @@ static int z3fold_page_migrate(struct ad

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;
@@ -1508,14 +1422,10 @@ static void z3fold_page_putback(struct p
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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