zswap: allow initialization at boot without pool

Allow zswap to initialize at boot even if it can't create its pool due
to a failure to create a zpool and/or compressor.  Allow those to be
created later, from the sysfs module param interface.

Link: http://lkml.kernel.org/r/20170124200259.16191-3-ddstreet@ieee.org
Signed-off-by: Dan Streetman <dan.streetman@canonical.com>
Cc: Seth Jennings <sjenning@redhat.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Cc: Minchan Kim <minchan@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 34 insertions, 12 deletions

diff --git a/mm/zswap.c b/mm/zswap.c
index cabf09e0128b..77cb847938e1 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -185,6 +185,9 @@ static bool zswap_init_started;
 /* fatal error during init */
 static bool zswap_init_failed;
 
+/* init completed, but couldn't create the initial pool */
+static bool zswap_has_pool;
+
 /*********************************
 * helpers and fwd declarations
 **********************************/
@@ -424,7 +427,8 @@ static struct zswap_pool *__zswap_pool_current(void)
         struct zswap_pool *pool;
 
         pool = list_first_or_null_rcu(&zswap_pools, typeof(*pool), list);
-        WARN_ON(!pool);
+        WARN_ONCE(!pool && zswap_has_pool,
+                  "%s: no page storage pool!\n", __func__);
 
         return pool;
 }
@@ -443,7 +447,7 @@ static struct zswap_pool *zswap_pool_current_get(void)
         rcu_read_lock();
 
         pool = __zswap_pool_current();
-        if (!pool || !zswap_pool_get(pool))
+        if (!zswap_pool_get(pool))
                 pool = NULL;
 
         rcu_read_unlock();
@@ -459,7 +463,9 @@ static struct zswap_pool *zswap_pool_last_get(void)
 
         list_for_each_entry_rcu(pool, &zswap_pools, list)
                 last = pool;
-        if (!WARN_ON(!last) && !zswap_pool_get(last))
+        WARN_ONCE(!last && zswap_has_pool,
+                  "%s: no page storage pool!\n", __func__);
+        if (!zswap_pool_get(last))
                 last = NULL;
 
         rcu_read_unlock();
@@ -582,6 +588,9 @@ static void zswap_pool_destroy(struct zswap_pool *pool)
 
 static int __must_check zswap_pool_get(struct zswap_pool *pool)
 {
+        if (!pool)
+                return 0;
+
         return kref_get_unless_zero(&pool->kref);
 }
 
@@ -639,7 +648,7 @@ static int __zswap_param_set(const char *val, const struct kernel_param *kp,
         }
 
         /* no change required */
-        if (!strcmp(s, *(char **)kp->arg))
+        if (!strcmp(s, *(char **)kp->arg) && zswap_has_pool)
                 return 0;
 
         /* if this is load-time (pre-init) param setting,
@@ -685,6 +694,7 @@ static int __zswap_param_set(const char *val, const struct kernel_param *kp,
         if (!ret) {
                 put_pool = zswap_pool_current();
                 list_add_rcu(&pool->list, &zswap_pools);
+                zswap_has_pool = true;
         } else if (pool) {
                 /* add the possibly pre-existing pool to the end of the pools
                  * list; if it's new (and empty) then it'll be removed and
@@ -692,6 +702,15 @@ static int __zswap_param_set(const char *val, const struct kernel_param *kp,
                  */
                 list_add_tail_rcu(&pool->list, &zswap_pools);
                 put_pool = pool;
+        } else if (!zswap_has_pool) {
+                /* if initial pool creation failed, and this pool creation also
+                 * failed, maybe both compressor and zpool params were bad.
+                 * Allow changing this param, so pool creation will succeed
+                 * when the other param is changed. We already verified this
+                 * param is ok in the zpool_has_pool() or crypto_has_comp()
+                 * checks above.
+                 */
+                ret = param_set_charp(s, kp);
         }
 
         spin_unlock(&zswap_pools_lock);
@@ -724,6 +743,10 @@ static int zswap_enabled_param_set(const char *val,
                 pr_err("can't enable, initialization failed\n");
                 return -ENODEV;
         }
+        if (!zswap_has_pool && zswap_init_started) {
+                pr_err("can't enable, no pool configured\n");
+                return -ENODEV;
+        }
 
         return param_set_bool(val, kp);
 }
@@ -1205,22 +1228,21 @@ static int __init init_zswap(void)
                 goto hp_fail;
 
         pool = __zswap_pool_create_fallback();
-        if (!pool) {
+        if (pool) {
+                pr_info("loaded using pool %s/%s\n", pool->tfm_name,
+                        zpool_get_type(pool->zpool));
+                list_add(&pool->list, &zswap_pools);
+                zswap_has_pool = true;
+        } else {
                 pr_err("pool creation failed\n");
-                goto pool_fail;
+                zswap_enabled = false;
         }
-        pr_info("loaded using pool %s/%s\n", pool->tfm_name,
-                zpool_get_type(pool->zpool));
-
-        list_add(&pool->list, &zswap_pools);
 
         frontswap_register_ops(&zswap_frontswap_ops);
         if (zswap_debugfs_init())
                 pr_warn("debugfs initialization failed\n");
         return 0;
 
-pool_fail:
-        cpuhp_remove_state_nocalls(CPUHP_MM_ZSWP_POOL_PREPARE);
 hp_fail:
         cpuhp_remove_state(CPUHP_MM_ZSWP_MEM_PREPARE);
 dstmem_fail: