Re: scheduling while atomic in z3fold

[Sebastian Andrzej Siewior]

On 2020-11-29 12:41:14 [+0100], Mike Galbraith wrote:
> On Sun, 2020-11-29 at 12:29 +0100, Oleksandr Natalenko wrote:
> >
> > Ummm so do compressors explode under non-rt kernel in your tests as
> > well, or it is just -rt that triggers this?
> 
> I only tested a non-rt kernel with z3fold, which worked just fine.

I tried this and it did not not explode yet. Mike, can you please
confirm?

diff --git a/mm/z3fold.c b/mm/z3fold.c
index 18feaa0bc5377..0bf70f624a4bd 100644
--- a/mm/z3fold.c
+++ b/mm/z3fold.c
@@ -642,14 +642,17 @@ static inline void add_to_unbuddied(struct z3fold_pool 
*pool,
 {
        if (zhdr->first_chunks == 0 || zhdr->last_chunks == 0 ||
                        zhdr->middle_chunks == 0) {
-               struct list_head *unbuddied = get_cpu_ptr(pool->unbuddied);
-
+               struct list_head *unbuddied;
                int freechunks = num_free_chunks(zhdr);
+
+               migrate_disable();
+               unbuddied = this_cpu_ptr(pool->unbuddied);
+
                spin_lock(&pool->lock);
                list_add(&zhdr->buddy, &unbuddied[freechunks]);
                spin_unlock(&pool->lock);
                zhdr->cpu = smp_processor_id();
-               put_cpu_ptr(pool->unbuddied);
+               migrate_enable();
        }
 }
 
@@ -887,7 +890,8 @@ static inline struct z3fold_header *__z3fold_alloc(struct 
z3fold_pool *pool,
 
 lookup:
        /* First, try to find an unbuddied z3fold page. */
-       unbuddied = get_cpu_ptr(pool->unbuddied);
+       migrate_disable();
+       unbuddied = this_cpu_ptr(pool->unbuddied);
        for_each_unbuddied_list(i, chunks) {
                struct list_head *l = &unbuddied[i];
 
@@ -905,7 +909,7 @@ static inline struct z3fold_header *__z3fold_alloc(struct 
z3fold_pool *pool,
                    !z3fold_page_trylock(zhdr)) {
                        spin_unlock(&pool->lock);
                        zhdr = NULL;
-                       put_cpu_ptr(pool->unbuddied);
+                       migrate_enable();
                        if (can_sleep)
                                cond_resched();
                        goto lookup;
@@ -919,7 +923,7 @@ static inline struct z3fold_header *__z3fold_alloc(struct 
z3fold_pool *pool,
                    test_bit(PAGE_CLAIMED, &page->private)) {
                        z3fold_page_unlock(zhdr);
                        zhdr = NULL;
-                       put_cpu_ptr(pool->unbuddied);
+                       migrate_enable();
                        if (can_sleep)
                                cond_resched();
                        goto lookup;
@@ -934,7 +938,7 @@ static inline struct z3fold_header *__z3fold_alloc(struct 
z3fold_pool *pool,
                kref_get(&zhdr->refcount);
                break;
        }
-       put_cpu_ptr(pool->unbuddied);
+       migrate_enable();
 
        if (!zhdr) {
                int cpu;
diff --git a/mm/zswap.c b/mm/zswap.c
index 78a20f7b00f2c..b24f761b9241c 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -394,7 +394,9 @@ struct zswap_comp {
        u8 *dstmem;
 };
 
-static DEFINE_PER_CPU(struct zswap_comp, zswap_comp);
+static DEFINE_PER_CPU(struct zswap_comp, zswap_comp) = {
+       .lock = INIT_LOCAL_LOCK(lock),
+};
 
 static int zswap_dstmem_prepare(unsigned int cpu)
 {

>       -Mike

Sebastian