drivers/zram: Don't disable preemption in zcomp_stream_get/put()

In v4.7, the driver switched to percpu compression streams, disabling
preemption via get/put_cpu_ptr(). Use a per-zcomp_strm lock here. We
also have to fix an lock order issue in zram_decompress_page() such
that zs_map_object() nests inside of zcomp_stream_put() as it does in
zram_bvec_write().

Signed-off-by: Mike Galbraith <[email protected]>
[bigeasy: get_locked_var() -> per zcomp_strm lock]
Signed-off-by: Sebastian Andrzej Siewior <[email protected]>

Author: umgwanakikbuti

drivers/block/zram/zcomp.c

@@ -118,12 +118,19 @@ ssize_t zcomp_available_show(const char *comp, char *buf)
 
 struct zcomp_strm *zcomp_stream_get(struct zcomp *comp)
 {
-	return *get_cpu_ptr(comp->stream);
+	struct zcomp_strm *zstrm;
+
+	zstrm = *this_cpu_ptr(comp->stream);
+	spin_lock(&zstrm->zcomp_lock);
+	return zstrm;
 }
 
 void zcomp_stream_put(struct zcomp *comp)
 {
-	put_cpu_ptr(comp->stream);
+	struct zcomp_strm *zstrm;
+
+	zstrm = *this_cpu_ptr(comp->stream);
+	spin_unlock(&zstrm->zcomp_lock);
 }
 
 int zcomp_compress(struct zcomp_strm *zstrm,
@@ -174,6 +181,7 @@ static int __zcomp_cpu_notifier(struct zcomp *comp,
 			pr_err("Can't allocate a compression stream\n");
 			return NOTIFY_BAD;
 		}
+		spin_lock_init(&zstrm->zcomp_lock);
 		*per_cpu_ptr(comp->stream, cpu) = zstrm;
 		break;
 	case CPU_DEAD:

drivers/block/zram/zcomp.h

@@ -14,6 +14,7 @@ struct zcomp_strm {
 	/* compression/decompression buffer */
 	void *buffer;
 	struct crypto_comp *tfm;
+	spinlock_t zcomp_lock;
 };
 
 /* dynamic per-device compression frontend */

drivers/block/zram/zram_drv.c

@@ -577,6 +577,7 @@ static int zram_decompress_page(struct zram *zram, char *mem, u32 index)
 	struct zram_meta *meta = zram->meta;
 	unsigned long handle;
 	unsigned int size;
+	struct zcomp_strm *zstrm;
 
 	zram_lock_table(&meta->table[index]);
 	handle = meta->table[index].handle;
@@ -588,16 +589,15 @@ static int zram_decompress_page(struct zram *zram, char *mem, u32 index)
 		return 0;
 	}
 
+	zstrm = zcomp_stream_get(zram->comp);
 	cmem = zs_map_object(meta->mem_pool, handle, ZS_MM_RO);
 	if (size == PAGE_SIZE) {
 		memcpy(mem, cmem, PAGE_SIZE);
 	} else {
-		struct zcomp_strm *zstrm = zcomp_stream_get(zram->comp);
-
 		ret = zcomp_decompress(zstrm, cmem, size, mem);
-		zcomp_stream_put(zram->comp);
 	}
 	zs_unmap_object(meta->mem_pool, handle);
+	zcomp_stream_put(zram->comp);
 	zram_unlock_table(&meta->table[index]);
 
 	/* Should NEVER happen. Return bio error if it does. */