[PATCH] staging: zram: Avoid lockdep warning

[Jerome Marchand]

zram triggers a lockdep warning. The cause of it is the call to
zram_init_device() from zram_make_request(). The memory allocation in
zram_init_device() could start a memory reclaim which in turn could
cause swapout and (as it appears to lockdep) a call to
zram_make_request(). However this is a false positive: an
unititialized device can't be used as swap.
A solution is to split init_lock in two lock. One mutex that protects
init, reset and size setting and a rw_semaphore that protects requests
and reset. Thus init and request would be protected by different locks
and lockdep will be happy.

Signed-off-by: Jerome Marchand <jmarchan@xxxxxxxxxx>
---
 drivers/staging/zram/zram_drv.c   |   41 +++++++++++++++++++-----------------
 drivers/staging/zram/zram_drv.h   |   16 ++++++++++---
 drivers/staging/zram/zram_sysfs.c |   20 +++++++++---------
 3 files changed, 44 insertions(+), 33 deletions(-)

diff --git a/drivers/staging/zram/zram_drv.c b/drivers/staging/zram/zram_drv.c
index fb4a7c9..b3bc3c4 100644
--- a/drivers/staging/zram/zram_drv.c
+++ b/drivers/staging/zram/zram_drv.c
@@ -470,11 +470,11 @@ static void zram_make_request(struct request_queue *queue, struct bio *bio)
 {
 	struct zram *zram = queue->queuedata;
 
-	if (unlikely(!zram->init_done) && zram_init_device(zram))
+	if (unlikely(!is_initialized(zram)) && zram_init_device(zram))
 		goto error;
 
-	down_read(&zram->init_lock);
-	if (unlikely(!zram->init_done))
+	down_read(&zram->req_lock);
+	if (unlikely(!is_initialized(zram)))
 		goto error_unlock;
 
 	if (!valid_io_request(zram, bio)) {
@@ -483,12 +483,12 @@ static void zram_make_request(struct request_queue *queue, struct bio *bio)
 	}
 
 	__zram_make_request(zram, bio, bio_data_dir(bio));
-	up_read(&zram->init_lock);
+	up_read(&zram->req_lock);
 
 	return;
 
 error_unlock:
-	up_read(&zram->init_lock);
+	up_read(&zram->req_lock);
 error:
 	bio_io_error(bio);
 }
@@ -497,7 +497,7 @@ void __zram_reset_device(struct zram *zram)
 {
 	size_t index;
 
-	zram->init_done = 0;
+	atomic_set(&zram->init_done, 0);
 
 	/* Free various per-device buffers */
 	kfree(zram->compress_workmem);
@@ -529,9 +529,12 @@ void __zram_reset_device(struct zram *zram)
 
 void zram_reset_device(struct zram *zram)
 {
-	down_write(&zram->init_lock);
-	__zram_reset_device(zram);
-	up_write(&zram->init_lock);
+	mutex_lock(&zram->init_lock);
+	down_write(&zram->req_lock);
+	if (is_initialized(zram))
+		__zram_reset_device(zram);
+	up_write(&zram->req_lock);
+	mutex_unlock(&zram->init_lock);
 }
 
 int zram_init_device(struct zram *zram)
@@ -539,10 +542,10 @@ int zram_init_device(struct zram *zram)
 	int ret;
 	size_t num_pages;
 
-	down_write(&zram->init_lock);
+	mutex_lock(&zram->init_lock);
 
-	if (zram->init_done) {
-		up_write(&zram->init_lock);
+	if (is_initialized(zram)) {
+		mutex_unlock(&zram->init_lock);
 		return 0;
 	}
 
@@ -583,8 +586,8 @@ int zram_init_device(struct zram *zram)
 		goto fail;
 	}
 
-	zram->init_done = 1;
-	up_write(&zram->init_lock);
+	atomic_set(&zram->init_done, 1);
+	mutex_unlock(&zram->init_lock);
 
 	pr_debug("Initialization done!\n");
 	return 0;
@@ -594,7 +597,7 @@ fail_no_table:
 	zram->disksize = 0;
 fail:
 	__zram_reset_device(zram);
-	up_write(&zram->init_lock);
+	mutex_unlock(&zram->init_lock);
 	pr_err("Initialization failed: err=%d\n", ret);
 	return ret;
 }
@@ -619,7 +622,8 @@ static int create_device(struct zram *zram, int device_id)
 	int ret = 0;
 
 	init_rwsem(&zram->lock);
-	init_rwsem(&zram->init_lock);
+	mutex_init(&zram->init_lock);
+	init_rwsem(&zram->req_lock);
 	spin_lock_init(&zram->stat64_lock);
 
 	zram->queue = blk_alloc_queue(GFP_KERNEL);
@@ -672,7 +676,7 @@ static int create_device(struct zram *zram, int device_id)
 		goto out;
 	}
 
-	zram->init_done = 0;
+	atomic_set(&zram->init_done, 0);
 
 out:
 	return ret;
@@ -755,8 +759,7 @@ static void __exit zram_exit(void)
 		zram = &zram_devices[i];
 
 		destroy_device(zram);
-		if (zram->init_done)
-			zram_reset_device(zram);
+		zram_reset_device(zram);
 	}
 
 	unregister_blkdev(zram_major, "zram");
diff --git a/drivers/staging/zram/zram_drv.h b/drivers/staging/zram/zram_drv.h
index df2eec4..f6bcead 100644
--- a/drivers/staging/zram/zram_drv.h
+++ b/drivers/staging/zram/zram_drv.h
@@ -96,9 +96,12 @@ struct zram {
 				   * against concurrent read and writes */
 	struct request_queue *queue;
 	struct gendisk *disk;
-	int init_done;
-	/* Prevent concurrent execution of device init, reset and R/W request */
-	struct rw_semaphore init_lock;
+	atomic_t init_done;
+	/* Prevent concurrent execution of device init, reset and
+	 * disksize_store */
+	struct mutex init_lock;
+	/* Prevent concurent execution device reset and R/W requests */
+	struct rw_semaphore req_lock;
 	/*
 	 * This is the limit on amount of *uncompressed* worth of data
 	 * we can store in a disk.
@@ -108,6 +111,11 @@ struct zram {
 	struct zram_stats stats;
 };
 
+static inline int is_initialized(struct zram *zram)
+{
+	return atomic_read(&zram->init_done);
+}
+
 extern struct zram *zram_devices;
 unsigned int zram_get_num_devices(void);
 #ifdef CONFIG_SYSFS
@@ -115,6 +123,6 @@ extern struct attribute_group zram_disk_attr_group;
 #endif
 
 extern int zram_init_device(struct zram *zram);
-extern void __zram_reset_device(struct zram *zram);
+extern void zram_reset_device(struct zram *zram);
 
 #endif
diff --git a/drivers/staging/zram/zram_sysfs.c b/drivers/staging/zram/zram_sysfs.c
index de1eacf..b300881 100644
--- a/drivers/staging/zram/zram_sysfs.c
+++ b/drivers/staging/zram/zram_sysfs.c
@@ -62,16 +62,19 @@ static ssize_t disksize_store(struct device *dev,
 	if (!disksize)
 		return -EINVAL;
 
-	down_write(&zram->init_lock);
-	if (zram->init_done) {
-		up_write(&zram->init_lock);
+	mutex_lock(&zram->init_lock);
+	down_write(&zram->req_lock);
+	if (is_initialized(zram)) {
+		up_write(&zram->req_lock);
+		mutex_unlock(&zram->init_lock);
 		pr_info("Cannot change disksize for initialized device\n");
 		return -EBUSY;
 	}
 
 	zram->disksize = PAGE_ALIGN(disksize);
 	set_capacity(zram->disk, zram->disksize >> SECTOR_SHIFT);
-	up_write(&zram->init_lock);
+	up_write(&zram->req_lock);
+	mutex_unlock(&zram->init_lock);
 
 	return len;
 }
@@ -81,7 +84,7 @@ static ssize_t initstate_show(struct device *dev,
 {
 	struct zram *zram = dev_to_zram(dev);
 
-	return sprintf(buf, "%u\n", zram->init_done);
+	return sprintf(buf, "%u\n", atomic_read(&zram->init_done));
 }
 
 static ssize_t reset_store(struct device *dev,
@@ -110,10 +113,7 @@ static ssize_t reset_store(struct device *dev,
 	if (bdev)
 		fsync_bdev(bdev);
 
-	down_write(&zram->init_lock);
-	if (zram->init_done)
-		__zram_reset_device(zram);
-	up_write(&zram->init_lock);
+	zram_reset_device(zram);
 
 	return len;
 }
@@ -186,7 +186,7 @@ static ssize_t mem_used_total_show(struct device *dev,
 	u64 val = 0;
 	struct zram *zram = dev_to_zram(dev);
 
-	if (zram->init_done)
+	if (is_initialized(zram))
 		val = zs_get_total_size_bytes(zram->mem_pool);
 
 	return sprintf(buf, "%llu\n", val);
-- 
1.7.7.6
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