kvm tools, qcow: Fix locking issues

The virtio_blk_do_io() function can enter the QCOW code through
disk_image__{read,write,flush}() from multiple threads because it uses a thread
pool for I/O requests. Thus, use locking to make the QCOW2 code thread-safe.

Cc: Asias He <asias.hejun@gmail.com>
Cc: Cyrill Gorcunov <gorcunov@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Prasad Joshi <prasadjoshi124@gmail.com>
Cc: Sasha Levin <levinsasha928@gmail.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>

disk/qcow.c

@@ -2,6 +2,7 @@
 
 #include "kvm/disk-image.h"
 #include "kvm/read-write.h"
+#include "kvm/mutex.h"
 #include "kvm/util.h"
 
 #include <sys/types.h>
@@ -232,16 +233,17 @@ static ssize_t qcow_read_cluster(struct qcow *q, u64 offset, void *dst, u32 dst_
 
 	l1_idx = get_l1_index(q, offset);
 	if (l1_idx >= table->table_size)
-		goto out_error;
+		return -1;
 
 	clust_offset = get_cluster_offset(q, offset);
 	if (clust_offset >= cluster_size)
-		goto out_error;
+		return -1;
 
 	length = cluster_size - clust_offset;
 	if (length > dst_len)
 		length = dst_len;
 
+	mutex_lock(&q->mutex);
 	l2_table_offset = table->l1_table[l1_idx] & ~header->oflag_mask;
 	if (!l2_table_offset)
 		goto zero_cluster;
@@ -261,19 +263,22 @@ static ssize_t qcow_read_cluster(struct qcow *q, u64 offset, void *dst, u32 dst_
 	if (!clust_start)
 		goto zero_cluster;
 
-	if (pread_in_full(q->fd, dst, length, clust_start + clust_offset) < 0)
-		goto out_error;
+	mutex_unlock(&q->mutex);
+
+	if (pread_in_full(q->fd, dst, length, clust_start + clust_offset) < 0)
+		return -1;
 
-out:
 	return length;
 
 zero_cluster:
+	mutex_unlock(&q->mutex);
 	memset(dst, 0, length);
-	goto out;
+	return length;
 
 out_error:
+	mutex_unlock(&q->mutex);
 	length = -1;
-	goto out;
+	return -1;
 }
 
 static ssize_t qcow_read_sector(struct disk_image *disk, u64 sector, void *dst, u32 dst_len)
@@ -379,20 +384,22 @@ static ssize_t qcow_write_cluster(struct qcow *q, u64 offset, void *buf, u32 src
 
 	l1t_idx		= get_l1_index(q, offset);
 	if (l1t_idx >= table->table_size)
-		goto error;
+		return -1;
 
 	l2t_idx		= get_l2_index(q, offset);
 	if (l2t_idx >= l2t_sz)
-		goto error;
+		return -1;
 
 	clust_off	= get_cluster_offset(q, offset);
 	if (clust_off >= clust_sz)
-		goto error;
+		return -1;
 
 	len		= clust_sz - clust_off;
 	if (len > src_len)
 		len = src_len;
 
+	mutex_lock(&q->mutex);
+
 	l2t_off		= table->l1_table[l1t_idx] & ~header->oflag_mask;
 	if (l2t_off) {
 		/* read and cache l2 table */
@@ -466,11 +473,14 @@ static ssize_t qcow_write_cluster(struct qcow *q, u64 offset, void *buf, u32 src
 		l2t->table[l2t_idx] = clust_start;
 	}
 
+	mutex_unlock(&q->mutex);
+
 	return len;
 
 free_cache:
 	free(l2t);
 error:
+	mutex_unlock(&q->mutex);
 	return -1;
 }
 
@@ -611,6 +621,7 @@ static struct disk_image *qcow2_probe(int fd, bool readonly)
 	if (!q)
 		goto error;
 
+	mutex_init(&q->mutex);
 	q->fd = fd;
 	q->root = RB_ROOT;
 	INIT_LIST_HEAD(&q->lru_list);
@@ -710,6 +721,7 @@ static struct disk_image *qcow1_probe(int fd, bool readonly)
 	if (!q)
 		goto error;
 
+	mutex_init(&q->mutex);
 	q->fd = fd;
 	q->root = RB_ROOT;
 	INIT_LIST_HEAD(&q->lru_list);

include/kvm/mutex.h

@@ -12,6 +12,12 @@
 
 #define DEFINE_MUTEX(mutex) pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER
 
+static inline void mutex_init(pthread_mutex_t *mutex)
+{
+	if (pthread_mutex_init(mutex, NULL) != 0)
+		die("unexpected pthread_mutex_init() failure!");
+}
+
 static inline void mutex_lock(pthread_mutex_t *mutex)
 {
 	if (pthread_mutex_lock(mutex) != 0)

include/kvm/qcow.h

@@ -1,6 +1,8 @@
 #ifndef KVM__QCOW_H
 #define KVM__QCOW_H
 
+#include "kvm/mutex.h"
+
 #include <linux/types.h>
 #include <stdbool.h>
 #include <linux/rbtree.h>
@@ -34,6 +36,7 @@ struct qcow_table {
 };
 
 struct qcow {
+	pthread_mutex_t		mutex;
 	void			*header;
 	struct qcow_table	table;
 	int			fd;