[PATCH 3/9] kvm tools, qcow: Fix locking issues

Pekka Enberg
2011-07-09T13:03:01Z

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>
---
tools/kvm/disk/qcow.c | 30 +++++++++++++++++++++---------
tools/kvm/include/kvm/mutex.h | 6 ++++++
tools/kvm/include/kvm/qcow.h | 3 +++
3 files changed, 30 insertions(+), 9 deletions(-)

diff --git a/tools/kvm/disk/qcow.c b/tools/kvm/disk/qcow.c
index a1f6ef3..939bc61 100644
--- a/tools/kvm/disk/qcow.c
+++ b/tools/kvm/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;

+ mutex_unlock(&q->mutex);
+
if (pread_in_full(q->fd, dst, length, clust_start + clust_offset) < 0)
- goto out_error;
+ 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);
diff --git a/tools/kvm/include/kvm/mutex.h b/tools/kvm/include/kvm/mutex.h
index bd765c4..3286cea 100644
--- a/tools/kvm/include/kvm/mutex.h
+++ b/tools/kvm/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)
diff --git a/tools/kvm/include/kvm/qcow.h b/tools/kvm/include/kvm/qcow.h
index 12247e0..d44c64a 100644
--- a/tools/kvm/include/kvm/qcow.h
+++ b/tools/kvm/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;
--
1.7.0.4