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Subject[PATCH 2/5] Btrfs: fix the race between reading and updating devices
On btrfs_congested_fn and __unplug_io_fn paths, we should hold
device_list_mutex to avoid remove/add device path to
update fs_devices->devices

On __btrfs_close_devices and btrfs_prepare_sprout paths, the devices in
fs_devices->devices or fs_devices->devices is updated, so we should hold
the mutex to avoid the reader side to reach them

Signed-off-by: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
---
fs/btrfs/disk-io.c | 4 ++++
fs/btrfs/volumes.c | 7 +++++++
2 files changed, 11 insertions(+), 0 deletions(-)

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index ef6865c..5a70096 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -1412,6 +1412,7 @@ static int btrfs_congested_fn(void *congested_data, int bdi_bits)
struct btrfs_device *device;
struct backing_dev_info *bdi;

+ mutex_lock(&info->fs_devices->device_list_mutex);
list_for_each_entry(device, &info->fs_devices->devices, dev_list) {
if (!device->bdev)
continue;
@@ -1421,6 +1422,7 @@ static int btrfs_congested_fn(void *congested_data, int bdi_bits)
break;
}
}
+ mutex_unlock(&info->fs_devices->device_list_mutex);
return ret;
}

@@ -1434,6 +1436,7 @@ static void __unplug_io_fn(struct backing_dev_info *bdi, struct page *page)
struct btrfs_fs_info *info;

info = (struct btrfs_fs_info *)bdi->unplug_io_data;
+ mutex_lock(&info->fs_devices->device_list_mutex);
list_for_each_entry(device, &info->fs_devices->devices, dev_list) {
if (!device->bdev)
continue;
@@ -1442,6 +1445,7 @@ static void __unplug_io_fn(struct backing_dev_info *bdi, struct page *page)
if (bdi->unplug_io_fn)
bdi->unplug_io_fn(bdi, page);
}
+ mutex_unlock(&info->fs_devices->device_list_mutex);
}

static void btrfs_unplug_io_fn(struct backing_dev_info *bdi, struct page *page)
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 69fc902..a672249 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -515,6 +515,7 @@ static int __btrfs_close_devices(struct btrfs_fs_devices *fs_devices)
if (--fs_devices->opened > 0)
return 0;

+ mutex_lock(&fs_devices->device_list_mutex);
list_for_each_entry(device, &fs_devices->devices, dev_list) {
if (device->bdev) {
blkdev_put(device->bdev, device->mode);
@@ -529,6 +530,8 @@ static int __btrfs_close_devices(struct btrfs_fs_devices *fs_devices)
device->writeable = 0;
device->in_fs_metadata = 0;
}
+ mutex_unlock(&fs_devices->device_list_mutex);
+
WARN_ON(fs_devices->open_devices);
WARN_ON(fs_devices->rw_devices);
fs_devices->opened = 0;
@@ -1449,7 +1452,11 @@ static int btrfs_prepare_sprout(struct btrfs_trans_handle *trans,
INIT_LIST_HEAD(&seed_devices->devices);
INIT_LIST_HEAD(&seed_devices->alloc_list);
mutex_init(&seed_devices->device_list_mutex);
+
+ mutex_lock(&root->fs_info->fs_devices->device_list_mutex);
list_splice_init(&fs_devices->devices, &seed_devices->devices);
+ mutex_unlock(&root->fs_info->fs_devices->device_list_mutex);
+
list_splice_init(&fs_devices->alloc_list, &seed_devices->alloc_list);
list_for_each_entry(device, &seed_devices->devices, dev_list) {
device->fs_devices = seed_devices;
--
1.7.4.4


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