On Tue, 14 Jun 2016 18:55:26 +0800, Anand Jain wrote:
> Further to the previous commit
> bc178622d40d87e75abc131007342429c9b03351
> btrfs: use rcu_barrier() to wait for bdev puts at unmount
>
> Since free_device() spinoff __free_device() the rcu_barrier() for
> call_rcu(&device->rcu, free_device);
> didn't help.
>
> This patch reverts changes by
> bc178622d40d87e75abc131007342429c9b03351
> and implement a method to wait on the __free_device() by using
> a new bdev_closing member in struct btrfs_device.
>
> Signed-off-by: Anand Jain <anand.j...@oracle.com>
> [rework: bc178622d40d87e75abc131007342429c9b03351]
> ---
> fs/btrfs/volumes.c | 44 ++++++++++++++++++++++++++++++++++++++------
> fs/btrfs/volumes.h | 1 +
> 2 files changed, 39 insertions(+), 6 deletions(-)
>
> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
> index a4e8d48acd4b..404ce1daebb1 100644
> --- a/fs/btrfs/volumes.c
> +++ b/fs/btrfs/volumes.c
> @@ -27,6 +27,7 @@
> #include <linux/raid/pq.h>
> #include <linux/semaphore.h>
> #include <linux/uuid.h>
> +#include <linux/delay.h>
> #include <asm/div64.h>
> #include "ctree.h"
> #include "extent_map.h"
> @@ -254,6 +255,17 @@ static struct btrfs_device *__alloc_device(void)
> return dev;
> }
>
> +static int is_device_closing(struct list_head *head)
> +{
> + struct btrfs_device *dev;
> +
> + list_for_each_entry(dev, head, dev_list) {
> + if (dev->bdev_closing)
> + return 1;
> + }
> + return 0;
> +}
> +
> static noinline struct btrfs_device *__find_device(struct list_head *head,
> u64 devid, u8 *uuid)
> {
> @@ -832,12 +844,22 @@ again:
> static void __free_device(struct work_struct *work)
> {
> struct btrfs_device *device;
> + struct btrfs_device *new_device_addr;
>
> device = container_of(work, struct btrfs_device, rcu_work);
>
> if (device->bdev)
> blkdev_put(device->bdev, device->mode);
>
> + /*
> + * If we are coming here from btrfs_close_one_device()
> + * then it allocates a new device structure for the same
> + * devid, so find device again with the devid
> + */
> + new_device_addr = __find_device(&device->fs_devices->devices,
> + device->devid, NULL);
> +
> + new_device_addr->bdev_closing = 0;
> rcu_string_free(device->name);
> kfree(device);
> }
> @@ -884,6 +906,12 @@ static void btrfs_close_one_device(struct btrfs_device
> *device)
> list_replace_rcu(&device->dev_list, &new_device->dev_list);
> new_device->fs_devices = device->fs_devices;
>
> + /*
> + * So to wait for kworkers to finish all blkdev_puts,
> + * so device is really free when umount is done.
> + */
> + new_device->bdev_closing = 1;
> +
> call_rcu(&device->rcu, free_device);
> }
>
> @@ -912,6 +940,7 @@ int btrfs_close_devices(struct btrfs_fs_devices
> *fs_devices)
> {
> struct btrfs_fs_devices *seed_devices = NULL;
> int ret;
> + int retry_cnt = 5;
>
> mutex_lock(&uuid_mutex);
> ret = __btrfs_close_devices(fs_devices);
> @@ -927,12 +956,15 @@ int btrfs_close_devices(struct btrfs_fs_devices
> *fs_devices)
> __btrfs_close_devices(fs_devices);
> free_fs_devices(fs_devices);
> }
> - /*
> - * Wait for rcu kworkers under __btrfs_close_devices
> - * to finish all blkdev_puts so device is really
> - * free when umount is done.
> - */
> - rcu_barrier();
> +
> + while (is_device_closing(&fs_devices->devices) &&
> + --retry_cnt) {
> + mdelay(1000); //1 sec
> + }
> +
> + if (!(retry_cnt > 0))
> + printk(KERN_WARNING "BTRFS: %pU bdev_put didn't complete,
> giving up\n",
> + fs_devices->fsid);
> return ret;
> }
>
> diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
> index 0ac90f8d85bd..945e49f5e17d 100644
> --- a/fs/btrfs/volumes.h
> +++ b/fs/btrfs/volumes.h
> @@ -150,6 +150,7 @@ struct btrfs_device {
> /* Counter to record the change of device stats */
> atomic_t dev_stats_ccnt;
> atomic_t dev_stat_values[BTRFS_DEV_STAT_VALUES_MAX];
> + int bdev_closing;
> };
>
> /*
> --
> 2.7.0
I gave this a try and somehow it seems to make unmounting worse:
it now always takes ~5s (max retry time) and I see the warning every
time. Without the patch unmounting a single volume (disk) is much
faster (1-2s), without problems.
Any ideas?
cheers,
Holger
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