On 06/19/2016 12:34 AM, Holger Hoffstätte wrote:
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.jain@xxxxxxxxxx> [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; }; /* -- 2.7.0I 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.
Thanks Holger, for testing. It depends on long the blkdev_put() will take, originally unmount thread didn't wait for it to complete, so it was faster, but had other problem as explained. Thanks, Anand
Any ideas?
cheers, Holger
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