| Message ID | 20180215050224.21158-1-anand.jain@oracle.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Thu, Feb 15, 2018 at 01:02:24PM +0800, Anand Jain wrote: > btrfs_close_extra_devices() is not exactly about just closing the opened > devices, but its also about free-ing the stale devices which may have > scanned into the btrfs_fs_devices::dev_list. The way it picks devices to > be freed is by going through the btrfs_fs_devices::dev_list and its seed > devices, and finding for devices which do not have the flag > BTRFS_DEV_STATE_IN_FS_METADATA nor if it is part of the replace target. > > However, in the first place the way devices are scanned and added to the > btrfs_fs_devices::dev_list have changed for a long time now. During scan > when it finds matching fsid+uuid+devid it would add the device to > btrfs_fs_devices::dev_list. A matched device with higher generation number > overwrites the device with lower generation number during. > > Further, the stale devices containing the stale fsid are removed at the > time of the scan itself. > > So there isn't any opportunity that btrfs_close_extra_devices() can free > the stale device within the fsid which is being mounted. > > Further about the btrfs_fs_devices::latest_bdev that > the btrfs_close_extra_devices() function assigns, is already assigned by > the function __btrfs_open_devices(). > > So as this function has no effect, delete it. I think this is correct. Freeing stale devices as a side effect of mount does not seem right anyway. I'm still not able to convince myself that there's not an unexpected interaction of dev scan and dev replace, as it relies on the state bits and other locks. If you have ideas were to put some asserts or extra checks, please suggest. I found only one place where an assert could go: > - /* > - * keep the device that is marked to be the target device for the > - * dev_replace procedure > - */ > - btrfs_close_extra_devices(fs_devices, 0); > - > - if (!fs_devices->latest_bdev) { > - btrfs_err(fs_info, "failed to read devices"); > - goto fail_tree_roots; > - } ASSERT(fs_devices->latest_bdev); as latest_bdev could have been touched even by the no-op btrfs_close_extra_devices. I'll add that. Reviewed-by: David Sterba <dsterba@suse.com> -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 02/20/2018 12:53 AM, David Sterba wrote: > On Thu, Feb 15, 2018 at 01:02:24PM +0800, Anand Jain wrote: >> btrfs_close_extra_devices() is not exactly about just closing the opened >> devices, but its also about free-ing the stale devices which may have >> scanned into the btrfs_fs_devices::dev_list. The way it picks devices to >> be freed is by going through the btrfs_fs_devices::dev_list and its seed >> devices, and finding for devices which do not have the flag >> BTRFS_DEV_STATE_IN_FS_METADATA nor if it is part of the replace target. >> >> However, in the first place the way devices are scanned and added to the >> btrfs_fs_devices::dev_list have changed for a long time now. During scan >> when it finds matching fsid+uuid+devid it would add the device to >> btrfs_fs_devices::dev_list. A matched device with higher generation number >> overwrites the device with lower generation number during. >> >> Further, the stale devices containing the stale fsid are removed at the >> time of the scan itself. >> >> So there isn't any opportunity that btrfs_close_extra_devices() can free >> the stale device within the fsid which is being mounted. >> >> Further about the btrfs_fs_devices::latest_bdev that >> the btrfs_close_extra_devices() function assigns, is already assigned by >> the function __btrfs_open_devices(). >> >> So as this function has no effect, delete it. > > I think this is correct. Freeing stale devices as a side effect of mount > does not seem right anyway. I'm still not able to convince myself that > there's not an unexpected interaction of dev scan and dev replace, as > it relies on the state bits and other locks. If you have ideas were to > put some asserts or extra checks, please suggest. Thanks for comments. I took a fresh look after a long weekend. Here I found something new. Following test case [1] can simulate stale SB on the missing device which got deleted. Now if we do the fresh dev scan and mount the deleted device should not be kept in the device_list after the mount because that's stale. And as IN_FS_METADATA flag is not set on this device this function helps to clean up those devices. The dev scan free_stale can't catch this condition because we won't go deeper than the SB read. Sorry, my bad pls ignore this patch this is a very corner case or I had gone nuts when I investigated this. [1] mkfs.btrfs -fq -mraid1 -draid1 /dev/sde /dev/sdf /dev/sdg modprobe -r btrfs mount -o degraded,device=/dev/sde /dev/sdf /btrfs btrfs dev del 3 /btrfs umount /btrfs btrfs dev scan /dev/sde /dev/sdf /dev/sdg mount /dev/sde /btrfs wipefs -a /dev/sdg <-- this should work as sdg is not part of fsid mounted anymore. I am thinking to rename this function to btrfs_free_extra_devices() and add comments. Also about the fs_devices::latest_bdev we certainly assign it in __btrfs_open_devices(), but there we don't care if it picks the replacing target. And suppose if replacing_target has the highest (or equal) generation number compared to other we shall read the sys and chunk tree from it. So during the mount context we use and reconstruct using the replacing target, but at the end of mount context, we use the non-replace target as the latest_bdev. Thanks, Anand -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c index c412ad1f103b..74ee8a250b8a 100644 --- a/fs/btrfs/disk-io.c +++ b/fs/btrfs/disk-io.c @@ -2756,17 +2756,6 @@ int open_ctree(struct super_block *sb, goto fail_tree_roots; } - /* - * keep the device that is marked to be the target device for the - * dev_replace procedure - */ - btrfs_close_extra_devices(fs_devices, 0); - - if (!fs_devices->latest_bdev) { - btrfs_err(fs_info, "failed to read devices"); - goto fail_tree_roots; - } - retry_root_backup: generation = btrfs_super_generation(disk_super); @@ -2823,8 +2812,6 @@ int open_ctree(struct super_block *sb, goto fail_block_groups; } - btrfs_close_extra_devices(fs_devices, 1); - ret = btrfs_sysfs_add_fsid(fs_devices, NULL); if (ret) { btrfs_err(fs_info, "failed to init sysfs fsid interface: %d", diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c index 9bdc1cd849f2..23658876497c 100644 --- a/fs/btrfs/volumes.c +++ b/fs/btrfs/volumes.c @@ -896,69 +896,6 @@ static struct btrfs_fs_devices *clone_fs_devices(struct btrfs_fs_devices *orig) return ERR_PTR(-ENOMEM); } -void btrfs_close_extra_devices(struct btrfs_fs_devices *fs_devices, int step) -{ - struct btrfs_device *device, *next; - struct btrfs_device *latest_dev = NULL; - - mutex_lock(&uuid_mutex); -again: - /* This is the initialized path, it is safe to release the devices. */ - list_for_each_entry_safe(device, next, &fs_devices->devices, dev_list) { - if (test_bit(BTRFS_DEV_STATE_IN_FS_METADATA, - &device->dev_state)) { - if (!test_bit(BTRFS_DEV_STATE_REPLACE_TGT, - &device->dev_state) && - (!latest_dev || - device->generation > latest_dev->generation)) { - latest_dev = device; - } - continue; - } - - if (device->devid == BTRFS_DEV_REPLACE_DEVID) { - /* - * In the first step, keep the device which has - * the correct fsid and the devid that is used - * for the dev_replace procedure. - * In the second step, the dev_replace state is - * read from the device tree and it is known - * whether the procedure is really active or - * not, which means whether this device is - * used or whether it should be removed. - */ - if (step == 0 || test_bit(BTRFS_DEV_STATE_REPLACE_TGT, - &device->dev_state)) { - continue; - } - } - if (device->bdev) { - blkdev_put(device->bdev, device->mode); - device->bdev = NULL; - fs_devices->open_devices--; - } - if (test_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state)) { - list_del_init(&device->dev_alloc_list); - clear_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state); - if (!test_bit(BTRFS_DEV_STATE_REPLACE_TGT, - &device->dev_state)) - fs_devices->rw_devices--; - } - list_del_init(&device->dev_list); - fs_devices->num_devices--; - free_device(device); - } - - if (fs_devices->seed) { - fs_devices = fs_devices->seed; - goto again; - } - - fs_devices->latest_bdev = latest_dev->bdev; - - mutex_unlock(&uuid_mutex); -} - static void free_device_rcu(struct rcu_head *head) { struct btrfs_device *device; diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h index 182bfdce22b9..c8d74589426c 100644 --- a/fs/btrfs/volumes.h +++ b/fs/btrfs/volumes.h @@ -429,7 +429,6 @@ int btrfs_open_devices(struct btrfs_fs_devices *fs_devices, int btrfs_scan_one_device(const char *path, fmode_t flags, void *holder, struct btrfs_fs_devices **fs_devices_ret); int btrfs_close_devices(struct btrfs_fs_devices *fs_devices); -void btrfs_close_extra_devices(struct btrfs_fs_devices *fs_devices, int step); void btrfs_assign_next_active_device(struct btrfs_fs_info *fs_info, struct btrfs_device *device, struct btrfs_device *this_dev); int btrfs_find_device_missing_or_by_path(struct btrfs_fs_info *fs_info,
btrfs_close_extra_devices() is not exactly about just closing the opened devices, but its also about free-ing the stale devices which may have scanned into the btrfs_fs_devices::dev_list. The way it picks devices to be freed is by going through the btrfs_fs_devices::dev_list and its seed devices, and finding for devices which do not have the flag BTRFS_DEV_STATE_IN_FS_METADATA nor if it is part of the replace target. However, in the first place the way devices are scanned and added to the btrfs_fs_devices::dev_list have changed for a long time now. During scan when it finds matching fsid+uuid+devid it would add the device to btrfs_fs_devices::dev_list. A matched device with higher generation number overwrites the device with lower generation number during. Further, the stale devices containing the stale fsid are removed at the time of the scan itself. So there isn't any opportunity that btrfs_close_extra_devices() can free the stale device within the fsid which is being mounted. Further about the btrfs_fs_devices::latest_bdev that the btrfs_close_extra_devices() function assigns, is already assigned by the function __btrfs_open_devices(). So as this function has no effect, delete it. Signed-off-by: Anand Jain <anand.jain@oracle.com> --- fs/btrfs/disk-io.c | 13 ----------- fs/btrfs/volumes.c | 63 ------------------------------------------------------ fs/btrfs/volumes.h | 1 - 3 files changed, 77 deletions(-)