If mkfs on device mapper thin pool fails, it will show pool status
as returned by dmsetup for enahnced error reporting.
Signed-off-by: Alakesh Haloi <alakeshh@amazon.com>
Before the change, the error on the caller-side (e.g. ctr) was
something like
> unpack: failed to prepare extraction snapshot "...": exit status 5:
> unknown
which was too cryptic.
Signed-off-by: Kazuyoshi Kato <katokazu@amazon.com>
The issue beblow happens several times beforing the root
cause found:
1. A `fdisk -l` process has being hung up for a long time;
2. A image layer snapshot device is visiable to dmsetup, which
should *not* happen because it should be deactivated after
`Commit()`;
The backtrace of `fdisk` is always the same over time:
```bash
[<ffffffff810bbc6a>] io_schedule+0x2a/0x80
[<ffffffff81295a3f>] do_blockdev_direct_IO+0x1e9f/0x2f10
[<ffffffff81296aea>] __blockdev_direct_IO+0x3a/0x40
[<ffffffff81290e43>] blkdev_direct_IO+0x43/0x50
[<ffffffff811b8a14>] generic_file_read_iter+0x374/0x960
[<ffffffff81291ad5>] blkdev_read_iter+0x35/0x40
[<ffffffff8125229b>] new_sync_read+0xfb/0x240
[<ffffffff81252406>] __vfs_read+0x26/0x40
[<ffffffff81252b96>] vfs_read+0x96/0x130
[<ffffffff812540e5>] SyS_read+0x55/0xc0
[<ffffffff81003c04>] do_syscall_64+0x74/0x180
```
The root cause is, in Commit(), there's a race window between
`SuspendDevice()` and `DeactivateDevice()`, which may cause the
IOs of a process or command like `fdisk` on the "suspended" device
hang up forever. It has twofold:
1. The IOs suspends on the devices;
2. The device is in `Suspended` state, because it's deactivated with
`deferred` flag and without `force` flag;
So they cannot make progress.
One reproducer is:
1. enlarge the race window by putting sleep seconds there;
2. run `while true; do sudo fdisk -l; sleep 0.5; done` on one terminal;
3. and pull image on another terminal;
Fixes it by:
1. Resume the devices again after flushing IO by suspend;
2. Remove device without `deferred` flag;
Fix: #4234
Signed-off-by: Eric Ren <renzhen@linux.alibaba.com>
Snapshots GC takes use of pruneBranch() function to remove snapshots,
but GC will stop if snapshotter.Remove() returns error and the error
number is not ErrFailedPrecondition. This results in thousands of
dm snapshots not deleted if one snapshot is not deleted, due to
errors like "contains a filesystem in use".
So return ErrFailedPrecondition error number in Remove() function where
appropriate, and let GC process go on collecting other snapshots.
Fix: #3923
Signed-off-by: Eryu Guan <eguan@linux.alibaba.com>
Signed-off-by: Eric Ren <renzhen.rz@linux.alibaba.com>
1. reason to deactivate committed snapshot
The thin device will not be used for IO after committed,
and further thin snapshotting is OK using an inactive thin
device as origin. The benefits to deactivate are:
- device is not unneccesary visible avoiding any unexpected IO;
- save useless kernel data structs for maintaining active dm.
Quote from kernel doc (Documentation/device-mapper/provisioning.txt):
"
ii) Using an internal snapshot.
Once created, the user doesn't have to worry about any connection
between the origin and the snapshot. Indeed the snapshot is no
different from any other thinly-provisioned device and can be
snapshotted itself via the same method. It's perfectly legal to
have only one of them active, and there's no ordering requirement on
activating or removing them both. (This differs from conventional
device-mapper snapshots.)
"
2. an thinpool metadata bug is naturally removed
An problem happens when failed to suspend/resume origin thin device
when creating snapshot:
"failed to create snapshot device from parent vg0-mythinpool-snap-3"
error="failed to save initial metadata for snapshot "vg0-mythinpool-snap-19":
object already exists"
This issue occurs because when failed to create snapshot, the
snapshotter.store can be rollbacked, but the thin pool metadata
boltdb failed to rollback in PoolDevice.CreateSnapshotDevice(),
therefore metadata becomes inconsistent: the snapshotID is not
taken in snapshotter.store, but saved in pool metadata boltdb.
The cause is, in PoolDevice.CreateSnapshotDevice(), the defer calls
are invoked on "first-in-last-out" order. When the error happens
on the "resume device" defer call, the metadata is saved and
snapshot is created, which has no chance to be rollbacked.
Signed-off-by: Eric Ren <renzhen@linux.alibaba.com>
