On Mon, May 28, 2018 at 10:43:29PM +0800, Anand Jain wrote: > btrfs_free_extra_devids() is called only in the mount context which > traverses through the fs_devices::devices and frees the orphan devices > devices in the given %fs_devices if any. As the search for the orphan > device is limited to fs_devices::devices so we don't need the global > uuid_mutex. > > There can't be any mount-point based ioctl threads in this context as > the mount thread is not yet returned. But there can be the btrfs-control > based scan ioctls thread which calls device_list_add(). > > Here in the mount thread the fs_devices::opened is incremented way before > btrfs_free_extra_devids() is called and in the scan context the fs_devices > which are already opened neither be freed or alloc-able at > device_list_add(). > > But lets say you change the device-path and call the scan again, then scan > would update the new device path and this operation could race against the > btrfs_free_extra_devids() thread, which might be in the process of > free-ing the same device. So synchronize it by using the > device_list_mutex. > > This scenario is a very corner case, and practically the scan and mount > are anyway serialized by the usage so unless the race is instrumented its > very difficult to achieve. > > Signed-off-by: Anand Jain <anand.j...@oracle.com> > --- > (I didn't see this email in the mailing list, so trying again). > v3->v4: As we traverse through the seed device, fs_device gets updated with > the child seed fs_devices, so make sure we use the same fs_devices > pointer for the mutex_unlock as used for the mutex_lock.
Well, now that I see the change, shouldn't we always hold the device_list_mutex of the fs_devices that's being processed? Ie. each time it's switched, the previous is unlocked and new one locked. -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
