On Thu, Nov 26, 2020 at 08:07:32PM +0800, Qinglang Miao wrote: > 在 2020/11/26 17:42, Benjamin Block 写道: > > On Thu, Nov 26, 2020 at 09:13:53AM +0100, Cornelia Huck wrote: > > > On Thu, 26 Nov 2020 09:27:41 +0800 > > > Qinglang Miao <miaoqingl...@huawei.com> wrote: > > > > 在 2020/11/26 1:06, Benjamin Block 写道: > > > > > On Fri, Nov 20, 2020 at 03:48:54PM +0800, Qinglang Miao wrote: .... > > Let's go by example. If we assume the reference count of `unit->dev` is > > R, and the function starts with R = 1 (otherwise the deivce would've > > been freed already), we get: > > > > int zfcp_unit_remove(struct zfcp_port *port, u64 fcp_lun) > > { > > struct zfcp_unit *unit; > > struct scsi_device *sdev; > > write_lock_irq(&port->unit_list_lock); > > // unit->dev (R = 1) > > unit = _zfcp_unit_find(port, fcp_lun); > > // get_device(&unit->dev) > > // unit->dev (R = 2) > > if (unit) > > list_del(&unit->list); > > write_unlock_irq(&port->unit_list_lock); > > if (!unit) > > return -EINVAL; > > sdev = zfcp_unit_sdev(unit); > > if (sdev) { > > scsi_remove_device(sdev); > > scsi_device_put(sdev); > > } > > // unit->dev (R = 2) > > put_device(&unit->dev); > > // unit->dev (R = 1) > > device_unregister(&unit->dev); > > // unit->dev (R = 0) > > return 0; > > } > > > > If we now apply this patch, we'd end up with R = 1 after > > `device_unregister()`, and the device would not be properly removed. > > > > If you still think that's wrong, then you'll need to better explain why. > > > Hi Banjamin and Cornelia, > > Your replies make me reliaze that I've been holding a mistake understanding > of put_device() as well as reference count. > > Thanks for you two's patient explanation !! > > BTW, should I send a v2 on these two patches to move the position of > put_device()?
Feel free to do so. I think having the `put_device()` call after `device_unregister()` in both `zfcp_unit_remove()` and `zfcp_sysfs_port_remove_store()` is more natural, because it ought to be the last time we touch the object in both functions. -- Best Regards, Benjamin Block / Linux on IBM Z Kernel Development / IBM Systems IBM Deutschland Research & Development GmbH / https://www.ibm.com/privacy Vorsitz. AufsR.: Gregor Pillen / Geschäftsführung: Dirk Wittkopp Sitz der Gesellschaft: Böblingen / Registergericht: AmtsG Stuttgart, HRB 243294