Hi Ming,
Thanks for taking a look into this. Can you please see my inline comments
in below mail?
Regards,
Gulam Mohamed.
-----Original Message-----
From: Ming Lei <[email protected]>
Sent: Thursday, March 25, 2021 7:16 AM
To: Gulam Mohamed <[email protected]>
Cc: [email protected]; [email protected];
[email protected]; Junxiao Bi <[email protected]>; Martin
Petersen <[email protected]>; [email protected]
Subject: Re: Race condition in Kernel
On Wed, Mar 24, 2021 at 12:37:03PM +0000, Gulam Mohamed wrote:
> Hi All,
>
> We are facing a stale link (of the device) issue during the iscsi-logout
> process if we use parted command just before the iscsi logout. Here are the
> details:
>
> As part of iscsi logout, the partitions and the disk will be removed. The
> parted command, used to list the partitions, will open the disk in RW mode
> which results in systemd-udevd re-reading the partitions. This will trigger
> the rescan partitions which will also delete and re-add the partitions. So,
> both iscsi logout processing and the parted (through systemd-udevd) will be
> involved in add/delete of partitions. In our case, the following sequence of
> operations happened (the iscsi device is /dev/sdb with partition sdb1):
>
> 1. sdb1 was removed by PARTED
> 2. kworker, as part of iscsi logout, couldn't remove sdb1 as it was
> already removed by PARTED
> 3. sdb1 was added by parted
After kworker is started for logout, I guess all IOs are supposed to be failed
at that time, so just wondering why 'sdb1' is still added by
parted(systemd-udev)?
ioctl(BLKRRPART) needs to read partition table for adding back partitions, if
IOs are failed by iscsi logout, I guess the issue can be avoided too?
[GULAM]: Yes, the ioctl(BLKRRPART) reads the partition table for adding back
the partitions. I kept a printk in the code just after the partition table is
read. Noticed that the partition table was read before the iscsi-logout kworker
started the logout processing.
Following are the logs for your reference:
Apr 1 09:23:27 gms-iscsi-initiator-2 kernel: ORA:: Calling
sysfs_delete_link() for dev: sdb3 command: systemd-udevd <== sdb3
Removed by PARTED
Apr 1 09:23:27 gms-iscsi-initiator-2 kernel: ORA:: rescan_partitions() Read
Complete to the disk: sdb command: systemd-udevd <== Reading sdb completed,
before iscsi-logout worker started
Apr 1 09:23:27 gms-iscsi-initiator-2 kernel: ORA:: Calling sysfs_delete_link()
for dev: 3:0:0:0 command: kworker/u16:3
Apr 1 09:23:27 gms-iscsi-initiator-2 kernel: sdb: sdb1 sdb2 sdb3
Apr 1 09:23:27 gms-iscsi-initiator-2 kernel: ORA:: device: 'sdb3': device_add
command: systemd-udevd <== sdb3 Added by PARTED
Apr 1 09:23:27 gms-iscsi-initiator-2 kernel: ORA:: Calling sysfs_delete_link()
for dev: 8:16 command: kworker/u16:3
Apr 1 09:23:27 gms-iscsi-initiator-2 kernel: ORA:: Calling sysfs_delete_link()
for dev: sdb command: kworker/u16:3 <== sdb Removed by iscsi
Apr 1 09:23:27 gms-iscsi-initiator-2 kernel: scsi 3:0:0:0: alua: Detached
--
Ming
