linux-kernel - Re: Race condition in Kernel

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Date:   Thu, 25 Mar 2021 09:46:13 +0800
From:   Ming Lei <ming.lei@...hat.com>
To:     Gulam Mohamed <gulam.mohamed@...cle.com>
Cc:     "hch@...radead.org" <hch@...radead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        Junxiao Bi <junxiao.bi@...cle.com>,
        Martin Petersen <martin.petersen@...cle.com>,
        "axboe@...nel.dk" <axboe@...nel.dk>
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?

-- 
Ming