linux-kernel - Re: [PATCH] configfs: Fix race between create_link and configfs

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Message-ID: <1496991903.28997.74.camel@haakon3.risingtidesystems.com>
Date:   Fri, 09 Jun 2017 00:05:03 -0700
From:   "Nicholas A. Bellinger" <nab@...ux-iscsi.org>
To:     "Bryant G. Ly" <bryantly@...ux.vnet.ibm.com>
Cc:     Christoph Hellwig <hch@....de>,
        target-devel <target-devel@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        linux-scsi <linux-scsi@...r.kernel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Joel Becker <jlbec@...lplan.org>
Subject: Re: [PATCH] configfs: Fix race between create_link and
 configfs_rmdir

On Thu, 2017-06-08 at 07:34 -0500, Bryant G. Ly wrote:
> > Thanks Nic,
> >
> > applied to the configfs-for-next tree.  I'm not entirely sure if we
> > should bother adding this to 4.12 or if it hits rarely enough?
> >
> It hits for us pretty often when we have a GPFS setup with 10 hosts and 1k+ vms.
> 
> That is how we discovered the bug in the first place.
> 

Using a DATERA workload with 1K unique multi-tenant backend devices and
1K unique iscsi-target IQNs per node, I've never tripped across this
particular bug..

However, our userspace built atop rtslib is enforcing tenant shutdown of
individual rmdir(2) of /sys/kernel/config/target/$FABRIC/$WWN/$TPGT/,
before rmdir(2) of /sys/kernel/config/target/core/$HBA/$DEV/ occurs.

Based on Bryant's original backtrace with targetcli, it looks like the
Novalink user-space is not enforcing this requirement across user-space
processes doing fabric port symlink and backend device shutdown.

That said it probably doesn't need a special v4.12-rc PULL, but based on
Bryant's feedback it certainly does deserve a stable CC'.