linux-kernel - Re: [PATCH 4/5] target: Fix multi-session dynamic se_node

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Date:   Wed, 08 Feb 2017 08:14:57 -0800
From:   "Nicholas A. Bellinger" <nab@...ux-iscsi.org>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     target-devel <target-devel@...r.kernel.org>,
        linux-scsi <linux-scsi@...r.kernel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Rob Millner <rlm@...erainc.com>
Subject: Re: [PATCH 4/5] target: Fix multi-session dynamic se_node_acl
 double free OOPs

On Tue, 2017-02-07 at 19:46 -0800, Nicholas A. Bellinger wrote:
> On Tue, 2017-02-07 at 15:12 -0800, Christoph Hellwig wrote:
> > And the real patch after compile fixing it is here of course:
> > 
> 
> Getting rid of the extra se_node_acl->acl_free_comp seems to make sense
> here..
> 
> The only potential issue is if returning from configfs syscall
> rmdir /sys/kernel/config/target/$FABRIC/$WWN/$TPGT/acls/$INITIATOR/
> before se_node_acl memory is released has implications when the
> underlying ../$WWN/$TPGT/ is removed immediately after.
> 
> In any event, I'll verify this patch with the original test case and use
> it instead if everything looks OK.

Ok, I remember why se_node_acl->acl_free_comp is needed now..

The issue is when se_node_acl is being explicitly removed from configfs
while se_sessions associated with se_node_acl are still active.

The se_node_acl->acl_group configfs_group_operations->drop_item()
callback must block until all associated se_sessions have done their
target_put_nacl() and completed se_node_acl->acl_free_comp, otherwise
there is nothing preventing parent config_groups of se_node_acl from
being removed while the se_sessions are still active.

That said, dropping the unnecessary list_del_init() usage, but otherwise
keeping the patch as-is.