netdev - Re: Maybe a race condition in net/rds/rdma.c?

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Date:   Fri, 6 Mar 2020 20:11:13 +0800
From:   zerons <sironhide0null@...il.com>
To:     santosh.shilimkar@...cle.com
Cc:     netdev <netdev@...r.kernel.org>,
        OFED mailing list <linux-rdma@...r.kernel.org>,
        haakon.bugge@...cle.com
Subject: Re: Maybe a race condition in net/rds/rdma.c?



On 2/28/20 02:10, santosh.shilimkar@...cle.com wrote:
> 
>>> On 18 Feb 2020, at 14:13, zerons <sironhide0null@...il.com> wrote:
>>>
>>> Hi, all
>>>
>>> In net/rds/rdma.c
>>> (https://urldefense.com/v3/__https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/net/rds/rdma.c?h=v5.5.3*n419__;Iw!!GqivPVa7Brio!OwwQCLtjDsKmhaIz0sfaOVSuC4ai5t5_FgB7yqNExGOCBtACtIGLF61NNJyqSDtIAcGoPg$ ),
>>> there may be a race condition between rds_rdma_unuse() and rds_free_mr().
>>>
> Hmmm.. I didn't see email before in my inbox. Please post questions/patches on netdev in future which is the correct mailing list.
> 
>>> It seems that this one need some specific devices to run test,
>>> unfortunately, I don't have any of these.
>>> I've already sent two emails to the maintainer for help, no response yet,
>>> (the email address may not be in use).
>>>
>>> 0) in rds_recv_incoming_exthdrs(), it calls rds_rdma_unuse() when receive an
>>> extension header with force=0, if the victim mr does not have RDS_RDMA_USE_ONCE
>>> flag set, then the mr would stay in the rbtree. Without any lock, it tries to
>>> call mr->r_trans->sync_mr().
>>>
>>> 1) in rds_free_mr(), the same mr is found, and then freed. The mr->r_refcount
>>> doesn't change while rds_mr_tree_walk().
>>>
>>> 0) back in rds_rdma_unuse(), the victim mr get used again, call
>>> mr->r_trans->sync_mr().
>>>
>>> Could this race condition actually happen?
>>>
> force=0 is an interesting scenario. Let me think about it and get back.
> Thanks for report.
> 
> Regards,
> Santosh

Thanks for your attention.

Regards,