netdev - Re: [PATCH v2 net 2/2] net/rds: Fix MR reference counting problem

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Message-Id: <20200409.102223.182007354397877992.davem@davemloft.net>
Date:   Thu, 09 Apr 2020 10:22:23 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     ka-cheong.poon@...cle.com
Cc:     netdev@...r.kernel.org, santosh.shilimkar@...cle.com,
        rds-devel@....oracle.com, sironhide0null@...il.com
Subject: Re: [PATCH v2 net 2/2] net/rds: Fix MR reference counting problem

From: Ka-Cheong Poon <ka-cheong.poon@...cle.com>
Date: Wed,  8 Apr 2020 03:21:02 -0700

> In rds_free_mr(), it calls rds_destroy_mr(mr) directly.  But this
> defeats the purpose of reference counting and makes MR free handling
> impossible.  It means that holding a reference does not guarantee that
> it is safe to access some fields.  For example, In
> rds_cmsg_rdma_dest(), it increases the ref count, unlocks and then
> calls mr->r_trans->sync_mr().  But if rds_free_mr() (and
> rds_destroy_mr()) is called in between (there is no lock preventing
> this to happen), r_trans_private is set to NULL, causing a panic.
> Similar issue is in rds_rdma_unuse().
> 
> Reported-by: zerons <sironhide0null@...il.com>
> Signed-off-by: Ka-Cheong Poon <ka-cheong.poon@...cle.com>
> Acked-by: Santosh Shilimkar <santosh.shilimkar@...cle.com>

Applied.