linux-kernel - Re: [PATCH] nvme: fix lockdep warning in nvme_mpath_clear_current

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20180514124230.GA654@infradead.org>
Date:   Mon, 14 May 2018 05:42:30 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Johannes Thumshirn <jthumshirn@...e.de>
Cc:     Keith Busch <keith.busch@...el.com>,
        Sagi Grimberg <sagi@...mberg.me>,
        Linux Kernel Mailinglist <linux-kernel@...r.kernel.org>,
        Linux NVMe Mailinglist <linux-nvme@...ts.infradead.org>,
        Hannes Reinecke <hare@...e.de>, Christoph Hellwig <hch@....de>,
        paulmck@...ux.vnet.ibm.com
Subject: Re: [PATCH] nvme: fix lockdep warning in
 nvme_mpath_clear_current_path

>  extern unsigned int nvme_io_timeout;
>  #define NVME_IO_TIMEOUT	(nvme_io_timeout * HZ)
> @@ -454,7 +455,9 @@ static inline void nvme_mpath_clear_current_path(struct nvme_ns *ns)
>  {
>  	struct nvme_ns_head *head = ns->head;
>  
> -	if (head && ns == srcu_dereference(head->current_path, &head->srcu))
> +	if (head &&
> +	    ns == rcu_dereference_protected(head->current_path,
> +				lockdep_is_held(&ns->ctrl->subsys->lock)))
>  		rcu_assign_pointer(head->current_path, NULL);
>  }
>  struct nvme_ns *nvme_find_path(struct nvme_ns_head *head);

We don't really dereference it at all in fact, but just check the
pointers for equality.  I wonder if there is a better way to do this,
as my ANA patches add a caller without the lock (and withou SRU
protection either now that I think of it) - for a pure pointer compare
we really should not need any sort of protection.