From: Herbert Xu <herbert@gondor.apana.org.au>
To: Johannes Berg <johannes@sipsolutions.net>
Cc: linux-wireless@vger.kernel.org, netdev@vger.kernel.org,
Jouni Malinen <j@w1.fi>, Thomas Graf <tgraf@suug.ch>,
Johannes Berg <johannes.berg@intel.com>
Subject: Re: [PATCH v2] rhashtable: make walk safe from softirq context
Date: Thu, 7 Feb 2019 21:40:06 +0800 [thread overview]
Message-ID: <20190207134006.gmuooqmyc5womcaf@gondor.apana.org.au> (raw)
In-Reply-To: <20190206090721.8001-1-johannes@sipsolutions.net>
On Wed, Feb 06, 2019 at 10:07:21AM +0100, Johannes Berg wrote:
> From: Johannes Berg <johannes.berg@intel.com>
>
> When an rhashtable walk is done from softirq context, we rightfully
> get a lockdep complaint saying that we could get a softirq in the
> middle of a rehash, and thus deadlock on &ht->lock. This happened
> e.g. in mac80211 as it does a walk in softirq context.
>
> Fix this by using spin_lock_bh() wherever we use the &ht->lock.
>
> Initially, I thought it would be sufficient to do this only in the
> rehash (rhashtable_rehash_table), but I changed my mind:
> * the caller doesn't really need to disable softirqs across all
> of the rhashtable_walk_* functions, only those parts that they
> actually do within the lock need it
> * maybe more importantly, it would still lead to massive lockdep
> complaints - false positives, but hard to fix - because lockdep
> wouldn't know about different ht->lock instances, and thus one
> user of the code doing a walk w/o any locking (when it only ever
> uses process context this is fine) vs. another user like in wifi
> where we noticed this problem would still cause it to complain.
>
> Cc: stable@vger.kernel.org
> Reported-by: Jouni Malinen <j@w1.fi>
> Signed-off-by: Johannes Berg <johannes.berg@intel.com>
This interface wasn't designed for use in softirq contexts.
Could you please show me who is doing this so I can review that
to see whether it's a legitimate use of this API?
Thanks,
--
Email: Herbert Xu <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
next prev parent reply other threads:[~2019-02-07 13:40 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-06 9:07 [PATCH v2] rhashtable: make walk safe from softirq context Johannes Berg
2019-02-07 13:40 ` Herbert Xu [this message]
2019-02-07 13:50 ` Johannes Berg
2019-02-07 21:48 ` Herbert Xu
2019-02-07 21:56 ` Johannes Berg
2019-02-07 22:02 ` Herbert Xu
2019-02-12 18:43 ` David Miller
2019-02-12 19:03 ` Johannes Berg
2019-02-12 21:54 ` Bob Copeland
2019-02-13 4:35 ` Herbert Xu
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