From: Johannes Berg <johannes@sipsolutions.net>
To: Stanislaw Gruszka <sgruszka@redhat.com>
Cc: linux-wireless@vger.kernel.org
Subject: Re: [PATCH 2/2] mac80211: protect skb_queue_len(&ps->bc_buf) by lock
Date: Wed, 19 Feb 2014 15:51:43 +0100 [thread overview]
Message-ID: <1392821503.4733.26.camel@jlt4.sipsolutions.net> (raw)
In-Reply-To: <20140219133546.GE1851@redhat.com>
On Wed, 2014-02-19 at 14:35 +0100, Stanislaw Gruszka wrote:
> > It ultimately makes no difference at all, it just makes this code more
> > difficult to read and understand.
>
> It make difference when queue length value is modified on different CPU
> and read on different CPU. Without lock you can 'see' old length value
> on CPU that run ieee80211_tx_h_multicast_ps_buf() for undefined
> period of time (ok maybe not undefined on x86), and current oldest
> frame can be not necessarily dropped.
I don't see how that can be true, since the modifications of the queue
length are under spinlock with the implied memory barriers.
johannes
next prev parent reply other threads:[~2014-02-19 14:51 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-02-19 12:28 [PATCH 1/2] mac80211: fix calling ieee80211_free_txskb with NULL skb Stanislaw Gruszka
2014-02-19 12:28 ` [PATCH 2/2] mac80211: protect skb_queue_len(&ps->bc_buf) by lock Stanislaw Gruszka
2014-02-19 13:14 ` Johannes Berg
2014-02-19 13:35 ` Stanislaw Gruszka
2014-02-19 14:51 ` Johannes Berg [this message]
2014-02-19 15:09 ` Stanislaw Gruszka
2014-02-19 16:36 ` Johannes Berg
2014-02-20 7:56 ` Stanislaw Gruszka
2014-02-20 7:59 ` Johannes Berg
2014-02-20 8:17 ` Stanislaw Gruszka
2014-02-19 12:33 ` [PATCH 1/2] mac80211: fix calling ieee80211_free_txskb with NULL skb Johannes Berg
2014-02-19 12:39 ` Grumbach, Emmanuel
2014-02-19 12:46 ` Grumbach, Emmanuel
2014-02-19 13:21 ` Stanislaw Gruszka
2014-02-19 14:48 ` Stanislaw Gruszka
2014-02-19 14:50 ` Johannes Berg
2014-02-19 15:00 ` Stanislaw Gruszka
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