linux-kernel - Re: [PATCH] bluetooth: 6lowpan: fix delay work init in add_peer

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Message-Id: <6B40174C-6834-4C3D-BF41-92119E78E353@holtmann.org>
Date:   Fri, 31 Mar 2017 12:10:44 +0200
From:   Marcel Holtmann <marcel@...tmann.org>
To:     Michael Scott <michael.scott@...aro.org>
Cc:     "Gustavo F. Padovan" <gustavo@...ovan.org>,
        Johan Hedberg <johan.hedberg@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jukka Rissanen <jukka.rissanen@...ux.intel.com>,
        linux-bluetooth@...r.kernel.org, linux-wpan@...r.kernel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] bluetooth: 6lowpan: fix delay work init in
 add_peer_chan()

Hi Michael,

> When adding 6lowpan devices very rapidly we sometimes see a crash:
> [23122.306615] CPU: 2 PID: 0 Comm: swapper/2 Not tainted 4.9.0-43-arm64 #1 Debian 4.9.9.linaro.43-1
> [23122.315400] Hardware name: HiKey Development Board (DT)
> [23122.320623] task: ffff800075443080 task.stack: ffff800075484000
> [23122.326551] PC is at expire_timers+0x70/0x150
> [23122.330907] LR is at run_timer_softirq+0xa0/0x1a0
> [23122.335616] pc : [<ffff000008142dd8>] lr : [<ffff000008142f58>] pstate: 600001c5
> 
> This was due to add_peer_chan() unconditionally initializing the
> lowpan_btle_dev->notify_peers delayed work structure, even if the
> lowpan_btle_dev passed into add_peer_chan() had previously been
> initialized.
> 
> Normally, this would go unnoticed as the delayed work timer is set for
> 100 msec, however when calling add_peer_chan() faster than 100 msec it
> clears out a previously queued delay work causing the crash above.
> 
> To fix this, let add_peer_chan() know when a new lowpan_btle_dev is passed
> in so that it only performs the delay work initialization when needed.
> 
> Signed-off-by: Michael Scott <michael.scott@...aro.org>
> ---
> net/bluetooth/6lowpan.c | 10 +++++++---
> 1 file changed, 7 insertions(+), 3 deletions(-)

patch has been applied to bluetooth-next tree.

Regards

Marcel