linux-kernel - Re: [PATCH] Bluetooth: avoid recursive locking in hci_send_to

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Message-Id: <19282780-42CE-43C9-928E-73F4135D359A@holtmann.org>
Date:   Mon, 30 Oct 2017 09:05:02 +0100
From:   Marcel Holtmann <marcel@...tmann.org>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     Mart van de Wege <mvdwege@...il.com>,
        Johan Hedberg <johan.hedberg@...el.com>,
        "Gustavo F. Padovan" <gustavo@...ovan.org>,
        "open list:BLUETOOTH DRIVERS" <linux-bluetooth@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-rt-users@...r.kernel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH] Bluetooth: avoid recursive locking in
 hci_send_to_channel()

Hi Sebastian,

> Mart reported a deadlock in -RT in the call path:
>  hci_send_monitor_ctrl_event() -> hci_send_to_channel()
> 
> because both functions acquire the same read lock hci_sk_list.lock. This
> is also a mainline issue because the qrwlock implementation is writer
> fair (the traditional rwlock implementation is reader biased).
> 
> To avoid the deadlock there is now __hci_send_to_channel() which expects
> the readlock to be held.
> 
> Cc: Marcel Holtmann <marcel@...tmann.org>
> Cc: Johan Hedberg <johan.hedberg@...el.com>
> Fixes: 38ceaa00d02d ("Bluetooth: Add support for sending MGMT commands and events to monitor")
> Reported-by: Mart van de Wege <mvdwege@...il.com>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> ---
> net/bluetooth/hci_sock.c | 17 +++++++++++------
> 1 file changed, 11 insertions(+), 6 deletions(-)

patch has been applied to bluetooth-next tree.

Regards

Marcel