Message-ID: <20140423151548.GA10025@t440s.P-661HNU-F1>
Date:	Wed, 23 Apr 2014 18:15:48 +0300
From:	Johan Hedberg <johan.hedberg@...il.com>
To:	Andreas Bießmann <andreas@...ssmann.de>
Cc:	linux-kernel@...r.kernel.org,
	Marcel Holtmann <marcel@...tmann.org>,
	Gustavo Padovan <gustavo@...ovan.org>,
	linux-bluetooth@...r.kernel.org
Subject: Re: [PATCH] bluetooth:hci_ldisc: add tasklet for deferred TX handling

Hi Andreas,

On Wed, Apr 16, 2014, Andreas Bießmann wrote:
> This patch fixes a recursive locking scenario when using BCSP connection via
> 8250 driver. The 8250 driver may tty_wakeup() in interrupt context which
> results in hci_uart_tx_wakeup(). This in turn will call uart_write() in the
> very same context and therefore will spin_lock() the same lock within the
> same context.
> 
> Here is the call stack:
> 
> ---8<---
> =============================================
> [ INFO: possible recursive locking detected ]
> 3.4.87-gf1a3cc3 #3 Tainted: G           O
> ---------------------------------------------
> swapper/0 is trying to acquire lock:
>  (&port_lock_key){-.-...}, at: [<c023e21c>] uart_write+0x60/0xfc
> 
> but task is already holding lock:
>  (&port_lock_key){-.-...}, at: [<c0242830>] serial8250_handle_irq+0x24/0x88
> 
> other info that might help us debug this:
>  Possible unsafe locking scenario:
> 
>        CPU0
>        ----
>   lock(&port_lock_key);
>   lock(&port_lock_key);
> 
>  *** DEADLOCK ***
> 
>  May be due to missing lock nesting notation
> 
> 2 locks held by swapper/0:
>  #0:  (&(&i->lock)->rlock){-.-...}, at: [<c0240f44>] serial8250_interrupt+0x2c/0xc0
>  #1:  (&port_lock_key){-.-...}, at: [<c0242830>] serial8250_handle_irq+0x24/0x88
> 
> stack backtrace:
> [<c0014234>] (unwind_backtrace+0x0/0xec) from [<c0398448>] (dump_stack+0x20/0x24)
> [<c0398448>] (dump_stack+0x20/0x24) from [<c006eebc>] (print_deadlock_bug+0xb4/0xe4)
> [<c006eebc>] (print_deadlock_bug+0xb4/0xe4) from [<c006f04c>] (check_deadlock.isra.20+0x160/0x18c)
> [<c006f04c>] (check_deadlock.isra.20+0x160/0x18c) from [<c0070890>] (validate_chain.isra.24+0x4a4/0x4f0)
> [<c0070890>] (validate_chain.isra.24+0x4a4/0x4f0) from [<c00715a0>] (__lock_acquire+0x670/0x740)
> [<c00715a0>] (__lock_acquire+0x670/0x740) from [<c0071cb0>] (lock_acquire+0x138/0x15c)
> [<c0071cb0>] (lock_acquire+0x138/0x15c) from [<c03a5904>] (_raw_spin_lock_irqsave+0x54/0x68)
> [<c03a5904>] (_raw_spin_lock_irqsave+0x54/0x68) from [<c023e21c>] (uart_write+0x60/0xfc)
> [<c023e21c>] (uart_write+0x60/0xfc) from [<bf0716d8>] (hci_uart_tx_wakeup+0x9c/0x160 [hci_uart])
> [<bf0716d8>] (hci_uart_tx_wakeup+0x9c/0x160 [hci_uart]) from [<bf0717f4>] (hci_uart_tty_wakeup+0x58/0x5c [hci_uart])
> [<bf0717f4>] (hci_uart_tty_wakeup+0x58/0x5c [hci_uart]) from [<c02246ec>] (tty_wakeup+0x48/0x68)
> [<c02246ec>] (tty_wakeup+0x48/0x68) from [<c023efb0>] (uart_write_wakeup+0x2c/0x30)
> [<c023efb0>] (uart_write_wakeup+0x2c/0x30) from [<c0241d0c>] (serial8250_tx_chars+0xf0/0x140)
> [<c0241d0c>] (serial8250_tx_chars+0xf0/0x140) from [<c0242878>] (serial8250_handle_irq+0x6c/0x88)
> [<c0242878>] (serial8250_handle_irq+0x6c/0x88) from [<c02428c4>] (serial8250_default_handle_irq+0x30/0x34)
> [<c02428c4>] (serial8250_default_handle_irq+0x30/0x34) from [<c0240f5c>] (serial8250_interrupt+0x44/0xc0)
> [<c0240f5c>] (serial8250_interrupt+0x44/0xc0) from [<c0087c70>] (handle_irq_event_percpu+0xc4/0x2cc)
> [<c0087c70>] (handle_irq_event_percpu+0xc4/0x2cc) from [<c0087ec4>] (handle_irq_event+0x4c/0x6c)
> [<c0087ec4>] (handle_irq_event+0x4c/0x6c) from [<c008a368>] (handle_edge_irq+0x114/0x14c)
> [<c008a368>] (handle_edge_irq+0x114/0x14c) from [<c0087528>] (generic_handle_irq+0x40/0x54)
> [<c0087528>] (generic_handle_irq+0x40/0x54) from [<c01f1900>] (gpio_irq_handler+0x168/0x1ac)
> [<c01f1900>] (gpio_irq_handler+0x168/0x1ac) from [<c0087528>] (generic_handle_irq+0x40/0x54)
> [<c0087528>] (generic_handle_irq+0x40/0x54) from [<c000ed7c>] (handle_IRQ+0x70/0x94)
> [<c000ed7c>] (handle_IRQ+0x70/0x94) from [<c000877c>] (omap3_intc_handle_irq+0x64/0x78)
> [<c000877c>] (omap3_intc_handle_irq+0x64/0x78) from [<c000df44>] (__irq_svc+0x44/0x78)
> --->8---
> 
> Signed-off-by: Andreas Bießmann <andreas@...ssmann.de>
> Cc: Marcel Holtmann <marcel@...tmann.org>
> Cc: Gustavo Padovan <gustavo@...ovan.org>
> Cc: Johan Hedberg <johan.hedberg@...il.com>
> Cc: linux-bluetooth@...r.kernel.org
> ---
> 
> It seems at least one other guy had the very same problem with another uart
> (mpc52xx): http://www.spinics.net/lists/linux-rt-users/msg09246.html
> 
> I wonder, if my approach is right. It is runtime tested with 3.4.87 on our
> board and work around the mentioned recursive locking. But I do not know, if
> it should be fixed in another way.
> If it is right, I'd work some more on it to get the fix mainline.
> 
>  drivers/bluetooth/hci_ldisc.c |   49 ++++++++++++++++++++++++++++++++++++-----
>  drivers/bluetooth/hci_uart.h  |    2 ++
>  2 files changed, 45 insertions(+), 6 deletions(-)

This seems to be tackling the same problem as the following patch from
Felipe Balbi (of which a new revision was sent earlier today):

	Subject: [PATCH 02/13] bluetooth: hci_ldisc: fix deadlock condition

Johan
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