Re: [PATCH] bluetooth:hci_ldisc: add tasklet for deferred TX handling

[Andreas BieÃmann]

Hi Johan,

Am 2014-04-23 17:15, schrieb Johan Hedberg:
> On Wed, Apr 16, 2014, Andreas BieÃmann 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 BieÃmann <andreas@xxxxxxxxxxxx>
> > Cc: Marcel Holtmann <marcel@xxxxxxxxxxxx>
> > Cc: Gustavo Padovan <gustavo@xxxxxxxxxxx>
> > Cc: Johan Hedberg <johan.hedberg@xxxxxxxxx>
> > Cc: linux-bluetooth@xxxxxxxxxxxxxxx
> > ---
> >
> > 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

seems so, thanks for the pointer!

Best regards

Andreas BieÃmann
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