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879eb9c3f9
In the uart_handle_cts_change(), uart_write_wakeup() is called after we call @uart_port->ops->start_tx(). The Documentation/serial/driver tells us: ----------------------------------------------- start_tx(port) Start transmitting characters. Locking: port->lock taken. Interrupts: locally disabled. ----------------------------------------------- So when the uart_write_wakeup() is called, the port->lock is taken by the upper. See the following callstack: |_ uart_write_wakeup |_ tty_wakeup |_ ld->ops->write_wakeup With the port->lock held, we call the @write_wakeup. Some implemetation of the @write_wakeup does not notice that the port->lock is held, and it still tries to send data with uart_write() which will try to grab the prot->lock. A dead lock occurs, see the following log caught in the Bluetooth by uart: -------------------------------------------------------------------- BUG: spinlock lockup suspected on CPU#0, swapper/0/0 lock: 0xdc3f4410, .magic: dead4ead, .owner: swapper/0/0, .owner_cpu: 0 CPU: 0 PID: 0 Comm: swapper/0 Tainted: G W 3.10.17-16839-ge4a1bef #1320 [<80014cbc>] (unwind_backtrace+0x0/0x138) from [<8001251c>] (show_stack+0x10/0x14) [<8001251c>] (show_stack+0x10/0x14) from [<802816ac>] (do_raw_spin_lock+0x108/0x184) [<802816ac>] (do_raw_spin_lock+0x108/0x184) from [<806a22b0>] (_raw_spin_lock_irqsave+0x54/0x60) [<806a22b0>] (_raw_spin_lock_irqsave+0x54/0x60) from [<802f5754>] (uart_write+0x38/0xe0) [<802f5754>] (uart_write+0x38/0xe0) from [<80455270>] (hci_uart_tx_wakeup+0xa4/0x168) [<80455270>] (hci_uart_tx_wakeup+0xa4/0x168) from [<802dab18>] (tty_wakeup+0x50/0x5c) [<802dab18>] (tty_wakeup+0x50/0x5c) from [<802f81a4>] (imx_rtsint+0x50/0x80) [<802f81a4>] (imx_rtsint+0x50/0x80) from [<802f88f4>] (imx_int+0x158/0x17c) [<802f88f4>] (imx_int+0x158/0x17c) from [<8007abe0>] (handle_irq_event_percpu+0x50/0x194) [<8007abe0>] (handle_irq_event_percpu+0x50/0x194) from [<8007ad60>] (handle_irq_event+0x3c/0x5c) -------------------------------------------------------------------- This patch adds more limits to the @write_wakeup, the one who wants to implemet the @write_wakeup should follow the limits which avoid the deadlock. Signed-off-by: Huang Shijie <b32955@freescale.com> Signed-off-by: Felipe Balbi <balbi@ti.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
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