Hi, On Thu, Mar 20, 2014 at 02:30:04PM -0500, Felipe Balbi wrote: > From: Huang Shijie <b32955@xxxxxxxxxxxxx> > > 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@xxxxxxxxxxxxx> > Signed-off-by: Felipe Balbi <balbi@xxxxxx> patch came without a subject, Peter already sent it anyway, so Greg can ignore this one. -- balbi
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