On Thu, Mar 20, 2014 at 12:16:22PM -0500, Felipe Balbi wrote: > On Thu, Mar 20, 2014 at 04:42:16PM +0000, Alan Cox wrote: > > On Thu, 2014-03-20 at 11:34 -0500, Felipe Balbi wrote: > > > Hi, > > > > > > when 8250 driver calls uart_write_wakeup(), the tty port lock is already > > > taken. hci_ldisc.c's implementation of ->write_wakeup() calls > > > tty->ops->write() to actually send the characters, but that call will > > > try to acquire the same port lock again. > > > > > > Looking at other line disciplines that looks like a bug in hci_ldisc.c. > > > Am I correct to assume that ->write_wakeup() is supposed to *just* > > > wakeup the bottom half so we handle ->write() in another context ? > > > > > > Is it legal to call tty->ops->write() from within ->write_wakeup() ? > > > > It isn't because you might send all the bytes and go > > > > write > > write_wakeup > > write > > write wakeup > > ... > > > > and recurse then we need updates to Documentation: Documentation/serial/tty.txt:: | Driver Side Interfaces: | | receive_buf() - Hand buffers of bytes from the driver to the ldisc | for processing. Semantics currently rather | mysterious 8( | | write_wakeup() - May be called at any point between open and close. | The TTY_DO_WRITE_WAKEUP flag indicates if a call | is needed but always races versus calls. Thus the | ldisc must be careful about setting order and to | handle unexpected calls. Must not sleep. | | The driver is forbidden from calling this directly | from the ->write call from the ldisc as the ldisc | is permitted to call the driver write method from | this function. In such a situation defer it. documentation says ldisc is allowed to call ->write() from ->write_wakeup(). huh ? -- balbi
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