On Tuesday 17 June 2014 11:03:50 David Laight wrote: > From: Peter Hurley > ... > > > I don't understand the second half of the changelog, it doesn't seem > > > to fit here: there deadlock that we are trying to avoid here happens > > > when the *same* tty needs the lock to complete the function that > > > sends the pending data. I don't think we do still do that any more, > > > but it doesn't seem related to the tty lock being system-wide or not. > > > > The tty lock is not used in the i/o path; it's purpose is to > > mutually exclude state changes in open(), close() and hangup(). > > > > The commit that added this [1] comments that _other_ ttys may wait > > for this tty to complete, and comments in the code note that this > > function should be removed when the system-wide tty mutex was removed > > (which happened with the commit noted in the changelog). > > What happens if another process tries to do a non-blocking open > while you are sleeping in close waiting for output to drain? > > Hopefully this returns before that data has drained. Before the patch, I believe tty_reopen() would return -EIO because the TTY_CLOSING flag is set. After the patch, tty_open() blocks on tty_lock() before calling tty_reopen(). AFAICT, this is independent of O_NONBLOCK. Arnd -- To unsubscribe from this list: send the line "unsubscribe linux-serial" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
