On Wed, Sep 22, 2010 at 11:46:27AM -0700, Linus Torvalds wrote: > On Wed, Sep 22, 2010 at 11:32 AM, Al Viro <viro@xxxxxxxxxxxxxxxxxx> wrote: > > > > That has unpleasant results - for starters, delivery of SIGSEGV upon > > failure to set sigframe up is delayed unpredictably; we will take it > > only when we trap again. > > I think this whole argument is a total red herring. > > It's a bug in next_signal() if we allow this to happen. We need to > enqueue those synchronous signals first, and NO AMOUNT OF SIGNAL > QUEUEING will ever change that. > > The fact is, even if you queue up all the signals at once, you need to > queue up the synchronous ones first. Otherwise their instruction > pointer information etc will simply be bogus. It's that simple. Your > argument about queuing up one, two, or more signals is bogus, for the > simple reason that it doesn't matter: whether you queue or not is > irrelevant, since the "innermost" one in the queue always has to be > the SIGSEGV. > > Whether we queue other signals on top of that (and they get executed > first, since it's a stack) doesn't matter. That's a timing issue, and > the program acts as if those asynchronous signals happened before the > trap. But that's fine. All that matters is that the actual synchronous > signal has the register contents of the time of the synchronous trap, > ie it gets enqueued first. > > It's why we have that "if (x & SYNCHRONOUS_MASK)" in next_signal(). > It's not pretty, it's not perfect, but it's required. Um, no. You've *already* called get_signal_to_deliver(). There had been no SIGSEGV in sight. You happily went on to set a sigframe for e.g. SIGHUP, but ran out of stack. At that point you get force_sigsegv() from handle_signal(). _NOW_ you have a pending SIGSEGV; whether you'll be able to handle it (e.g. if your SIGSEGV handler is set to run on altstack) or not, you won't get to it until you call get_signal_to_deliver() again. Which requires do_signal() to run. Sure, it will be the first one to be picked, but we need to try and pick _something_ to get it. -- To unsubscribe from this list: send the line "unsubscribe sparclinux" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
