svn commit: r212076 - head/lib/libthr/thread
Kostik Belousov
kostikbel at gmail.com
Thu Sep 2 09:26:38 UTC 2010
On Thu, Sep 02, 2010 at 05:03:13PM +0000, David Xu wrote:
> Kostik Belousov wrote:
> >On Thu, Sep 02, 2010 at 04:34:58PM +0000, David Xu wrote:
> >>Kostik Belousov wrote:
> >>>On Wed, Sep 01, 2010 at 02:18:33AM +0000, David Xu wrote:
> >>>>Author: davidxu
> >>>>Date: Wed Sep 1 02:18:33 2010
> >>>>New Revision: 212076
> >>>>URL: http://svn.freebsd.org/changeset/base/212076
> >>>>
> >>>>Log:
> >>>> Add signal handler wrapper, the reason to add it becauses there are
> >>>> some cases we want to improve:
> >>>> 1) if a thread signal got a signal while in cancellation point,
> >>>> it is possible the TDP_WAKEUP may be eaten by signal handler
> >>>> if the handler called some interruptibly system calls.
> >>>> 2) In signal handler, we want to disable cancellation.
> >>>> 3) When thread holding some low level locks, it is better to
> >>>> disable signal, those code need not to worry reentrancy,
> >>>> sigprocmask system call is avoided because it is a bit expensive.
> >>>> The signal handler wrapper works in this way:
> >>>> 1) libthr installs its signal handler if user code invokes sigaction
> >>>> to install its handler, the user handler is recorded in internal
> >>>> array.
> >>>> 2) when a signal is delivered, libthr's signal handler is invoke,
> >>>> libthr checks if thread holds some low level lock or is in
> >>>> critical
> >>>> region, if it is true, the signal is buffered, and all signals are
> >>>> masked, once the thread leaves critical region, correct signal
> >>>> mask is restored and buffered signal is processed.
> >>>> 3) before user signal handler is invoked, cancellation is temporarily
> >>>> disabled, after user signal handler is returned, cancellation
> >>>> state
> >>>> is restored, and pending cancellation is rescheduled.
> >>>>+static void
> >>>>+thr_sighandler(int sig, siginfo_t *info, void *_ucp)
> >>>>+{
> >>>>+ if ((actp->sa_flags & SA_SIGINFO) != 0)
> >>>>+ (*(sigfunc))(sig, info, ucp);
> >>>>+ else {
> >>>>+ ((ohandler)(*sigfunc))(
> >>>>+ sig, info->si_code, (struct sigcontext *)ucp,
> >>>>+ info->si_addr, (__sighandler_t *)sigfunc);
> >>>>+ }
> >>>I do not think this is very important, but freebsd old-style signal
> >>>handler fourth argument is usually the faulted %eip value. This is
> >>>most likely irrelevant for any source that is linked with libthr.so
> >>>new enough to contain this change.
> >>Isn't the si_addr in siginfo a fault address ? I remembered I saved
> >>the fault address in ksiginfo_t which is converted to userland
> >>siginfo, and fault address should be there. what's wrong here ?
> >>
> >Oops, sorry, I miscalculated the position of the arguments :(.
>
> Sorry, I think I also misunderstood you too. :(
> I think kernel still has some compatible problems. I just skimmed
> it again, and I found a problem.
>
> In RELENG_4, I found sys/i386/i386/machdep.c has following code in
> sendsig():
>
>
> sf.sf_signum = sig;
> sf.sf_ucontext = (register_t)&sfp->sf_uc;
> if (SIGISMEMBER(p->p_sigacts->ps_siginfo, sig)) {
> /* Signal handler installed with SA_SIGINFO. */
> sf.sf_siginfo = (register_t)&sfp->sf_si;
> sf.sf_ahu.sf_action = (__siginfohandler_t *)catcher;
>
> /* fill siginfo structure */
> sf.sf_si.si_signo = sig;
> sf.sf_si.si_code = code;
> sf.sf_si.si_addr = (void*)regs->tf_err;
> }
> else {
> /* Old FreeBSD-style arguments. */
> sf.sf_siginfo = code;
> sf.sf_addr = regs->tf_err; <-------
> sf.sf_ahu.sf_handler = catcher;
> }
>
> the sf.sf_addr is assigned by tf_err here.
>
> In later branch ( I don't know which ), it seems it uses ksi.ksi_addr,
>
> /* Old FreeBSD-style arguments. */
> sf.sf_arg2 = ksi->ksi_code;
> sf.sf_addr = (register_t)ksi->ksi_addr;
> sf.sf_ahu.sf_handler = catcher;
>
>
>
> the tf_err may not be equal to ksi_addr! This may need to be fixed.
>
The change was introduced by
r151316 | davidxu | 2005-10-14
/* Old FreeBSD-style arguments. */
- sf.sf_siginfo = code;
- sf.sf_addr = regs->tf_err;
+ sf.sf_siginfo = ksi->ksi_code;
+ sf.sf_addr = (register_t)ksi->ksi_addr;
sf.sf_ahu.sf_handler = catcher;
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