Date: Thu, 1 Jan 2004 11:48:24 -0500 (EST) From: Daniel Eischen <eischen@vigrid.com> To: David Xu <davidxu@freebsd.org> Cc: arch@freebsd.org Subject: Re: sigaltstack with threads Message-ID: <Pine.GSO.4.10.10401011138130.18629-100000@pcnet5.pcnet.com> In-Reply-To: <3FF43B93.5060209@freebsd.org>
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On Thu, 1 Jan 2004, David Xu wrote: > Doug Rabson wrote: > > I think that if its supported at all in threaded programs, it must be > > per-thread state otherwise you can't prevent two different threads > > colliding on the same signal stack. I can't quite see how this maps to > > KSE/KSEG since I only have the most hazy model of that stuff in my head > > right now. > > > > Anyway, I've worked around things by not setting SA_ONSTACK for the > > handlers that I want to run on the thread stack. > > > > > I have worked out a patch to support per-thread sigaltstack() state, > in most cases, it is just a literally replacement. > > http://people.freebsd.org/~davidxu/kse/kern_sigaltstack.diffs Looks good, but I have a question. You removed the proc lock in kern_sig.c:osigstack() and kern_sig.c:kern_sigaltstack(). What prevents a signal from being sent to the current thread while it is mucking with the altsigstack? Is it possible for an interrupt to swap out the current thread and have a signal installed for it sometime later before it can complete sigaltstack()? Or do signals only get installed on the way out of the kernel? -- Dan Eischen
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