Date: Tue, 8 May 2001 23:31:51 -0400 (EDT) From: Robert Watson <rwatson@FreeBSD.org> To: John Baldwin <jhb@FreeBSD.org> Cc: Dag-Erling Smorgrav <des@ofug.org>, freebsd-current@FreeBSD.org, freebsd-stable@frebsd.org, Kris Kennaway <kris@obsecurity.org>, Dennis Glatting <dennis.glatting@software-munitions.com>, tlambert2@mindspring.com Subject: Re: pgm to kill 4.3 via vm Message-ID: <Pine.NEB.3.96L.1010508232842.11741p-100000@fledge.watson.org> In-Reply-To: <XFMail.010508164650.jhb@FreeBSD.org>
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On Tue, 8 May 2001, John Baldwin wrote: > That's easy enough. Well, it used to be at least. You can use 'ps' to > find the address of the struct proc (first pointer in the display) and > then do 'call psignal(addr, 9)' to send SIGKILL to the process. Then > hit 'c' to continue and voila, the process dies. I think that may panic > now due to proc lock not being held (though the debugger shouldn't need > any locks in theory.) Perhaps mtx_assert() should honor db_active and > not panic if it is set. I followed everything here fine until you asserted that the debugger shouldn't need any locks. I guess I don't see why that is, at least in terms of not corrupting structures. From a practical perspective, the debugger is like any other interupt-driven preemptive code-path: if you want to modify a structure, you need to synchronize appropriately to avoid corrupting the structure. This may not be something you really want to do in a debugger, so in that sense perhaps you *shouldn't* grab a lock in the debugger, but to perform the described action safely, you *should* grab a lock so as not to corrupt fields of the proc structure (i.e., if you broke into the debugger during a non-atomic flags update). Violating system invariants is something you should be allowed to do in a debugger, but this sounded like it was a feature people were looking from to recover from unhappy behavior, not to introduce it :-). Robert N M Watson FreeBSD Core Team, TrustedBSD Project robert@fledge.watson.org NAI Labs, Safeport Network Services To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message
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