Date: Sat, 26 Jun 2004 21:57:13 -0400 (EDT) From: Robert Watson <rwatson@freebsd.org> To: Bruce Evans <bde@zeta.org.au> Cc: current@freebsd.org Subject: Re: SMP turbulence: "kernel trap 12 with interrupts disabled" Message-ID: <Pine.NEB.3.96L.1040626215516.58671O-100000@fledge.watson.org> In-Reply-To: <20040627111227.V1642@gamplex.bde.org>
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On Sun, 27 Jun 2004, Bruce Evans wrote: > > I ran into this also -- I got a panic when I hit a key on the serial > > console, as that caused the sio intr to preempt the ACPI idle loop and > > resulted in unhappiness somehow. I found that when I disabled the tunable > > that turns off HTT, it worked fine. Likewise, if I used 4BSD it was fine. > > It's unclear to me what the cause is. > > This looks like phk's roto-tilling of com->hotchar to > com->tp->t_hotchar. Hitting a key on a serial console that has not been > opened from userland is the most deterministic way to demonstrate the > brokenness of this change in practice. com->tp is NULL until first > open, and the null pointer access is especially easy to reach using a > serial console since it is in the interrupt handler and interrupts are > enabled before open on serial consoles to support trapping to the > debugger on them. You probably need the options that give this early > enabling to see the bug. They are: Ah, indeed, and with the ULE+HTT+machdep.hlt_logical_cpus bug, it would hangs very early, opening up the window for the race. Robert N M Watson FreeBSD Core Team, TrustedBSD Projects robert@fledge.watson.org Principal Research Scientist, McAfee Research > > %%% > #if defined(DDB) && (defined(BREAK_TO_DEBUGGER) || \ > defined(ALT_BREAK_TO_DEBUGGER)) > %%% > > Bruce >
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