Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Sat, 27 Oct 2001 12:23:30 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Sat, 27 Oct 2001 12:23:23 -0400 Received: from harpo.it.uu.se ([130.238.12.34]:28126 "EHLO harpo.it.uu.se") by vger.kernel.org with ESMTP id ; Sat, 27 Oct 2001 12:23:04 -0400 Date: Sat, 27 Oct 2001 18:23:33 +0200 (MET DST) From: Mikael Pettersson Message-Id: <200110271623.SAA04333@harpo.it.uu.se> To: alan@lxorguk.ukuu.org.uk, torvalds@transmeta.com Subject: [PATCH] fix 2.4 SMP kernel hang on UP P4 Cc: linux-kernel@vger.kernel.org Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Linus & Alan, A 2.4 kernel built with SMP or UP_APIC support may hang during boot if run on a UP P4 machine. The patch below fixes this, please apply. The events that lead to the hang are: 1. The BIOS boots the OS with the local APIC enabled. cpu_has_apic is true. 2. init_apic_mappings() calls detect_init_APIC(). 3. detect_init_APIC() doesn't know about the P4, so it returns failure. 4. init_apic_mappings() maps the local APIC to a dummy page. 5. Much later, APIC_init_uniprocessor() sees that cpu_has_apic is true, so it calls setup_APIC_clocks(). 6. setup_APIC_clocks() calls calibrate_APIC_clock(). 7. Since the local APIC was mapped to a dummy page, calibrate_APIC_clock() doesn't actually touch the HW. It detects and returns a 0 MHz bus clock. 8. setup_APIC_clocks() calls setup_APIC_timer() with the 0 MHz bus clock. 9. setup_APIC_timer() spins in a loop, waiting to APIC_TMCCT to decrement. But APIC_TMCCT is in the dummy page, so it doesn't change and the loop never terminates. At this point, you'll see something like: Using local APIC timer interrupts. calibrating APIC timer ... ..... CPU clock speed is 1707.5365 MHz. ..... host bus clock speed is 0.0000 MHz. cpu: 0, clocks: 0, slice: 0 // hangs The fix simply ensures that detect_init_APIC() doesn't return failure when running on a P4 with an already enabled local APIC. /Mikael --- linux-2.4.13/arch/i386/kernel/apic.c.~1~ Thu Oct 11 13:34:39 2001 +++ linux-2.4.13/arch/i386/kernel/apic.c Sat Oct 27 17:47:49 2001 @@ -588,6 +588,7 @@ goto no_apic; case X86_VENDOR_INTEL: if (boot_cpu_data.x86 == 6 || + (boot_cpu_data.x86 == 15 && cpu_has_apic) || (boot_cpu_data.x86 == 5 && cpu_has_apic)) break; goto no_apic; - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/