[Xen-changelog] [linux-2.6.18-xen] xen/x86: eliminate nesting of run-queue locks inside xtime_lock

["Xen patchbot-linux-2.6.18-xen" <patchbot-linux-2.6.18-xen@xxxxxxxxxxxxxxxxxxx>]

# HG changeset patch
# User Keir Fraser <keir.fraser@xxxxxxxxxx>
# Date 1281451661 -3600
# Node ID 53705d74a41b4d86238e6b275893fba95fd13550
# Parent  566d68f989eec2fa570fd0273a07e79d7702d773
xen/x86: eliminate nesting of run-queue locks inside xtime_lock

From: Zdenek Salvet <salvet@xxxxxxxxxxx>

According to Debian bug 591362 this has been causing problems. While
no proof was given that the inverse lock order does actually occur
anywhere (with interrupts enabled), it is plain unnecessary to take
the risk.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxxxx>
Acked-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
---
 arch/i386/kernel/time-xen.c |    7 +++++--
 1 files changed, 5 insertions(+), 2 deletions(-)

diff -r 566d68f989ee -r 53705d74a41b arch/i386/kernel/time-xen.c
--- a/arch/i386/kernel/time-xen.c       Tue Aug 10 15:46:56 2010 +0100
+++ b/arch/i386/kernel/time-xen.c       Tue Aug 10 15:47:41 2010 +0100
@@ -654,6 +654,7 @@ irqreturn_t timer_interrupt(int irq, voi
        s64 delta, delta_cpu, stolen, blocked;
        u64 sched_time;
        unsigned int i, cpu = smp_processor_id();
+       int schedule_clock_was_set_work = 0;
        struct shadow_time_info *shadow = &per_cpu(shadow_time, cpu);
        struct vcpu_runstate_info *runstate = &per_cpu(runstate, cpu);
 
@@ -715,11 +716,13 @@ irqreturn_t timer_interrupt(int irq, voi
 
        if (shadow_tv_version != HYPERVISOR_shared_info->wc_version) {
                update_wallclock();
-               if (keventd_up())
-                       schedule_work(&clock_was_set_work);
+               schedule_clock_was_set_work = 1;
        }
 
        write_sequnlock(&xtime_lock);
+
+       if (schedule_clock_was_set_work && keventd_up())
+               schedule_work(&clock_was_set_work);
 
        /*
         * Account stolen ticks.

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