[Xen-devel] [PATCH] linux/x86: eliminate nesting of run-queue locks inside xtime_lock

["Jan Beulich" <JBeulich@xxxxxxxxxx>]

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>
Cc: Ian Campbell <ian.campbell@xxxxxxxxxx>

--- a/arch/i386/kernel/time-xen.c
+++ b/arch/i386/kernel/time-xen.c
@@ -666,6 +666,7 @@ 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);
 
@@ -720,12 +721,14 @@ 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.
         * HACK: Passing NULL to account_steal_time()

Attachment: xenlinux-x86-clock-was-set-work.patch
Description: Text document

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