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Re: [Xen-devel] [PATCH] Fix deadlock in schedule.c at TRACE mode

To: NISHIGUCHI Naoki <nisiguti@xxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH] Fix deadlock in schedule.c at TRACE mode
From: Atsushi SAKAI <sakaia@xxxxxxxxxxxxxx>
Date: Thu, 24 Apr 2008 14:42:53 +0900
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx
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Hi, Naoki

I have two questions about this.

1)How to reproduce your deadlock ?
  Would you give me your test environment to reproduce this deadlock?
  Is it easily reproduced by running xenmon.py or xentrace 
  with one or two guest domain(s)?
 or Any additional condition needed?

2)About fixing code,
  I think __trace_var() should fix for this issue not schedule()
  This issue cannot be fixed by modify the __trace_var()?

Atsushi SAKAI

NISHIGUCHI Naoki <nisiguti@xxxxxxxxxxxxxx> wrote:

> Hi,
> In schedule.c, schedule() and sched_adjust() call trace functions during
> acquiring lock of schedule_lock in each cpu's schedule_data. When trace
> buffers are enabled, the trace function (__trace_var()) may call
> vcpu_wake() by calling send_guest_global_virq(). In the case, a deadlock
> occurs when acquiring lock of schedule_lock.
> Attached patch fixes this problem.
> Signed-off-by: Naoki Nishiguchi <nisiguti@xxxxxxxxxxxxxx>
> Regards,
> Naoki Nishiguchi

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