linux-kernel - Re: Bisected KVM hang on x86-32 between v3.12 and v3.13

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Date:	Tue, 8 Apr 2014 14:21:28 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Toralf Förster <toralf.foerster@....de>
Cc:	Michele Ballabio <barra_cuda@...amail.com>,
	linux-kernel@...r.kernel.org, fweisbec@...il.com, mingo@...nel.org,
	Steven Rostedt <rostedt@...dmis.org>,
	David Cohen <david.a.cohen@...ux.intel.com>,
	Stefan Bader <stefan.bader@...onical.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Borislav Petkov <bp@...en8.de>
Subject: Re: Bisected KVM hang on x86-32 between v3.12 and v3.13

On Mon, Apr 07, 2014 at 08:56:58PM +0200, Peter Zijlstra wrote:
> On Mon, Apr 07, 2014 at 08:16:24PM +0200, Toralf Förster wrote:
> 
> > v3.14-10353-g2b3a8fd works fine AFAICS
> > (BTW the fix is stable material, right ?)
> 
> I'm fairly sure its not; its a rather invasive series; see:
> 
> 2432e1364bbe x86: Nuke the supervisor_stack field in i386 thread_info
> b807902a88c4 x86: Nuke GET_THREAD_INFO_WITH_ESP() macro for i386
> 0788aa6a23cb x86: Prepare removal of previous_esp from i386 thread_info structure
> 198d208df437 x86: Keep thread_info on thread stack in x86_32
> 
> Let me see if there's anything 'simpler' we can stuff in .13+

OK.. so could someone test the below patch to see if that makes things
work for .13 and .14?

---
 arch/x86/include/asm/preempt.h | 11 +++++++++++
 include/linux/preempt.h        |  4 ++++
 include/linux/thread_info.h    |  2 --
 3 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/preempt.h b/arch/x86/include/asm/preempt.h
index c8b051933b1b..7ada46d8d4d8 100644
--- a/arch/x86/include/asm/preempt.h
+++ b/arch/x86/include/asm/preempt.h
@@ -5,6 +5,17 @@
 #include <asm/percpu.h>
 #include <linux/thread_info.h>
 
+#ifdef CONFIG_X86_32
+/*
+ * i386's current_thread_info() depends on ESP and for interrupt/exception
+ * stacks this doesn't yield the actual task thread_info.
+ *
+ * We hard rely on the fact that all the TIF_NEED_RESCHED bits are
+ * the same, therefore use the slightly more expensive version below.
+ */
+#define tif_need_resched() test_tsk_thread_flag(current, TIF_NEED_RESCHED)
+#endif
+
 DECLARE_PER_CPU(int, __preempt_count);
 
 /*
diff --git a/include/linux/preempt.h b/include/linux/preempt.h
index de83b4eb1642..891c8f8b52fe 100644
--- a/include/linux/preempt.h
+++ b/include/linux/preempt.h
@@ -17,6 +17,10 @@
 
 #include <asm/preempt.h>
 
+#ifndef tif_need_resched
+#define tif_need_resched() test_thread_flag(TIF_NEED_RESCHED)
+#endif
+
 #if defined(CONFIG_DEBUG_PREEMPT) || defined(CONFIG_PREEMPT_TRACER)
 extern void preempt_count_add(int val);
 extern void preempt_count_sub(int val);
diff --git a/include/linux/thread_info.h b/include/linux/thread_info.h
index fddbe2023a5d..a629e4b23217 100644
--- a/include/linux/thread_info.h
+++ b/include/linux/thread_info.h
@@ -118,8 +118,6 @@ static inline __deprecated void set_need_resched(void)
 	 */
 }
 
-#define tif_need_resched() test_thread_flag(TIF_NEED_RESCHED)
-
 #if defined TIF_RESTORE_SIGMASK && !defined HAVE_SET_RESTORE_SIGMASK
 /*
  * An arch can define its own version of set_restore_sigmask() to get the
--
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