This is a note to let you know that I've just added the patch titled
x86,preempt: Fix preemption for i386
to the 3.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
x86-preempt-fix-preemption-for-i386.patch
and it can be found in the queue-3.14 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From peterz@xxxxxxxxxxxxx Tue May 13 16:56:21 2014
From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Date: Wed, 9 Apr 2014 16:24:47 +0200
Subject: x86,preempt: Fix preemption for i386
To: Stefan Bader <stefan.bader@xxxxxxxxxxxxx>
Cc: Toralf Förster <toralf.foerster@xxxxxx>, Michele Ballabio <barra_cuda@xxxxxxxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx, fweisbec@xxxxxxxxx, mingo@xxxxxxxxxx, Steven Rostedt <rostedt@xxxxxxxxxxx>, David Cohen <david.a.cohen@xxxxxxxxxxxxxxx>, Paolo Bonzini <pbonzini@xxxxxxxxxx>, Borislav Petkov <bp@xxxxxxxxx>, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>, Greg KH <greg@xxxxxxxxx>
Message-ID: <20140409142447.GD13658@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>
Content-Disposition: inline
From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Many people reported preemption/reschedule problems with i386 kernels
for .13 and .14. After Michele bisected this to a combination of
3e8e42c69bb ("sched: Revert need_resched() to look at TIF_NEED_RESCHED")
ded79754754 ("irq: Force hardirq exit's softirq processing on its own stack")
it finally dawned on me that i386's current_thread_info() was to
blame.
When we are on interrupt/exception stacks, we fail to observe the
right TIF_NEED_RESCHED bit and therefore the PREEMPT_NEED_RESCHED
folding malfunctions.
Current upstream fixes this by making i386 behave the same as x86_64
already did:
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")
However, that is far too much to stuff into -stable. Therefore I
propose we merge the below patch which uses task_thread_info(current)
for tif_need_resched() instead of the ESP based current_thread_info().
This makes sure we always observe the one true TIF_NEED_RESCHED bit
and things will work as expected again.
Cc: fweisbec@xxxxxxxxx
Cc: mingo@xxxxxxxxxx
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: David Cohen <david.a.cohen@xxxxxxxxxxxxxxx>
Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Tested-by: Stefan Bader <stefan.bader@xxxxxxxxxxxxx>
Tested-by: Toralf Förster <toralf.foerster@xxxxxx>
Tested-by: Michele Ballabio <barra_cuda@xxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
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(-)
--- 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);
/*
--- 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);
--- a/include/linux/thread_info.h
+++ b/include/linux/thread_info.h
@@ -118,8 +118,6 @@ static inline __deprecated void set_need
*/
}
-#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
Patches currently in stable-queue which might be from peterz@xxxxxxxxxxxxx are
queue-3.14/x86-preempt-fix-preemption-for-i386.patch
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