On Wed, May 14, 2014 at 05:40:50AM +0200, Greg KH wrote:
> Peter, Guenter is reporting that the patch below breaks all non-x86
> builds with:
>
> include/asm-generic/preempt.h: In function '__preempt_count_dec_and_test':
> include/asm-generic/preempt.h:71:2: error: implicit declaration of function 'tif_need_resched' [-Werror=implicit-function-declaration]
> return !--*preempt_count_ptr() && tif_need_resched();
>
> Any ideas?
Yeah, I suck :/
Ok, the below seems to build on a number of !x86 archs and still does
build for i386 too.
Now its a little fragile, but since there's only a single
<asm/preempt.h> include (from linux/preempt.h) it should be safe.
Obviously its not actually been tested (as per the tags) because the
patch is different.
---
Subject: x86,preempt: Fix preemption for i386
From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Date: Wed, 9 Apr 2014 16:24:47 +0200
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: Greg KH <greg@xxxxxxxxx>
Cc: bp@xxxxxxxxx
Cc: fweisbec@xxxxxxxxx
Cc: david.a.cohen@xxxxxxxxxxxxxxx
Cc: mingo@xxxxxxxxxx
Cc: fweisbec@xxxxxxxxx
Cc: greg@xxxxxxxxx
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: gregkh@xxxxxxxxxxxxxxxxxxx
Cc: pbonzini@xxxxxxxxxx
Cc: rostedt@xxxxxxxxxxx
Cc: stefan.bader@xxxxxxxxxxxxx
Cc: mingo@xxxxxxxxxx
Cc: toralf.foerster@xxxxxx
Cc: David Cohen <david.a.cohen@xxxxxxxxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: torvalds@xxxxxxxxxxxxxxxxxxxx
Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Cc: David Cohen <david.a.cohen@xxxxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Cc: <stable-commits@xxxxxxxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: peterz@xxxxxxxxxxxxx
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: barra_cuda@xxxxxxxxxxxx
Tested-by: Stefan Bader <stefan.bader@xxxxxxxxxxxxx>
Tested-by: Toralf F�rster <toralf.foerster@xxxxxx>
Tested-by: Michele Ballabio <barra_cuda@xxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/20140409142447.GD13658@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
---
arch/x86/include/asm/preempt.h | 12 ++++++++++++
include/linux/preempt.h | 2 ++
include/linux/thread_info.h | 2 --
3 files changed, 14 insertions(+), 2 deletions(-)
--- a/arch/x86/include/asm/preempt.h
+++ b/arch/x86/include/asm/preempt.h
@@ -5,6 +5,18 @@
#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.
+ */
+#undef tif_need_resched
+#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
@@ -15,6 +15,8 @@
*/
#define PREEMPT_NEED_RESCHED 0x80000000
+#define tif_need_resched() test_thread_flag(TIF_NEED_RESCHED)
+
#include <asm/preempt.h>
#if defined(CONFIG_DEBUG_PREEMPT) || defined(CONFIG_PREEMPT_TRACER)
--- 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
Attachment:
pgpo3DS1aRKuD.pgp
Description: PGP signature