This is a note to let you know that I've just added the patch titled
percpu: make this_cpu_generic_read() atomic w.r.t. interrupts
to the 4.4-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:
percpu-make-this_cpu_generic_read-atomic-w.r.t.-interrupts.patch
and it can be found in the queue-4.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From e88d62cd4b2f0b1ae55e9008e79c2794b1fc914d Mon Sep 17 00:00:00 2001
From: Mark Rutland <mark.rutland@xxxxxxx>
Date: Tue, 26 Sep 2017 12:41:52 +0100
Subject: percpu: make this_cpu_generic_read() atomic w.r.t. interrupts
From: Mark Rutland <mark.rutland@xxxxxxx>
commit e88d62cd4b2f0b1ae55e9008e79c2794b1fc914d upstream.
As raw_cpu_generic_read() is a plain read from a raw_cpu_ptr() address,
it's possible (albeit unlikely) that the compiler will split the access
across multiple instructions.
In this_cpu_generic_read() we disable preemption but not interrupts
before calling raw_cpu_generic_read(). Thus, an interrupt could be taken
in the middle of the split load instructions. If a this_cpu_write() or
RMW this_cpu_*() op is made to the same variable in the interrupt
handling path, this_cpu_read() will return a torn value.
For native word types, we can avoid tearing using READ_ONCE(), but this
won't work in all cases (e.g. 64-bit types on most 32-bit platforms).
This patch reworks this_cpu_generic_read() to use READ_ONCE() where
possible, otherwise falling back to disabling interrupts.
Signed-off-by: Mark Rutland <mark.rutland@xxxxxxx>
Cc: Arnd Bergmann <arnd@xxxxxxxx>
Cc: Christoph Lameter <cl@xxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Pranith Kumar <bobby.prani@xxxxxxxxx>
Cc: Tejun Heo <tj@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: linux-arch@xxxxxxxxxxxxxxx
Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
[Mark: backport to v4.4.y]
Signed-off-by: Mark Rutland <mark.rutland@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
include/asm-generic/percpu.h | 24 ++++++++++++++++++++++--
1 file changed, 22 insertions(+), 2 deletions(-)
--- a/include/asm-generic/percpu.h
+++ b/include/asm-generic/percpu.h
@@ -105,15 +105,35 @@ do { \
(__ret); \
})
-#define this_cpu_generic_read(pcp) \
+#define __this_cpu_generic_read_nopreempt(pcp) \
({ \
typeof(pcp) __ret; \
preempt_disable(); \
- __ret = *this_cpu_ptr(&(pcp)); \
+ __ret = READ_ONCE(*raw_cpu_ptr(&(pcp))); \
preempt_enable(); \
__ret; \
})
+#define __this_cpu_generic_read_noirq(pcp) \
+({ \
+ typeof(pcp) __ret; \
+ unsigned long __flags; \
+ raw_local_irq_save(__flags); \
+ __ret = *raw_cpu_ptr(&(pcp)); \
+ raw_local_irq_restore(__flags); \
+ __ret; \
+})
+
+#define this_cpu_generic_read(pcp) \
+({ \
+ typeof(pcp) __ret; \
+ if (__native_word(pcp)) \
+ __ret = __this_cpu_generic_read_nopreempt(pcp); \
+ else \
+ __ret = __this_cpu_generic_read_noirq(pcp); \
+ __ret; \
+})
+
#define this_cpu_generic_to_op(pcp, val, op) \
do { \
unsigned long __flags; \
Patches currently in stable-queue which might be from mark.rutland@xxxxxxx are
queue-4.4/percpu-make-this_cpu_generic_read-atomic-w.r.t.-interrupts.patch