* [PATCH v3.16.y] percpu: make this_cpu_generic_read() atomic w.r.t. interrupts
@ 2017-10-18 13:35 Mark Rutland
0 siblings, 0 replies; 6+ messages in thread
From: Mark Rutland @ 2017-10-18 13:35 UTC (permalink / raw)
To: stable
Cc: Mark Rutland, Arnd Bergmann, Christoph Lameter, Peter Zijlstra,
Pranith Kumar, Tejun Heo, Thomas Gleixner, linux-arch
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@arm.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Christoph Lameter <cl@linux.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Pranith Kumar <bobby.prani@gmail.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-arch@vger.kernel.org
Cc: stable@vger.kernel.org
Signed-off-by: Tejun Heo <tj@kernel.org>
[Mark: backport to v3.16.y]
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
---
include/linux/percpu.h | 29 +++++++++++++++++++++++++----
1 file changed, 25 insertions(+), 4 deletions(-)
diff --git a/include/linux/percpu.h b/include/linux/percpu.h
index 8419053d0f2e..37ff713a7c7f 100644
--- a/include/linux/percpu.h
+++ b/include/linux/percpu.h
@@ -276,12 +276,33 @@ do { \
* used.
*/
-#define _this_cpu_generic_read(pcp) \
-({ typeof(pcp) ret__; \
+#define __this_cpu_generic_read_nopreempt(pcp) \
+({ \
+ typeof(pcp) __ret; \
preempt_disable(); \
- ret__ = *this_cpu_ptr(&(pcp)); \
+ __ret = ACCESS_ONCE(*raw_cpu_ptr(&(pcp))); \
preempt_enable(); \
- ret__; \
+ __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; \
})
#ifndef this_cpu_read
--
2.11.0
^ permalink raw reply related [flat|nested] 6+ messages in thread
* [PATCH v3.16.y] percpu: make this_cpu_generic_read() atomic w.r.t. interrupts
@ 2017-10-18 13:40 Mark Rutland
2017-10-18 13:40 ` Mark Rutland
2017-10-19 9:24 ` Greg KH
0 siblings, 2 replies; 6+ messages in thread
From: Mark Rutland @ 2017-10-18 13:40 UTC (permalink / raw)
To: stable
Cc: Mark Rutland, Arnd Bergmann, Christoph Lameter, Peter Zijlstra,
Pranith Kumar, Tejun Heo, Thomas Gleixner, linux-arch
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@arm.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Christoph Lameter <cl@linux.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Pranith Kumar <bobby.prani@gmail.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-arch@vger.kernel.org
Cc: stable@vger.kernel.org
Signed-off-by: Tejun Heo <tj@kernel.org>
[Mark: backport to v3.16.y]
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
---
include/linux/percpu.h | 29 +++++++++++++++++++++++++----
1 file changed, 25 insertions(+), 4 deletions(-)
diff --git a/include/linux/percpu.h b/include/linux/percpu.h
index 8419053d0f2e..37ff713a7c7f 100644
--- a/include/linux/percpu.h
+++ b/include/linux/percpu.h
@@ -276,12 +276,33 @@ do { \
* used.
*/
-#define _this_cpu_generic_read(pcp) \
-({ typeof(pcp) ret__; \
+#define __this_cpu_generic_read_nopreempt(pcp) \
+({ \
+ typeof(pcp) __ret; \
preempt_disable(); \
- ret__ = *this_cpu_ptr(&(pcp)); \
+ __ret = ACCESS_ONCE(*raw_cpu_ptr(&(pcp))); \
preempt_enable(); \
- ret__; \
+ __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; \
})
#ifndef this_cpu_read
--
2.11.0
^ permalink raw reply related [flat|nested] 6+ messages in thread
* [PATCH v3.16.y] percpu: make this_cpu_generic_read() atomic w.r.t. interrupts
2017-10-18 13:40 Mark Rutland
@ 2017-10-18 13:40 ` Mark Rutland
2017-10-19 9:24 ` Greg KH
1 sibling, 0 replies; 6+ messages in thread
From: Mark Rutland @ 2017-10-18 13:40 UTC (permalink / raw)
To: stable
Cc: Mark Rutland, Arnd Bergmann, Christoph Lameter, Peter Zijlstra,
Pranith Kumar, Tejun Heo, Thomas Gleixner, linux-arch
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@arm.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Christoph Lameter <cl@linux.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Pranith Kumar <bobby.prani@gmail.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-arch@vger.kernel.org
Cc: stable@vger.kernel.org
Signed-off-by: Tejun Heo <tj@kernel.org>
[Mark: backport to v3.16.y]
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
---
include/linux/percpu.h | 29 +++++++++++++++++++++++++----
1 file changed, 25 insertions(+), 4 deletions(-)
diff --git a/include/linux/percpu.h b/include/linux/percpu.h
index 8419053d0f2e..37ff713a7c7f 100644
--- a/include/linux/percpu.h
+++ b/include/linux/percpu.h
@@ -276,12 +276,33 @@ do { \
* used.
*/
-#define _this_cpu_generic_read(pcp) \
-({ typeof(pcp) ret__; \
+#define __this_cpu_generic_read_nopreempt(pcp) \
+({ \
+ typeof(pcp) __ret; \
preempt_disable(); \
- ret__ = *this_cpu_ptr(&(pcp)); \
+ __ret = ACCESS_ONCE(*raw_cpu_ptr(&(pcp))); \
preempt_enable(); \
- ret__; \
+ __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; \
})
#ifndef this_cpu_read
--
2.11.0
^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: [PATCH v3.16.y] percpu: make this_cpu_generic_read() atomic w.r.t. interrupts
2017-10-18 13:40 Mark Rutland
2017-10-18 13:40 ` Mark Rutland
@ 2017-10-19 9:24 ` Greg KH
2017-10-30 14:40 ` Mark Rutland
1 sibling, 1 reply; 6+ messages in thread
From: Greg KH @ 2017-10-19 9:24 UTC (permalink / raw)
To: Mark Rutland
Cc: stable, Arnd Bergmann, Christoph Lameter, Peter Zijlstra,
Pranith Kumar, Tejun Heo, Thomas Gleixner, linux-arch
On Wed, Oct 18, 2017 at 02:40:22PM +0100, Mark Rutland wrote:
> 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@arm.com>
> Cc: Arnd Bergmann <arnd@arndb.de>
> Cc: Christoph Lameter <cl@linux.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Pranith Kumar <bobby.prani@gmail.com>
> Cc: Tejun Heo <tj@kernel.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: linux-arch@vger.kernel.org
> Cc: stable@vger.kernel.org
> Signed-off-by: Tejun Heo <tj@kernel.org>
> [Mark: backport to v3.16.y]
You sent 2 patches for 3.16.y, did you mean for one of these to be for
3.18.y?
thanks,
greg k-h
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH v3.16.y] percpu: make this_cpu_generic_read() atomic w.r.t. interrupts
2017-10-19 9:24 ` Greg KH
@ 2017-10-30 14:40 ` Mark Rutland
2017-10-30 14:40 ` Mark Rutland
0 siblings, 1 reply; 6+ messages in thread
From: Mark Rutland @ 2017-10-30 14:40 UTC (permalink / raw)
To: Greg KH
Cc: stable, Arnd Bergmann, Christoph Lameter, Peter Zijlstra,
Pranith Kumar, Tejun Heo, Thomas Gleixner, linux-arch
On Thu, Oct 19, 2017 at 11:24:34AM +0200, Greg KH wrote:
> You sent 2 patches for 3.16.y, did you mean for one of these to be for
> 3.18.y?
Sorry; I got a bit muddled and thought I hadn't sent the first copy.
Please ignore the duplicate!
I'd ignored 3.18.y as EOL, and neither was intended for 3.18.y.
Sorry for the noise!
Mark.
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH v3.16.y] percpu: make this_cpu_generic_read() atomic w.r.t. interrupts
2017-10-30 14:40 ` Mark Rutland
@ 2017-10-30 14:40 ` Mark Rutland
0 siblings, 0 replies; 6+ messages in thread
From: Mark Rutland @ 2017-10-30 14:40 UTC (permalink / raw)
To: Greg KH
Cc: stable, Arnd Bergmann, Christoph Lameter, Peter Zijlstra,
Pranith Kumar, Tejun Heo, Thomas Gleixner, linux-arch
On Thu, Oct 19, 2017 at 11:24:34AM +0200, Greg KH wrote:
> You sent 2 patches for 3.16.y, did you mean for one of these to be for
> 3.18.y?
Sorry; I got a bit muddled and thought I hadn't sent the first copy.
Please ignore the duplicate!
I'd ignored 3.18.y as EOL, and neither was intended for 3.18.y.
Sorry for the noise!
Mark.
^ permalink raw reply [flat|nested] 6+ messages in thread
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