From: Mark Rutland <mark.rutland@arm.com>
Date: Tue, 26 Sep 2017 12:41:52 +0100
Subject: percpu: make this_cpu_generic_read() atomic w.r.t. interrupts
Git-commit: e88d62cd4b2f0b1ae55e9008e79c2794b1fc914d
Patch-mainline: v4.14-rc4
References: bsc#1114279
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>
Acked-by: Borislav Petkov <bp@suse.de>
---
include/asm-generic/percpu.h | 24 ++++++++++++++++++++++--
1 file changed, 22 insertions(+), 2 deletions(-)
diff --git a/include/asm-generic/percpu.h b/include/asm-generic/percpu.h
index 0504ef8f3aa3..976f8ac26665 100644
--- a/include/asm-generic/percpu.h
+++ b/include/asm-generic/percpu.h
@@ -115,15 +115,35 @@ do { \
(__ret); \
})
-#define this_cpu_generic_read(pcp) \
+#define __this_cpu_generic_read_nopreempt(pcp) \
({ \
typeof(pcp) __ret; \
preempt_disable_notrace(); \
- __ret = raw_cpu_generic_read(pcp); \
+ __ret = READ_ONCE(*raw_cpu_ptr(&(pcp))); \
preempt_enable_notrace(); \
__ret; \
})
+#define __this_cpu_generic_read_noirq(pcp) \
+({ \
+ typeof(pcp) __ret; \
+ unsigned long __flags; \
+ raw_local_irq_save(__flags); \
+ __ret = raw_cpu_generic_read(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; \