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percpu: make this_cpu_generic_read() atomic w.r.t. interrupts 

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>
This commit is contained in:
Mark Rutland 2017-09-26 12:41:52 +01:00 committed by Tejun Heo
parent e365806ac2
commit e88d62cd4b
1 changed files with 22 additions and 2 deletions
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24
include/asm-generic/percpu.h
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@ -115,15 +115,35 @@ do { \
(__ret); \ (__ret); \
}) })
#define this_cpu_generic_read(pcp) \ #define __this_cpu_generic_read_nopreempt(pcp) \
({ \ ({ \
typeof(pcp) __ret; \ typeof(pcp) __ret; \
preempt_disable_notrace(); \ preempt_disable_notrace(); \
__ret = raw_cpu_generic_read(pcp); \ __ret = READ_ONCE(*raw_cpu_ptr(&(pcp))); \
preempt_enable_notrace(); \ preempt_enable_notrace(); \
__ret; \ __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) \ #define this_cpu_generic_to_op(pcp, val, op) \
do { \ do { \
unsigned long __flags; \ unsigned long __flags; \