diff options
| author | Mark Rutland <mark.rutland@arm.com> | 2017-09-26 12:41:52 +0100 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2017-10-21 17:09:01 +0200 |
| commit | 951ba9f6c8b97043f6ba398d937e7b0d175f2f07 (patch) | |
| tree | 04ad227642dc40e94a31c206efa97bb49846c726 /include | |
| parent | e1fe3813117f465a2db200aebb13969056986c64 (diff) | |
percpu: make this_cpu_generic_read() atomic w.r.t. interrupts
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
Signed-off-by: Tejun Heo <tj@kernel.org>
[Mark: backport to v4.4.y]
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'include')
| -rw-r--r-- | include/asm-generic/percpu.h | 24 |
1 files changed, 22 insertions, 2 deletions
diff --git a/include/asm-generic/percpu.h b/include/asm-generic/percpu.h index 4d9f233c4ba8..7d58ffdacd62 100644 --- 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; \ |