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. Avoid this by using READ_ONCE() to inhibit tearing. 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: linux-arch@xxxxxxxxxxxxxxx --- include/asm-generic/percpu.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/include/asm-generic/percpu.h b/include/asm-generic/percpu.h index 0504ef8..79a8a58 100644 --- a/include/asm-generic/percpu.h +++ b/include/asm-generic/percpu.h @@ -67,7 +67,7 @@ #define raw_cpu_generic_read(pcp) \ ({ \ - *raw_cpu_ptr(&(pcp)); \ + READ_ONCE(*raw_cpu_ptr(&(pcp))); \ }) #define raw_cpu_generic_to_op(pcp, val, op) \ -- 1.9.1