| Message ID | 20171018133237.55218-1-mark.rutland@arm.com |
|---|---|
| State | Superseded |
| Headers | show |
| Series | [v4.4.y] percpu: make this_cpu_generic_read() atomic w.r.t. interrupts | expand |
On Wed, Oct 18, 2017 at 02:32:37PM +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 v4.4.y] Now applied, thanks! greg k-h
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; \