| Message ID | 20171018134022.25282-1-mark.rutland@arm.com |
|---|---|
| State | New |
| Headers | show |
| Series | [v3.16.y] percpu: make this_cpu_generic_read() atomic w.r.t. interrupts | expand |
On Wed, Oct 18, 2017 at 02:40:22PM +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 v3.16.y] You sent 2 patches for 3.16.y, did you mean for one of these to be for 3.18.y? thanks, greg k-h
On Thu, Oct 19, 2017 at 11:24:34AM +0200, Greg KH wrote: > You sent 2 patches for 3.16.y, did you mean for one of these to be for > 3.18.y? Sorry; I got a bit muddled and thought I hadn't sent the first copy. Please ignore the duplicate! I'd ignored 3.18.y as EOL, and neither was intended for 3.18.y. Sorry for the noise! Mark.
diff --git a/include/linux/percpu.h b/include/linux/percpu.h index 8419053d0f2e..37ff713a7c7f 100644 --- a/include/linux/percpu.h +++ b/include/linux/percpu.h @@ -276,12 +276,33 @@ do { \ * used. */ -#define _this_cpu_generic_read(pcp) \ -({ typeof(pcp) ret__; \ +#define __this_cpu_generic_read_nopreempt(pcp) \ +({ \ + typeof(pcp) __ret; \ preempt_disable(); \ - ret__ = *this_cpu_ptr(&(pcp)); \ + __ret = ACCESS_ONCE(*raw_cpu_ptr(&(pcp))); \ preempt_enable(); \ - ret__; \ + __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; \ }) #ifndef this_cpu_read