On Tue, Sep 26, 2017 at 12:41:52PM +0100, Mark Rutland wrote: > 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@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: Thomas Gleixner <tglx@xxxxxxxxxxxxx> > Cc: linux-arch@xxxxxxxxxxxxxxx Applied to percpu/for-4.14-fixes. Thanks. -- tejun
