> On Feb 6, 2020, at 3:20 PM, Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote: > > On Thu, Feb 06, 2020 at 01:30:00PM -0500, Qian Cai wrote: >> Both the read and write are done only with the non-exclusive mmap_sem >> held. Since the read only check for a specific bit range (up to 3 bits) >> in the flag but the write here never change those 3 bits, so load >> tearing would be harmless here. Thus, just mark it as an intentional >> data races using the data_race() macro which is designed for those >> situations [1]. > > This changelog makes me think you don't really understand the situation. > > A page never changes its zone number. The zone number happens to be > stored in the same word as other bits which are modified, but the zone > number bits will never be modified by any other write. So we can accept > a reload of the zone bits after an intervening write and we don't need > to use READ_ONCE(). Maybe your explanation is better, but I did try to explain the same thing. I’ll let Andrew to decide if he would like to update the commit log a bit with your wording.
