On Tue, Feb 25, 2020 at 10:58:27PM -0500, Qian Cai wrote: > pgdat->kswapd_classzone_idx could be accessed concurrently in > wakeup_kswapd(). Plain writes and reads without any lock protection > result in data races. Fix them by adding a pair of READ|WRITE_ONCE() as > well as saving a branch (compilers might well optimize the original code > in an unintentional way anyway). While at it, also take care of > pgdat->kswapd_order and non-kswapd threads in allow_direct_reclaim(). I don't understand why the usages of kswapd_classzone_idx in kswapd() and kswapd_try_to_sleep() don't need changing too? kswapd_classzone_idx() looks safe to me, but I'm prone to missing stupid things that compilers are allowed to do.
