On Wed, 8 Sep 2021 09:56:06 +0800 Liu Shixin <liushixin2@xxxxxxxxxx> wrote: > KCSAN reports a data-race on v5.10 which also exists on mainline: > > ================================================================== > BUG: KCSAN: data-race in extfrag_for_order+0x33/0x2d0 > > race at unknown origin, with read to 0xffff9ee9bfffab48 of 8 bytes by task 34 on cpu 1: > extfrag_for_order+0x33/0x2d0 > kcompactd+0x5f0/0xce0 > kthread+0x1f9/0x220 > ret_from_fork+0x22/0x30 > > Reported by Kernel Concurrency Sanitizer on: > CPU: 1 PID: 34 Comm: kcompactd0 Not tainted 5.10.0+ #2 > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Ubuntu-1.8.2-1ubuntu1 04/01/2014 > ================================================================== > > Access to zone->free_area[order].nr_free in extfrag_for_order()/frag_show_print() > is lockless. That's intentional and the stats are a rough estimate anyway. > Annotate them with data_race(). checkpatch helpfully says WARNING: data_race without comment #40: FILE: mm/vmstat.c:1074: + blocks = data_race(zone->free_area[order].nr_free); can we please add a comment ;)
