On Mon, 2020-02-10 at 09:25 -0800, Matthew Wilcox wrote: > On Mon, Feb 10, 2020 at 12:00:29PM -0500, Qian Cai wrote: > > @@ -2622,7 +2622,7 @@ void filemap_map_pages(struct vm_fault *vmf, > > if (page->index >= max_idx) > > goto unlock; > > > > - if (file->f_ra.mmap_miss > 0) > > + if (data_race(file->f_ra.mmap_miss > 0)) > > file->f_ra.mmap_miss--; > > How is this safe? Two threads can each see 1, and then both decrement the > in-memory copy, causing it to end up at -1. Well, I meant to say it is safe from *data* races rather than all other races, but it is a good catch for the underflow cases and makes some sense to fix them together (so we don't need to touch the same lines over and over again).
