On Mon, Feb 10, 2020 at 02:58:17PM -0500, Qian Cai wrote: > On Mon, 2020-02-10 at 21:05 +0300, Kirill A. Shutemov wrote: > > On Mon, Feb 10, 2020 at 09:25:11AM -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. > > > > Right, it is bogus. > > > > Below is my completely untested attempt on fix this. It still allows > > races, but they will only lead to missed accounting, but not underflow. > > Looks good to me. Do you plan to send out an official patch? Feel free to submit it. After testing. -- Kirill A. Shutemov
