On Mon, Jan 31, 2022 at 08:02:55PM -0300, Mauricio Faria de Oliveira wrote: > Well, blkdev_direct_IO() gets references for all pages, and on READ > operations it only sets them dirty _later_. > > So, if MADV_FREE'd pages (i.e., not dirty) are used as buffers for > direct IO read from block devices, and page reclaim happens during > __blkdev_direct_IO[_simple]() exactly AFTER bio_iov_iter_get_pages() > returns, but BEFORE the pages are set dirty, the situation happens. > > The direct IO read eventually completes. Now, when userspace reads > the buffers, the PTE is no longer there and the page fault handler > do_anonymous_page() services that with the zero-page, NOT the data! So why not just set the pages dirty early like the other direct I/O implementations? Or if this is fine with the patch should we remove the early dirtying elsewhere? > Reproducer: > ========== > > @ test.c (simplified, but works) Can you add this to blktests or some other regularly run regression test suite? > + smp_rmb(); > + > + /* > + * The only page refs must be from the isolation > + * plus one or more rmap's (dropped by discard:). Overly long line. > + */ > + if ((ref_count == 1 + map_count) && No need for the inner braces.
