On Tue, 2020-09-22 at 18:05 +0100, Matthew Wilcox wrote: > On Tue, Sep 22, 2020 at 12:23:45PM -0400, Qian Cai wrote: > > On Fri, 2020-09-11 at 00:47 +0100, Matthew Wilcox (Oracle) wrote: > > > Size the uptodate array dynamically to support larger pages in the > > > page cache. With a 64kB page, we're only saving 8 bytes per page today, > > > but with a 2MB maximum page size, we'd have to allocate more than 4kB > > > per page. Add a few debugging assertions. > > > > > > Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx> > > > Reviewed-by: Dave Chinner <dchinner@xxxxxxxxxx> > > > > Some syscall fuzzing will trigger this on powerpc: > > > > .config: https://gitlab.com/cailca/linux-mm/-/blob/master/powerpc.config > > > > [ 8805.895344][T445431] WARNING: CPU: 61 PID: 445431 at fs/iomap/buffered- > > io.c:78 iomap_page_release+0x250/0x270 > > Well, I'm glad it triggered. That warning is: > WARN_ON_ONCE(bitmap_full(iop->uptodate, nr_blocks) != > PageUptodate(page)); > so there was definitely a problem of some kind. > > truncate_cleanup_page() calls > do_invalidatepage() calls > iomap_invalidatepage() calls > iomap_page_release() > > Is this the first warning? I'm wondering if maybe there was an I/O error > earlier which caused PageUptodate to get cleared again. If it's easy to > reproduce, perhaps you could try something like this? Yes, this is the first warning. BTW, I did run the reproducer of a805c111650c ("iomap: fix WARN_ON_ONCE() from unprivileged users") earlier, so I am wondering if this is just another victim WARN_ON_ONCE() from it. > > +void dump_iomap_page(struct page *page, const char *reason) > +{ > + struct iomap_page *iop = to_iomap_page(page); > + unsigned int nr_blocks = i_blocks_per_page(page->mapping->host, page); > + > + dump_page(page, reason); > + if (iop) > + printk("iop:reads %d writes %d uptodate %*pb\n", > + atomic_read(&iop->read_bytes_pending), > + atomic_read(&iop->write_bytes_pending), > + nr_blocks, iop->uptodate); > + else > + printk("iop:none\n"); > +} > > and then do something like: > > if (bitmap_full(iop->uptodate, nr_blocks) != PageUptodate(page)) > dump_iomap_page(page, NULL); >
