On Wed, 12 Dec 2018 10:27:57 -0500 Josef Bacik <jo...@toxicpanda.com> wrote:
> v5->v6:
> - added more comments as per Andrew's suggestion.
> - fixed the fpin leaks in the two error paths that were pointed out.
>
hm,
> --- a/mm/filemap.c~filemap-drop-the-mmap_sem-for-all-blocking-operations-v6
> +++ a/mm/filemap.c
> @@ -2461,7 +2476,8 @@ static struct file *do_sync_mmap_readahe
>
> /*
> * Asynchronous readahead happens when we find the page and PG_readahead,
> - * so we want to possibly extend the readahead further..
> + * so we want to possibly extend the readahead further. We return the file
> that
> + * was pinned if we have to drop the mmap_sem in order to do IO.
> */
> static struct file *do_async_mmap_readahead(struct vm_fault *vmf,
> struct page *page)
> @@ -2545,14 +2561,15 @@ retry_find:
> page = pagecache_get_page(mapping, offset,
> FGP_CREAT|FGP_FOR_MMAP,
> vmf->gfp_mask);
> - if (!page)
> + if (!page) {
> + if (fpin)
> + goto out_retry;
Is this right? If pagecache_get_page() returns NULL we can now return
VM_FAULT_MAJOR|VM_FAULT_RETRY whereas we used to return ENOMEM.
> return vmf_error(-ENOMEM);
> + }
> }
>
> - if (!lock_page_maybe_drop_mmap(vmf, page, &fpin)) {
> - put_page(page);
> - return ret | VM_FAULT_RETRY;
> - }
> + if (!lock_page_maybe_drop_mmap(vmf, page, &fpin))
> + goto out_retry;
>
> /* Did it get truncated? */
> if (unlikely(page->mapping != mapping)) {
