diff mbox series

[2/2] fs: Make mpage_readpage synchronous

Message ID 20201016161426.21715-3-willy@infradead.org (mailing list archive)
State New, archived
Headers show
Series Killable synchronous BIO submission | expand

Commit Message

Matthew Wilcox Oct. 16, 2020, 4:14 p.m. UTC 
A synchronous readpage lets us report the actual errno instead of
ineffectively setting PageError.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 fs/mpage.c | 25 ++++++++++++++++++++++---
 1 file changed, 22 insertions(+), 3 deletions(-)

Comments

Keith Busch Oct. 16, 2020, 4:56 p.m. UTC | #1 
On Fri, Oct 16, 2020 at 05:14:26PM +0100, Matthew Wilcox (Oracle) wrote:
> +	err = submit_bio_killable(args.bio, mpage_end_io);
> +	if (unlikely(err))
> +		goto err;
> +
> +	SetPageUptodate(page);

On success, isn't the page already set up to date through the
mpage_end_io() callback?
Matthew Wilcox Oct. 16, 2020, 4:59 p.m. UTC | #2 
On Fri, Oct 16, 2020 at 09:56:08AM -0700, Keith Busch wrote:
> On Fri, Oct 16, 2020 at 05:14:26PM +0100, Matthew Wilcox (Oracle) wrote:
> > +	err = submit_bio_killable(args.bio, mpage_end_io);
> > +	if (unlikely(err))
> > +		goto err;
> > +
> > +	SetPageUptodate(page);
> 
> On success, isn't the page already set up to date through the
> mpage_end_io() callback?

On success, mpage_end_io() isn't called.  And we don't want it to be
because we don't want the page to be unlocked.  I should probably have
included a reference to
https://lore.kernel.org/linux-fsdevel/20201016160443.18685-1-willy@infradead.org/
diff mbox series

Patch

diff --git a/fs/mpage.c b/fs/mpage.c
index 830e6cc2a9e7..88aba79a1861 100644
--- a/fs/mpage.c
+++ b/fs/mpage.c
@@ -406,11 +406,30 @@  int mpage_readpage(struct page *page, get_block_t get_block)
 		.nr_pages = 1,
 		.get_block = get_block,
 	};
+	int err;
 
 	args.bio = do_mpage_readpage(&args);
-	if (args.bio)
-		mpage_bio_submit(REQ_OP_READ, 0, args.bio);
-	return 0;
+	/*
+	 * XXX: We can't tell the difference between "fell back to
+	 * block_read_full_page" and "this was a hole".  If we could,
+	 * we'd avoid unlocking the page in do_mpage_readpage() and
+	 * return AOP_UPDATED_PAGE here.
+	 */
+	if (!args.bio)
+		return 0;
+	bio_set_op_attrs(args.bio, REQ_OP_READ, 0);
+	guard_bio_eod(args.bio);
+	err = submit_bio_killable(args.bio, mpage_end_io);
+	if (unlikely(err))
+		goto err;
+
+	SetPageUptodate(page);
+	return AOP_UPDATED_PAGE;
+
+err:
+	if (err != -ERESTARTSYS)
+		unlock_page(page);
+	return err;
 }
 EXPORT_SYMBOL(mpage_readpage);