[PATCH v2 16/16] iomap: Make readpage synchronous

From: Matthew Wilcox (Oracle)
Date: Fri Oct 09 2020 - 10:31:29 EST


A synchronous readpage lets us report the actual errno instead of
ineffectively setting PageError.

Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
---
fs/iomap/buffered-io.c | 74 ++++++++++++++++++++++++------------------
1 file changed, 42 insertions(+), 32 deletions(-)

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index e60f572e1590..887bf871ca9b 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -150,9 +150,6 @@ static void iomap_set_range_uptodate(struct page *page, unsigned off,
unsigned last = (off + len - 1) >> inode->i_blkbits;
unsigned long flags;

- if (PageError(page))
- return;
-
if (!iop) {
SetPageUptodate(page);
return;
@@ -165,42 +162,50 @@ static void iomap_set_range_uptodate(struct page *page, unsigned off,
spin_unlock_irqrestore(&iop->uptodate_lock, flags);
}

-static void
-iomap_read_page_end_io(struct bio_vec *bvec, int error)
+static void iomap_read_page_end_io(struct bio_vec *bvec,
+ struct completion *done, bool error)
{
struct page *page = bvec->bv_page;
struct iomap_page *iop = to_iomap_page(page);

- if (unlikely(error)) {
- ClearPageUptodate(page);
- SetPageError(page);
- } else {
+ if (!error)
iomap_set_range_uptodate(page, bvec->bv_offset, bvec->bv_len);
- }

- if (!iop || atomic_sub_and_test(bvec->bv_len, &iop->read_bytes_pending))
- unlock_page(page);
+ if (!iop ||
+ atomic_sub_and_test(bvec->bv_len, &iop->read_bytes_pending)) {
+ if (done)
+ complete(done);
+ else
+ unlock_page(page);
+ }
}

+struct iomap_readpage_ctx {
+ struct page *cur_page;
+ bool cur_page_in_bio;
+ blk_status_t status;
+ struct bio *bio;
+ struct readahead_control *rac;
+ struct completion done;
+};
+
static void
iomap_read_end_io(struct bio *bio)
{
- int error = blk_status_to_errno(bio->bi_status);
+ struct iomap_readpage_ctx *ctx = bio->bi_private;
struct bio_vec *bvec;
struct bvec_iter_all iter_all;

+ /* Capture the first error */
+ if (ctx && ctx->status == BLK_STS_OK)
+ ctx->status = bio->bi_status;
+
bio_for_each_segment_all(bvec, bio, iter_all)
- iomap_read_page_end_io(bvec, error);
+ iomap_read_page_end_io(bvec, ctx ? &ctx->done : NULL,
+ bio->bi_status != BLK_STS_OK);
bio_put(bio);
}

-struct iomap_readpage_ctx {
- struct page *cur_page;
- bool cur_page_in_bio;
- struct bio *bio;
- struct readahead_control *rac;
-};
-
static void
iomap_read_inline_data(struct inode *inode, struct page *page,
struct iomap *iomap)
@@ -292,6 +297,8 @@ iomap_readpage_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
ctx->bio->bi_opf = REQ_OP_READ;
if (ctx->rac)
ctx->bio->bi_opf |= REQ_RAHEAD;
+ else
+ ctx->bio->bi_private = ctx;
ctx->bio->bi_iter.bi_sector = sector;
bio_set_dev(ctx->bio, iomap->bdev);
ctx->bio->bi_end_io = iomap_read_end_io;
@@ -318,15 +325,17 @@ iomap_readpage(struct page *page, const struct iomap_ops *ops)

trace_iomap_readpage(page->mapping->host, 1);

+ ctx.status = BLK_STS_OK;
+ init_completion(&ctx.done);
+
for (poff = 0; poff < PAGE_SIZE; poff += ret) {
ret = iomap_apply(inode, page_offset(page) + poff,
PAGE_SIZE - poff, 0, ops, &ctx,
iomap_readpage_actor);
- if (ret <= 0) {
- WARN_ON_ONCE(ret == 0);
- SetPageError(page);
+ if (WARN_ON_ONCE(ret == 0))
+ ret = -EIO;
+ if (ret < 0)
break;
- }
}

if (ctx.bio) {
@@ -334,15 +343,16 @@ iomap_readpage(struct page *page, const struct iomap_ops *ops)
WARN_ON_ONCE(!ctx.cur_page_in_bio);
} else {
WARN_ON_ONCE(ctx.cur_page_in_bio);
- unlock_page(page);
+ complete(&ctx.done);
}

- /*
- * Just like mpage_readahead and block_read_full_page we always
- * return 0 and just mark the page as PageError on errors. This
- * should be cleaned up all through the stack eventually.
- */
- return 0;
+ wait_for_completion(&ctx.done);
+ if (ret >= 0)
+ ret = blk_status_to_errno(ctx.status);
+ if (ret == 0)
+ return AOP_UPDATED_PAGE;
+ unlock_page(page);
+ return ret;
}
EXPORT_SYMBOL_GPL(iomap_readpage);

--
2.28.0