The xarray can return the previous entry at a location. Use this
fact to simplify the brd code when there is no existing page at
a location. This also slighly improves the handling of racy
discards as we now always have a page under RCU protection by the
time we are ready to copy the data.
Signed-off-by: Christoph Hellwig <hch@xxxxxx>
---
drivers/block/brd.c | 89 ++++++++++++++++++---------------------------
1 file changed, 36 insertions(+), 53 deletions(-)
diff --git a/drivers/block/brd.c b/drivers/block/brd.c
index a3725673cf16..1857da901227 100644
--- a/drivers/block/brd.c
+++ b/drivers/block/brd.c
@@ -51,37 +51,6 @@ static struct page *brd_lookup_page(struct brd_device *brd, sector_t sector)
return xa_load(&brd->brd_pages, sector >> PAGE_SECTORS_SHIFT);
}
-/*
- * Insert a new page for a given sector, if one does not already exist.
- */
-static int brd_insert_page(struct brd_device *brd, sector_t sector, gfp_t gfp)
-{
- pgoff_t idx = sector >> PAGE_SECTORS_SHIFT;
- struct page *page;
- int ret = 0;
-
- page = brd_lookup_page(brd, sector);
- if (page)
- return 0;
-
- page = alloc_page(gfp | __GFP_ZERO | __GFP_HIGHMEM);
- if (!page)
- return -ENOMEM;
-
- xa_lock(&brd->brd_pages);
- ret = __xa_insert(&brd->brd_pages, idx, page, gfp);
- if (!ret)
- brd->brd_nr_pages++;
- xa_unlock(&brd->brd_pages);
-
- if (ret < 0) {
- __free_page(page);
- if (ret == -EBUSY)
- ret = 0;
- }
- return ret;
-}
-
/*
* Free all backing store pages and xarray. This must only be called when
* there are no other users of the device.
@@ -109,41 +78,48 @@ static bool brd_rw_bvec(struct brd_device *brd, struct bio *bio)
sector_t sector = bio->bi_iter.bi_sector;
u32 offset = (sector & (PAGE_SECTORS - 1)) << SECTOR_SHIFT;
blk_opf_t opf = bio->bi_opf;
- struct page *page;
+ struct page *page, *ret;
void *kaddr;
+ int err;
bv.bv_len = min_t(u32, bv.bv_len, PAGE_SIZE - offset);
- if (op_is_write(opf)) {
- int err;
-
+ rcu_read_lock();
+ page = brd_lookup_page(brd, sector);
+ if (!page && op_is_write(opf)) {
/*
* Must use NOIO because we don't want to recurse back into the
* block or filesystem layers from page reclaim.
*/
- err = brd_insert_page(brd, sector,
- (opf & REQ_NOWAIT) ? GFP_NOWAIT : GFP_NOIO);
- if (err) {
- if (err == -ENOMEM && (opf & REQ_NOWAIT))
- bio_wouldblock_error(bio);
- else
- bio_io_error(bio);
- return false;
+ gfp_t gfp = (opf & REQ_NOWAIT) ? GFP_NOWAIT : GFP_NOIO;
+
+ rcu_read_unlock();
+ page = alloc_page(gfp | __GFP_ZERO | __GFP_HIGHMEM);
+ if (!page) {
+ err = -ENOMEM;
+ goto out_error;
+ }
+ rcu_read_lock();
+
+ xa_lock(&brd->brd_pages);
+ ret = __xa_store(&brd->brd_pages, sector >> PAGE_SECTORS_SHIFT,
+ page, gfp);
+ if (!ret)
+ brd->brd_nr_pages++;
+ xa_unlock(&brd->brd_pages);
+
+ if (ret) {
+ __free_page(page);
+ err = xa_err(ret);
+ if (err < 0)
+ goto out_error;
+ page = ret;
}
}
- rcu_read_lock();
- page = brd_lookup_page(brd, sector);
-
kaddr = bvec_kmap_local(&bv);
if (op_is_write(opf)) {
- /*
- * Page can be removed by concurrent discard, it's fine to skip
- * the write and user will read zero data if page does not
- * exist.
- */
- if (page)
- memcpy_to_page(page, offset, kaddr, bv.bv_len);
+ memcpy_to_page(page, offset, kaddr, bv.bv_len);
} else {
if (page)
memcpy_from_page(kaddr, page, offset, bv.bv_len);
@@ -155,6 +131,13 @@ static bool brd_rw_bvec(struct brd_device *brd, struct bio *bio)
bio_advance_iter_single(bio, &bio->bi_iter, bv.bv_len);
return true;
+
+out_error:
+ if (err == -ENOMEM && (opf & REQ_NOWAIT))
+ bio_wouldblock_error(bio);
+ else
+ bio_io_error(bio);
+ return false;
}
static void brd_free_one_page(struct rcu_head *head)
--
2.47.2
