[dm-devel] [PATCH] dm-writecache: allow the underlying device to be shrunk

[Mikulas Patocka <mpatocka@redhat.com>]

Allow shrinking the underlying data device (dm-writecache must be
suspended when the device is shrunk).

This patch modifies dm-writecache, so that it doesn't attempt to write any
data beyond the end of the data device.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Cc: stable@vger.kernel.org

---
 drivers/md/dm-writecache.c |   18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

Index: linux-2.6/drivers/md/dm-writecache.c
===================================================================
--- linux-2.6.orig/drivers/md/dm-writecache.c	2021-02-05 20:30:35.000000000 +0100
+++ linux-2.6/drivers/md/dm-writecache.c	2021-02-09 16:50:36.000000000 +0100
@@ -148,6 +148,7 @@ struct dm_writecache {
 	size_t metadata_sectors;
 	size_t n_blocks;
 	uint64_t seq_count;
+	uint64_t data_device_sectors;
 	void *block_start;
 	struct wc_entry *entries;
 	unsigned block_size;
@@ -969,6 +970,8 @@ static void writecache_resume(struct dm_
 
 	wc_lock(wc);
 
+	wc->data_device_sectors = i_size_read(wc->dev->bdev->bd_inode) >> SECTOR_SHIFT;
+
 	if (WC_MODE_PMEM(wc)) {
 		persistent_memory_invalidate_cache(wc->memory_map, wc->memory_map_size);
 	} else {
@@ -1638,6 +1641,10 @@ static bool wc_add_block(struct writebac
 	void *address = memory_data(wc, e);
 
 	persistent_memory_flush_cache(address, block_size);
+
+	if (unlikely(wb->bio.bi_iter.bi_sector + bio_sectors(&wb->bio) >= wc->data_device_sectors))
+		return true;
+
 	return bio_add_page(&wb->bio, persistent_memory_page(address),
 			    block_size, persistent_memory_page_offset(address)) != 0;
 }
@@ -1709,6 +1716,9 @@ static void __writecache_writeback_pmem(
 		if (writecache_has_error(wc)) {
 			bio->bi_status = BLK_STS_IOERR;
 			bio_endio(bio);
+		} else if (unlikely(!bio_sectors(bio))) {
+			bio->bi_status = BLK_STS_OK;
+			bio_endio(bio);
 		} else {
 			submit_bio(bio);
 		}
@@ -1752,6 +1762,14 @@ static void __writecache_writeback_ssd(s
 			e = f;
 		}
 
+		if (unlikely(to.sector + to.count > wc->data_device_sectors)) {
+			if (to.sector >= wc->data_device_sectors) {
+				writecache_copy_endio(0, 0, c);
+				continue;
+			}
+			from.count = to.count = wc->data_device_sectors - to.sector;
+		}
+
 		dm_kcopyd_copy(wc->dm_kcopyd, &from, 1, &to, 0, writecache_copy_endio, c);
 
 		__writeback_throttle(wc, wbl);

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