[PATCH 5.12 216/242] dm writecache: flush origin device when writing and cache is full

Greg Kroah-Hartman
2021-07-15T19:19:09Z

From: Mikulas Patocka <mpatocka@redhat.com>

commit ee55b92a7391bf871939330f662651b54be51b73 upstream.

Commit d53f1fafec9d086f1c5166436abefdaef30e0363 ("dm writecache: do
direct write if the cache is full") changed dm-writecache, so that it
writes directly to the origin device if the cache is full.
Unfortunately, it doesn't forward flush requests to the origin device,
so that there is a bug where flushes are being ignored.

Fix this by adding missing flush forwarding.

For PMEM mode, we fix this bug by disabling direct writes to the origin
device, because it performs better.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Fixes: d53f1fafec9d ("dm writecache: do direct write if the cache is full")
Cc: stable@vger.kernel.org # v5.7+
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/md/dm-writecache.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)

--- a/drivers/md/dm-writecache.c
+++ b/drivers/md/dm-writecache.c
@@ -1297,8 +1297,12 @@ static int writecache_map(struct dm_targ
writecache_flush(wc);
if (writecache_has_error(wc))
goto unlock_error;
+ if (unlikely(wc->cleaner))
+ goto unlock_remap_origin;
goto unlock_submit;
} else {
+ if (dm_bio_get_target_bio_nr(bio))
+ goto unlock_remap_origin;
writecache_offload_bio(wc, bio);
goto unlock_return;
}
@@ -1377,7 +1381,7 @@ read_next_block:
}
e = writecache_pop_from_freelist(wc, (sector_t)-1);
if (unlikely(!e)) {
- if (!found_entry) {
+ if (!WC_MODE_PMEM(wc) && !found_entry) {
direct_write:
e = writecache_find_entry(wc, bio->bi_iter.bi_sector, WFE_RETURN_FOLLOWING);
if (e) {
@@ -2481,7 +2485,7 @@ overflow:
goto bad;
}

- ti->num_flush_bios = 1;
+ ti->num_flush_bios = WC_MODE_PMEM(wc) ? 1 : 2;
ti->flush_supported = true;
ti->num_discard_bios = 1;