[PATCH v2 12/17] bcache: handle cache set verify_ondisk properly for bucket size > 8MB

Coly Li
2020-07-15T05:46:47Z

In bch_btree_cache_alloc() when CONFIG_BCACHE_DEBUG is configured,
allocate memory for c->verify_ondisk may fail if the bucket size > 8MB,
which will require __get_free_pages() to allocate continuous pages
with order > 11 (the default MAX_ORDER of Linux buddy allocator). Such
over size allocation will fail, and cause 2 problems,
- When CONFIG_BCACHE_DEBUG is configured, bch_btree_verify() does not
work, because c->verify_ondisk is NULL and bch_btree_verify() returns
immediately.
- bch_btree_cache_alloc() will fail due to c->verify_ondisk allocation
failed, then the whole cache device registration fails. And because of
this failure, the first problem of bch_btree_verify() has no chance to
be triggered.

This patch fixes the above problem by two means,
1) If pages allocation of c->verify_ondisk fails, set it to NULL and
returns bch_btree_cache_alloc() with -ENOMEM.
2) When calling __get_free_pages() to allocate c->verify_ondisk pages,
use ilog2(meta_bucket_pages(&c->sb)) to make sure ilog2() will always
generate a pages order <= MAX_ORDER (or CONFIG_FORCE_MAX_ZONEORDER).
Then the buddy system won't directly reject the allocation request.

Signed-off-by: Coly Li <colyli@suse.de>
---
drivers/md/bcache/btree.c | 12 ++++++++++--
1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/drivers/md/bcache/btree.c b/drivers/md/bcache/btree.c
index dd116c83de80..79716ac9fb5d 100644
--- a/drivers/md/bcache/btree.c
+++ b/drivers/md/bcache/btree.c
@@ -738,7 +738,7 @@ void bch_btree_cache_free(struct cache_set *c)
if (c->verify_data)
list_move(&c->verify_data->list, &c->btree_cache);

- free_pages((unsigned long) c->verify_ondisk, ilog2(bucket_pages(c)));
+ free_pages((unsigned long) c->verify_ondisk, ilog2(meta_bucket_pages(&c->sb)));
#endif

list_splice(&c->btree_cache_freeable,
@@ -785,7 +785,15 @@ int bch_btree_cache_alloc(struct cache_set *c)
mutex_init(&c->verify_lock);

c->verify_ondisk = (void *)
- __get_free_pages(GFP_KERNEL|__GFP_COMP, ilog2(bucket_pages(c)));
+ __get_free_pages(GFP_KERNEL|__GFP_COMP, ilog2(meta_bucket_pages(&c->sb)));
+ if (!c->verify_ondisk) {
+ /*
+ * Don't worry about the mca_rereserve buckets
+ * allocated in previous for-loop, they will be
+ * handled properly in bch_cache_set_unregister().
+ */
+ return -ENOMEM;
+ }

c->verify_data = mca_bucket_alloc(c, &ZERO_KEY, GFP_KERNEL);

--
2.26.2