[PATCH 3/3] mm/zswap.c: fix two bugs in zswap_writeback_entry()

[Miaohe Lin]

In the ZSWAP_SWAPCACHE_FAIL and ZSWAP_SWAPCACHE_EXIST case, we forgot to
call zpool_unmap_handle() when zpool can't sleep. And we might sleep in
zswap_get_swap_cache_page() while zpool can't sleep. To fix all of these,
zpool_unmap_handle() should be done before zswap_get_swap_cache_page()
when zpool can't sleep.

Fixes: fc6697a89f56 ("mm/zswap: add the flag can_sleep_mapped")
Signed-off-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>
---
 mm/zswap.c | 17 +++++++----------
 1 file changed, 7 insertions(+), 10 deletions(-)

diff --git a/mm/zswap.c b/mm/zswap.c
index c27ce9f2cdf8..7944e3e57e78 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -967,6 +967,13 @@ static int zswap_writeback_entry(struct zpool *pool, unsigned long handle)
 	spin_unlock(&tree->lock);
 	BUG_ON(offset != entry->offset);
 
+	src = (u8 *)zhdr + sizeof(struct zswap_header);
+	if (!zpool_can_sleep_mapped(pool)) {
+		memcpy(tmp, src, entry->length);
+		src = tmp;
+		zpool_unmap_handle(pool, handle);
+	}
+
 	/* try to allocate swap cache page */
 	switch (zswap_get_swap_cache_page(swpentry, &page)) {
 	case ZSWAP_SWAPCACHE_FAIL: /* no memory or invalidate happened */
@@ -982,17 +989,7 @@ static int zswap_writeback_entry(struct zpool *pool, unsigned long handle)
 	case ZSWAP_SWAPCACHE_NEW: /* page is locked */
 		/* decompress */
 		acomp_ctx = raw_cpu_ptr(entry->pool->acomp_ctx);
-
 		dlen = PAGE_SIZE;
-		src = (u8 *)zhdr + sizeof(struct zswap_header);
-
-		if (!zpool_can_sleep_mapped(pool)) {
-
-			memcpy(tmp, src, entry->length);
-			src = tmp;
-
-			zpool_unmap_handle(pool, handle);
-		}
 
 		mutex_lock(acomp_ctx->mutex);
 		sg_init_one(&input, src, entry->length);
-- 
2.23.0