[PATCH] zswap: change BUG to WARN in zswap_writeback_entry

[Dan Streetman <ddstreet@ieee.org>]

Change the BUG calls to WARN, and return error.

There's no need to call BUG from this function, as it can safely return
the error.  The only caller of this function is the zpool that zswap is
using, when zswap is trying to reduce the zpool size.  While the error
does indicate a bug, as none of the WARN conditions should ever happen,
the zpool implementation can recover by trying to evict another page
or zswap will recover by sending the new page to the swap disk.

This was reported in kernel bug 192571:
https://bugzilla.kernel.org/show_bug.cgi?id=192571

Reported-by: Gluzskiy Alexandr <sss123next@list.ru>
Signed-off-by: Dan Streetman <ddstreet@ieee.org>
---
 mm/zswap.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/mm/zswap.c b/mm/zswap.c
index 067a0d6..60c4e6f 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -787,7 +787,10 @@ static int zswap_writeback_entry(struct zpool *pool, unsigned long handle)
 		return 0;
 	}
 	spin_unlock(&tree->lock);
-	BUG_ON(offset != entry->offset);
+	if (WARN_ON(offset != entry->offset)) {
+		ret = -EINVAL;
+		goto fail;
+	}
 
 	/* try to allocate swap cache page */
 	switch (zswap_get_swap_cache_page(swpentry, &page)) {
@@ -813,8 +816,13 @@ static int zswap_writeback_entry(struct zpool *pool, unsigned long handle)
 		put_cpu_ptr(entry->pool->tfm);
 		kunmap_atomic(dst);
 		zpool_unmap_handle(entry->pool->zpool, entry->handle);
-		BUG_ON(ret);
-		BUG_ON(dlen != PAGE_SIZE);
+		if (WARN(ret, "error decompressing page: %d\n", ret))
+			goto fail;
+		if (WARN(dlen != PAGE_SIZE,
+			 "decompressed page only %x bytes\n", dlen)) {
+			ret = -EINVAL;
+			goto fail;
+		}
 
 		/* page is up to date */
 		SetPageUptodate(page);
-- 
2.9.3

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