From 52a744f6a5adb89c0e6a8fc4245de70ec7ec4db0 Mon Sep 17 00:00:00 2001
From: Richard Yao <ryao@gentoo.org>
Date: Fri, 18 Sep 2015 08:32:52 -0400
Subject: [PATCH] Discard on zvols should not exceed the length of a block

37f9dac592bf5889c3efb305c48ac39b4c7dd140 replaced the end-start
calculation with a cached value, but neglected to update it on discard
operations. This can cause us to discard data not requested, causing
data loss on zvols.

Reported-by: Richard Connon <richard.connon@zynstra.com>
Signed-off-by: Richard Yao <ryao@gentoo.org>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #3798
---
 module/zfs/zvol.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/module/zfs/zvol.c b/module/zfs/zvol.c
index 00f3e709b11a..b34273509a2b 100644
--- a/module/zfs/zvol.c
+++ b/module/zfs/zvol.c
@@ -637,6 +637,7 @@ zvol_discard(struct bio *bio)
 	if (!(bio->bi_rw & REQ_SECURE)) {
 		start = P2ROUNDUP(start, zv->zv_volblocksize);
 		end = P2ALIGN(end, zv->zv_volblocksize);
+		size = end - start;
 	}
 #endif