From 0d00e812d9f3780803e390ab52a6963482f0ab1d 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>
---
 module/zfs/zvol.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/module/zfs/zvol.c b/module/zfs/zvol.c
index bcdd8e8def..37c39d19ad 100644
--- a/module/zfs/zvol.c
+++ b/module/zfs/zvol.c
@@ -662,6 +662,7 @@ 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