From 60a9887edc3048a3d3f533e910915b65938645c8 Mon Sep 17 00:00:00 2001
From: Jeff Mahoney <jeffm@suse.com>
Date: Tue, 28 Aug 2018 15:21:38 -0400
Subject: [PATCH] btrfs: fix error handling in btrfs_dev_replace_start
Patch-mainline: 4.20-rc1
Git-commit: 5c06147128fbbdf7a84232c5f0d808f53153defe
References: bsc#1107535

When we fail to start a transaction in btrfs_dev_replace_start,
we leave dev_replace->replace_start set to STARTED but clear
->srcdev and ->tgtdev.  Later, that can result in an Oops in
btrfs_dev_replace_progress when having state set to STARTED or
SUSPENDED implies that ->srcdev is valid.

Also fix error handling when the state is already STARTED or
SUSPENDED while starting.  That, too, will clear ->srcdev and ->tgtdev
even though it doesn't own them.  This should be an impossible case to
hit since we should be protected by the BTRFS_FS_EXCL_OP bit being set.
Let's add an ASSERT there while we're at it.

Fixes: e93c89c1aaaaa (Btrfs: add new sources for device replace code)
Signed-off-by: Jeff Mahoney <jeffm@suse.com>
---
 fs/btrfs/dev-replace.c |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

--- a/fs/btrfs/dev-replace.c
+++ b/fs/btrfs/dev-replace.c
@@ -346,6 +346,7 @@ int btrfs_dev_replace_start(struct btrfs
 		break;
 	case BTRFS_IOCTL_DEV_REPLACE_STATE_STARTED:
 	case BTRFS_IOCTL_DEV_REPLACE_STATE_SUSPENDED:
+		ASSERT(0);
 		ret = BTRFS_IOCTL_DEV_REPLACE_RESULT_ALREADY_STARTED;
 		goto leave;
 	}
@@ -390,6 +391,10 @@ int btrfs_dev_replace_start(struct btrfs
 	if (IS_ERR(trans)) {
 		ret = PTR_ERR(trans);
 		btrfs_dev_replace_write_lock(dev_replace);
+		dev_replace->replace_state =
+			BTRFS_IOCTL_DEV_REPLACE_STATE_NEVER_STARTED;
+		dev_replace->srcdev = NULL;
+		dev_replace->tgtdev = NULL;
 		goto leave;
 	}
 
@@ -411,8 +416,6 @@ int btrfs_dev_replace_start(struct btrfs
 	return ret;
 
 leave:
-	dev_replace->srcdev = NULL;
-	dev_replace->tgtdev = NULL;
 	btrfs_dev_replace_write_unlock(dev_replace);
 	btrfs_destroy_dev_replace_tgtdev(fs_info, tgt_device);
 	return ret;