The patch below does not apply to the 4.14-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 5c06147128fbbdf7a84232c5f0d808f53153defe Mon Sep 17 00:00:00 2001

From: Jeff Mahoney jeffm@suse.com Date: Thu, 6 Sep 2018 15:52:17 -0400 Subject: [PATCH] btrfs: fix error handling in btrfs_dev_replace_start

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) CC: stable@vger.kernel.org # 4.4+ Signed-off-by: Jeff Mahoney jeffm@suse.com Reviewed-by: David Sterba dsterba@suse.com Signed-off-by: David Sterba dsterba@suse.com

diff --git a/fs/btrfs/dev-replace.c b/fs/btrfs/dev-replace.c index 4e2b67d06305..ff01740158aa 100644 --- a/fs/btrfs/dev-replace.c +++ b/fs/btrfs/dev-replace.c @@ -440,6 +440,7 @@ int btrfs_dev_replace_start(struct btrfs_fs_info *fs_info, 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; } @@ -482,6 +483,10 @@ int btrfs_dev_replace_start(struct btrfs_fs_info *fs_info, 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; }

@@ -503,8 +508,6 @@ int btrfs_dev_replace_start(struct btrfs_fs_info *fs_info, return ret;

leave: - dev_replace->srcdev = NULL; - dev_replace->tgtdev = NULL; btrfs_dev_replace_write_unlock(dev_replace); btrfs_destroy_dev_replace_tgtdev(tgt_device); return ret;