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Subject[PATCH 3.16 082/305] btrfs: fix error handling in btrfs_dev_replace_start
3.16.63-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Jeff Mahoney <jeffm@suse.com>

commit 5c06147128fbbdf7a84232c5f0d808f53153defe upstream.

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>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
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
@@ -362,6 +362,7 @@ int btrfs_dev_replace_start(struct btrfs
break;
case BTRFS_IOCTL_DEV_REPLACE_STATE_STARTED:
case BTRFS_IOCTL_DEV_REPLACE_STATE_SUSPENDED:
+ ASSERT(0);
args->result = BTRFS_IOCTL_DEV_REPLACE_RESULT_ALREADY_STARTED;
goto leave;
}
@@ -406,6 +407,10 @@ int btrfs_dev_replace_start(struct btrfs
if (IS_ERR(trans)) {
ret = PTR_ERR(trans);
btrfs_dev_replace_lock(dev_replace);
+ dev_replace->replace_state =
+ BTRFS_IOCTL_DEV_REPLACE_STATE_NEVER_STARTED;
+ dev_replace->srcdev = NULL;
+ dev_replace->tgtdev = NULL;
goto leave;
}

@@ -423,8 +428,6 @@ int btrfs_dev_replace_start(struct btrfs
return 0;

leave:
- dev_replace->srcdev = NULL;
- dev_replace->tgtdev = NULL;
btrfs_dev_replace_unlock(dev_replace);
leave_no_lock:
if (tgt_device)
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