On 08/03/2018 09:33 PM, Nikolay Borisov wrote:

On  3.08.2018 15:45, Anand Jain wrote:

quoted

Its a logical bug if we hit fs_devices::num_devices == 1 and if the
replace is running because, as fs_devices::num_devices counts the in memory
devices, so it should include the replace target which is running as
indicated by the flag. If this happens return the -EINVAL back.

Suggested-by: Nikolay Borisov <redacted>
Signed-off-by: Anand Jain <redacted>
---
Hi,
  As it fixes the BUG_ON I have spun a new patch for this.
  Instead of -EINVAL should we use ASSERT?

  fs/btrfs/volumes.c | 27 ++++++++++++++++++++-------
  1 file changed, 20 insertions(+), 7 deletions(-)

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 7359596ac8eb..ed2399caff80 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c

@@ -1855,9 +1855,11 @@ void btrfs_assign_next_active_device(struct btrfs_device *device,
  }
  
  /* Returns btrfs_fs_devices::num_devices minus replace device if any */
-static u64 btrfs_num_devices(struct btrfs_fs_info *fs_info)
+static int btrfs_num_devices(struct btrfs_fs_info *fs_info, u64 *num_devices)

Why do you resort to this travesty of returning the value in an input
parameter? Having the function return int, assuming that we will always
have a positive device num and in case of an error return a negative
value. In the worst case when we get to see a btrfs fs consisting of 2
billion devices then we can start worrying that an int here won't do it.

  Its theoretically wrong. I wonder if David is OK with this? Will wait
  for his comments.

quoted

  {
-	u64 num_devices = fs_info->fs_devices->num_devices;
+	int ret = 0;
+
+	*num_devices = fs_info->fs_devices->num_devices;
  
  	/*
  	 * balance and replace co-exists in a scenario as below..

@@ -1867,12 +1869,13 @@ static u64 btrfs_num_devices(struct btrfs_fs_info *fs_info)
  	 */
  	btrfs_dev_replace_read_lock(&fs_info->dev_replace);
  	if (btrfs_dev_replace_is_ongoing(&fs_info->dev_replace)) {
-		BUG_ON(num_devices < 1);
-		num_devices--;
+		if (*num_devices < 1)
+			ret = -EINVAL;
+		(*num_devices)--;
  	}
  	btrfs_dev_replace_read_unlock(&fs_info->dev_replace);
  
-	return num_devices;
+	return ret;
  }
  
  int btrfs_rm_device(struct btrfs_fs_info *fs_info, const char *device_path,

@@ -1886,7 +1889,12 @@ int btrfs_rm_device(struct btrfs_fs_info *fs_info, const char *device_path,
  
  	mutex_lock(&uuid_mutex);
  
-	num_devices = btrfs_num_devices(fs_info);
+	ret = btrfs_num_devices(fs_info, &num_devices);
+	if (ret) {

The canonical form, used across the whole code base of btrfs, for
checking for an error is 'if (ret <0)' as such please stick to it in
this and all future patches.

  Not a big deal will fix.

(I have a vague recollection this is not the first time I have given you
this feedback)

quoted

+		btrfs_err(fs_info, "logical bug num_devices %llu < 0",
+			  num_devices);
+		return ret;
+	}
  
  	ret = btrfs_check_raid_min_devices(fs_info, num_devices - 1);
  	if (ret)

@@ -3755,7 +3763,12 @@ int btrfs_balance(struct btrfs_fs_info *fs_info,
  		}
  	}
  
-	num_devices = btrfs_num_devices(fs_info);
+	ret = btrfs_num_devices(fs_info, &num_devices);
+	if (ret) {

ditto

  ok.

Thanks, Anand

quoted

+		btrfs_err(fs_info, "hits a logical bug num_devices %llu < 0",
+			  num_devices);
+		return ret;
+	}
  
  	allowed = BTRFS_AVAIL_ALLOC_BIT_SINGLE | BTRFS_BLOCK_GROUP_DUP;
  	if (num_devices > 1)

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