Re: [PATCH] btrfs: handle the BUG_ON in btrfs_num_devices()
From: Nikolay Borisov <hidden>
Date: 2018-08-03 15:29:37
On 3.08.2018 15:45, Anand Jain wrote:
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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.
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{ - 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. (I have a vague recollection this is not the first time I have given you this feedback)
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+ 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
+ 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)