On Mon, Dec 11, 2023 at 03:56:16PM +0100, Greg Kroah-Hartman wrote:
On Sat, Dec 09, 2023 at 10:28:36AM -0700, Nathan Chancellor wrote:
On Tue, Dec 05, 2023 at 12:17:31PM +0900, Greg Kroah-Hartman wrote:
5.4-stable review patch. If anyone has any objections, please let me know.
From: Qu Wenruo wqu@suse.com
commit 2db313205f8b96eea467691917138d646bb50aef upstream.
There is a feature request to add dmesg output when unmounting a btrfs. There are several alternative methods to do the same thing, but with their own problems:
Use eBPF to watch btrfs_put_super()/open_ctree() Not end user friendly, they have to dip their head into the source code.
Watch for directory /sys/fs/<uuid>/ This is way more simple, but still requires some simple device -> uuid lookups. And a script needs to use inotify to watch /sys/fs/.
Compared to all these, directly outputting the information into dmesg would be the most simple one, with both device and UUID included.
And since we're here, also add the output when mounting a filesystem for the first time for parity. A more fine grained monitoring of subvolume mounts should be done by another layer, like audit.
Now mounting a btrfs with all default mkfs options would look like this:
[81.906566] BTRFS info (device dm-8): first mount of filesystem 633b5c16-afe3-4b79-b195-138fe145e4f2 [81.907494] BTRFS info (device dm-8): using crc32c (crc32c-intel) checksum algorithm [81.908258] BTRFS info (device dm-8): using free space tree [81.912644] BTRFS info (device dm-8): auto enabling async discard [81.913277] BTRFS info (device dm-8): checking UUID tree [91.668256] BTRFS info (device dm-8): last unmount of filesystem 633b5c16-afe3-4b79-b195-138fe145e4f2
CC: stable@vger.kernel.org # 5.4+ Link: https://github.com/kdave/btrfs-progs/issues/689 Reviewed-by: Anand Jain anand.jain@oracle.com Signed-off-by: Qu Wenruo wqu@suse.com Reviewed-by: David Sterba dsterba@suse.com [ update changelog ] Signed-off-by: David Sterba dsterba@suse.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
fs/btrfs/disk-io.c | 1 + fs/btrfs/super.c | 5 ++++- 2 files changed, 5 insertions(+), 1 deletion(-)
--- a/fs/btrfs/disk-io.c +++ b/fs/btrfs/disk-io.c @@ -2829,6 +2829,7 @@ int open_ctree(struct super_block *sb, goto fail_alloc; }
- btrfs_info(fs_info, "first mount of filesystem %pU", disk_super->fsid);
clang tells me this backport does not appear to be correct and will likely introduce a null pointer deference:
fs/btrfs/disk-io.c:2832:55: warning: variable 'disk_super' is uninitialized when used here [-Wuninitialized] 2832 | btrfs_info(fs_info, "first mount of filesystem %pU", disk_super->fsid); | ^~~~~~~~~~ fs/btrfs/ctree.h:3002:41: note: expanded from macro 'btrfs_info' 3002 | btrfs_printk(fs_info, KERN_INFO fmt, ##args) | ^~~~ fs/btrfs/disk-io.c:2630:38: note: initialize the variable 'disk_super' to silence this warning 2630 | struct btrfs_super_block *disk_super; | ^ | = NULL 1 warning generated.
Thanks for the notice, I've now reverted this.
Thanks. I've verified that this only affects 5.4. The patch is still possible to apply there, the btrfs_info() call would have to be moved after 'disk_super' is initialized. The patch is not that important so reverting is OK for me.