This is a note to let you know that I've just added the patch titled
btrfs: avoid unnecessary device path update for the same device
to the 6.12-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
btrfs-avoid-unnecessary-device-path-update-for-the-s.patch
and it can be found in the queue-6.12 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 38779dd37b4a69569ddf4e2f5ffce5df4e600dc9
Author: Qu Wenruo <wqu@xxxxxxxx>
Date: Tue Sep 24 12:52:17 2024 +0930
btrfs: avoid unnecessary device path update for the same device
[ Upstream commit 2e8b6bc0ab41ce41e6dfcc204b6cc01d5abbc952 ]
[PROBLEM]
It is very common for udev to trigger device scan, and every time a
mounted btrfs device got re-scan from different soft links, we will get
some of unnecessary device path updates, this is especially common
for LVM based storage:
# lvs
scratch1 test -wi-ao---- 10.00g
scratch2 test -wi-a----- 10.00g
scratch3 test -wi-a----- 10.00g
scratch4 test -wi-a----- 10.00g
scratch5 test -wi-a----- 10.00g
test test -wi-a----- 10.00g
# mkfs.btrfs -f /dev/test/scratch1
# mount /dev/test/scratch1 /mnt/btrfs
# dmesg -c
[ 205.705234] BTRFS: device fsid 7be2602f-9e35-4ecf-a6ff-9e91d2c182c9 devid 1 transid 6 /dev/mapper/test-scratch1 (253:4) scanned by mount (1154)
[ 205.710864] BTRFS info (device dm-4): first mount of filesystem 7be2602f-9e35-4ecf-a6ff-9e91d2c182c9
[ 205.711923] BTRFS info (device dm-4): using crc32c (crc32c-intel) checksum algorithm
[ 205.713856] BTRFS info (device dm-4): using free-space-tree
[ 205.722324] BTRFS info (device dm-4): checking UUID tree
So far so good, but even if we just touched any soft link of
"dm-4", we will get quite some unnecessary device path updates.
# touch /dev/mapper/test-scratch1
# dmesg -c
[ 469.295796] BTRFS info: devid 1 device path /dev/mapper/test-scratch1 changed to /dev/dm-4 scanned by (udev-worker) (1221)
[ 469.300494] BTRFS info: devid 1 device path /dev/dm-4 changed to /dev/mapper/test-scratch1 scanned by (udev-worker) (1221)
Such device path rename is unnecessary and can lead to random path
change due to the udev race.
[CAUSE]
Inside device_list_add(), we are using a very primitive way checking if
the device has changed, strcmp().
Which can never handle links well, no matter if it's hard or soft links.
So every different link of the same device will be treated as a different
device, causing the unnecessary device path update.
[FIX]
Introduce a helper, is_same_device(), and use path_equal() to properly
detect the same block device.
So that the different soft links won't trigger the rename race.
Reviewed-by: Filipe Manana <fdmanana@xxxxxxxx>
Link: https://bugzilla.suse.com/show_bug.cgi?id=1230641
Reported-by: Fabian Vogt <fvogt@xxxxxxxx>
Signed-off-by: Qu Wenruo <wqu@xxxxxxxx>
Signed-off-by: David Sterba <dsterba@xxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 920df7585b0d1..5e75a4e3a5be5 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -732,6 +732,42 @@ const u8 *btrfs_sb_fsid_ptr(const struct btrfs_super_block *sb)
return has_metadata_uuid ? sb->metadata_uuid : sb->fsid;
}
+static bool is_same_device(struct btrfs_device *device, const char *new_path)
+{
+ struct path old = { .mnt = NULL, .dentry = NULL };
+ struct path new = { .mnt = NULL, .dentry = NULL };
+ char *old_path = NULL;
+ bool is_same = false;
+ int ret;
+
+ if (!device->name)
+ goto out;
+
+ old_path = kzalloc(PATH_MAX, GFP_NOFS);
+ if (!old_path)
+ goto out;
+
+ rcu_read_lock();
+ ret = strscpy(old_path, rcu_str_deref(device->name), PATH_MAX);
+ rcu_read_unlock();
+ if (ret < 0)
+ goto out;
+
+ ret = kern_path(old_path, LOOKUP_FOLLOW, &old);
+ if (ret)
+ goto out;
+ ret = kern_path(new_path, LOOKUP_FOLLOW, &new);
+ if (ret)
+ goto out;
+ if (path_equal(&old, &new))
+ is_same = true;
+out:
+ kfree(old_path);
+ path_put(&old);
+ path_put(&new);
+ return is_same;
+}
+
/*
* Add new device to list of registered devices
*
@@ -852,7 +888,7 @@ static noinline struct btrfs_device *device_list_add(const char *path,
MAJOR(path_devt), MINOR(path_devt),
current->comm, task_pid_nr(current));
- } else if (!device->name || strcmp(device->name->str, path)) {
+ } else if (!device->name || !is_same_device(device, path)) {
/*
* When FS is already mounted.
* 1. If you are here and if the device->name is NULL that
