CVE-2026-43288: ext4: move ext4_percpu_param_init() before ext4_mb_init()

In the Linux kernel, the following vulnerability has been resolved:

ext4: move ext4percpuparaminit() before ext4mbinit()

When running kvm-xfstests -c ext4/1k -C 1 generic/383 with the DOUBLECHECK macro defined, the following panic is triggered:

================================================================== EXT4-fs error (device vdc): ext4validateblockbitmap:423: comm mount: bg 0: bad block bitmap checksum BUG: unable to handle page fault for address: ff110000fa2cc000 PGD 3e01067 P4D 3e02067 PUD 0 Oops: Oops: 0000 [#1] SMP NOPTI CPU: 0 UID: 0 PID: 2386 Comm: mount Tainted: G W 6.18.0-gba65a4e7120a-dirty #1152 PREEMPT(none) RIP: 0010:percpucounteraddbatch+0x13/0xa0 Call Trace: <TASK> ext4markgroupbitmapcorrupted+0xcb/0xe0 ext4validateblockbitmap+0x2a1/0x2f0 ext4readblockbitmap+0x33/0x50 mbgroupbbbitmapalloc+0x33/0x80 ext4mbaddgroupinfo+0x190/0x250 ext4mbinitbackend+0x87/0x290 ext4mbinit+0x456/0x640 ext4fillsuper+0x1072/0x1680 ext4fillsuper+0xd3/0x280 gettreebdevflags+0x132/0x1d0 vfsgettree+0x29/0xd0 vfscmdcreate+0x59/0xe0 dosysfsconfig+0x4f6/0x6b0 dosyscall64+0x50/0x1f0 entrySYSCALL64afterhwframe+0x76/0x7e ==================================================================

This issue can be reproduced using the following commands: mkfs.ext4 -F -q -b 1024 /dev/sda 5G tune2fs -O quota,project /dev/sda mount /dev/sda /tmp/test

With DOUBLECHECK defined, mbgroupbbbitmapalloc() reads and validates the block bitmap. When the validation fails, ext4markgroupbitmapcorrupted() attempts to update sbi->sfreeclusterscounter. However, this percpucounter has not been initialized yet at this point, which leads to the panic described above.

Fix this by moving the execution of ext4percpuparaminit() to occur before ext4mbinit(), ensuring the per-CPU counters are initialized before they are used.