CVE-2026-90385

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

md/raid1: create serial pool adding rdev to array with serialize_policy=1

The following bug has been observed with kernel 7.1.3 after adding a new
rdev to an existing RAID1 array with serialize_policy enabled:

  Oops: 0002 [#1]
  CPU: 0 UID: 0 PID: 19639 Comm: ext4lazyinit Not tainted 7.1.3-1-default
  RIP: _raw_spin_lock_irqsave+0x27/0x50
  CR2: 0000000000004960
  Call Trace:
   wait_for_serialization+0xb9/0x260 [raid1]
   raid1_make_request+0x762/0xaff [raid1]
   md_handle_request+0x1c9/0x2e0 [md_mod]

The raid1.c code calls wait_for_serialization() if the MD_SERIALIZE_POLICY
is set, and wait_for_serialization assumes that rdev->serial is
initialized. Normally this will be the case for arrays that have
the serialize_policy sysfs attribute set to 1.

But when a new rdev is added to an existing array in bind_rdev_to_array(),
the condition at mddev_create_serial_pool() causes creation of rdev->serial
to be skipped. Fix it.