CVE-2025-71225: md: suspend array while updating raid_disks via sysfs

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

md: suspend array while updating raiddisks via sysfs

In raid1reshape(), freezearray() is called before modifying the r1bio memory pool (conf->r1biopool) and conf->raiddisks, and unfreezearray() is called after the update is completed.

However, freezearray() only waits until nrsyncpending and (nrpending - nrqueued) of all buckets reaches zero. When an I/O error occurs, nrqueued is increased and the corresponding r1bio is queued to either retrylist or bioendiolist. As a result, freezearray() may unblock before these r1bios are released.

This can lead to a situation where conf->raiddisks and the mempool have already been updated while queued r1bios, allocated with the old raiddisks value, are later released. Consequently, freer1bio() may access memory out of bounds in putallbios() and release r1bios of the wrong size to the new mempool, potentially causing issues with the mempool as well.

Since only normal I/O might increase nrqueued while an I/O error occurs, suspending the array avoids this issue.

Note: Updating raiddisks via ioctl SETARRAYINFO already suspends the array. Therefore, we suspend the array when updating raiddisks via sysfs to avoid this issue too.