FROMGIT: dm-verity: use softirq context only when !need_resched()

Further limit verification in softirq (a.k.a. BH) context to cases where
rescheduling of the interrupted task is not pending.

This helps prevent the CPU from spending too long in softirq context.

Note that handle_softirqs() in kernel/softirq.c already stops running
softirqs in this same case.  However, that check is too coarse-grained,
since many I/O requests can be processed in a single BLOCK_SOFTIRQ.

cherry-picked from commit f9ed3121 https://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm.git/ dm-6.16
https://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm.git/commit/?h=dm-6.16&id=f9ed31214e2ac43cd38d1e517e774050b613b8da



Bug: 404475600
Bug: 401036538

Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Change-Id: I015d99c9dfdcf3b601cd76a4c04ed03757edf681