dm verity: have verify_wq use WQ_HIGHPRI if "try_verify_in_tasklet"

Allow verify_wq to preempt softirq since verification in tasklet will
fall-back to using it for error handling (or if the bufio cache
doesn't have required hashes).

Suggested-by: Nathan Huckleberry <nhuck@google.com>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>

Author: Mike Snitzer

drivers/md/dm-verity-target.c

@@ -1151,6 +1151,7 @@ static int verity_ctr(struct dm_target *ti, unsigned argc, char **argv)
 	struct dm_verity_sig_opts verify_args = {0};
 	struct dm_arg_set as;
 	unsigned int num;
+	unsigned int wq_flags;
 	unsigned long long num_ll;
 	int r;
 	int i;
@@ -1388,7 +1389,16 @@ static int verity_ctr(struct dm_target *ti, unsigned argc, char **argv)
 	}
 
 	/* WQ_UNBOUND greatly improves performance when running on ramdisk */
-	v->verify_wq = alloc_workqueue("kverityd", WQ_MEM_RECLAIM | WQ_UNBOUND, num_online_cpus());
+	wq_flags = WQ_MEM_RECLAIM | WQ_UNBOUND;
+	if (v->use_tasklet) {
+		/*
+		 * Allow verify_wq to preempt softirq since verification in
+		 * tasklet will fall-back to using it for error handling
+		 * (or if the bufio cache doesn't have required hashes).
+		 */
+		wq_flags |= WQ_HIGHPRI;
+	}
+	v->verify_wq = alloc_workqueue("kverityd", wq_flags, num_online_cpus());
 	if (!v->verify_wq) {
 		ti->error = "Cannot allocate workqueue";
 		r = -ENOMEM;