fs: replace use of system_wq with system_percpu_wq

Currently if a user enqueue a work item using schedule_delayed_work() the
used wq is "system_wq" (per-cpu wq) while queue_delayed_work() use
WORK_CPU_UNBOUND (used when a cpu is not specified). The same applies to
schedule_work() that is using system_wq and queue_work(), that makes use
again of WORK_CPU_UNBOUND.

This lack of consistentcy cannot be addressed without refactoring the API.

system_wq is a per-CPU worqueue, yet nothing in its name tells about that
CPU affinity constraint, which is very often not required by users.
Make it clear by adding a system_percpu_wq to all the fs subsystem.

The old wq will be kept for a few release cylces.

Suggested-by: Tejun Heo <[e-mail]>
Signed-off-by: Marco Crivellari <[e-mail]>
Link: https://lore.kernel.org/[e-mail]
Signed-off-by: Christian Brauner <[e-mail]>

fs/aio.c

···
 
 	/* Synchronize against RCU protected table->table[] dereferences */
 	INIT_RCU_WORK(&ctx->free_rwork, free_ioctx);
-	queue_rcu_work(system_wq, &ctx->free_rwork);
+	queue_rcu_work(system_percpu_wq, &ctx->free_rwork);
 }
 
 /*

fs/fs-writeback.c

···
 
 	ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
 	if (ret == 0 && write)
-		mod_delayed_work(system_wq, &dirtytime_work, 0);
+		mod_delayed_work(system_percpu_wq, &dirtytime_work, 0);
 	return ret;
 }
 

fs/fuse/dev.c

···
 	    goto abort_conn;
 
 out:
-	queue_delayed_work(system_wq, &fc->timeout.work,
+	queue_delayed_work(system_percpu_wq, &fc->timeout.work,
 			   fuse_timeout_timer_freq);
 	return;
 

fs/fuse/inode.c

···
 {
 	fc->timeout.req_timeout = secs_to_jiffies(timeout);
 	INIT_DELAYED_WORK(&fc->timeout.work, fuse_check_timeout);
-	queue_delayed_work(system_wq, &fc->timeout.work,
+	queue_delayed_work(system_percpu_wq, &fc->timeout.work,
 			   fuse_timeout_timer_freq);
 }
 

fs/nfs/namespace.c

···
 			num *= HZ;
 		*((int *)kp->arg) = num;
 		if (!list_empty(&nfs_automount_list))
-			mod_delayed_work(system_wq, &nfs_automount_task, num);
+			mod_delayed_work(system_percpu_wq, &nfs_automount_task, num);
 	} else {
 		*((int *)kp->arg) = -1*HZ;
 		cancel_delayed_work(&nfs_automount_task);

fs/nfs/nfs4renewd.c

···
 		timeout = 5 * HZ;
 	dprintk("%s: requeueing work. Lease period = %ld\n",
 			__func__, (timeout + HZ - 1) / HZ);
-	mod_delayed_work(system_wq, &clp->cl_renewd, timeout);
+	mod_delayed_work(system_percpu_wq, &clp->cl_renewd, timeout);
 	set_bit(NFS_CS_RENEWD, &clp->cl_res_state);
 	spin_unlock(&clp->cl_lock);
 }