[PATCH] stop elv_unregister() from rogering other iosched's data, fix locking

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

block/as-iosched.c

@@ -195,6 +195,12 @@ static void free_as_io_context(struct as_io_context *aic)
 	kfree(aic);
 }
 
+static void as_trim(struct io_context *ioc)
+{
+	kfree(ioc->aic);
+	ioc->aic = NULL;
+}
+
 /* Called when the task exits */
 static void exit_as_io_context(struct as_io_context *aic)
 {
@@ -1860,6 +1866,7 @@ static struct elevator_type iosched_as = {
 		.elevator_may_queue_fn =	as_may_queue,
 		.elevator_init_fn =		as_init_queue,
 		.elevator_exit_fn =		as_exit_queue,
+		.trim =				as_trim,
 	},
 
 	.elevator_ktype = &as_ktype,

block/cfq-iosched.c

@@ -1211,6 +1211,13 @@ static void cfq_free_io_context(struct cfq_io_context *cic)
 	kmem_cache_free(cfq_ioc_pool, cic);
 }
 
+static void cfq_trim(struct io_context *ioc)
+{
+	ioc->set_ioprio = NULL;
+	if (ioc->cic)
+		cfq_free_io_context(ioc->cic);
+}
+
 /*
  * Called with interrupts disabled
  */
@@ -2472,6 +2479,7 @@ static struct elevator_type iosched_cfq = {
 		.elevator_may_queue_fn =	cfq_may_queue,
 		.elevator_init_fn =		cfq_init_queue,
 		.elevator_exit_fn =		cfq_exit_queue,
+		.trim =				cfq_trim,
 	},
 	.elevator_ktype =	&cfq_ktype,
 	.elevator_name =	"cfq",

block/elevator.c

@@ -675,21 +675,15 @@ void elv_unregister(struct elevator_type *e)
 	/*
 	 * Iterate every thread in the process to remove the io contexts.
 	 */
+	if (e->ops.trim) {
 		read_lock(&tasklist_lock);
 		do_each_thread(g, p) {
-		struct io_context *ioc = p->io_context;
-		if (ioc && ioc->cic) {
-			ioc->cic->exit(ioc->cic);
-			ioc->cic->dtor(ioc->cic);
-			ioc->cic = NULL;
-		}
-		if (ioc && ioc->aic) {
-			ioc->aic->exit(ioc->aic);
-			ioc->aic->dtor(ioc->aic);
-			ioc->aic = NULL;
-		}
+			task_lock(p);
+			e->ops.trim(p->io_context);
+			task_unlock(p);
 		} while_each_thread(g, p);
 		read_unlock(&tasklist_lock);
+	}
 
 	spin_lock_irq(&elv_list_lock);
 	list_del_init(&e->list);

include/linux/elevator.h

@@ -48,6 +48,7 @@ struct elevator_ops
 
 	elevator_init_fn *elevator_init_fn;
 	elevator_exit_fn *elevator_exit_fn;
+	void (*trim)(struct io_context *);
 };
 
 #define ELV_NAME_MAX	(16)