fs/aio: simple simple work

|BUG: sleeping function called from invalid context at kernel/locking/rtmutex.c:768
|in_atomic(): 1, irqs_disabled(): 0, pid: 26, name: rcuos/2
|2 locks held by rcuos/2/26:
| #0:  (rcu_callback){.+.+..}, at: [<ffffffff810b1a12>] rcu_nocb_kthread+0x1e2/0x380
| #1:  (rcu_read_lock_sched){.+.+..}, at: [<ffffffff812acd26>] percpu_ref_kill_rcu+0xa6/0x1c0
|Preemption disabled at:[<ffffffff810b1a93>] rcu_nocb_kthread+0x263/0x380
|Call Trace:
| [<ffffffff81582e9e>] dump_stack+0x4e/0x9c
| [<ffffffff81077aeb>] __might_sleep+0xfb/0x170
| [<ffffffff81589304>] rt_spin_lock+0x24/0x70
| [<ffffffff811c5790>] free_ioctx_users+0x30/0x130
| [<ffffffff812ace34>] percpu_ref_kill_rcu+0x1b4/0x1c0
| [<ffffffff810b1a93>] rcu_nocb_kthread+0x263/0x380
| [<ffffffff8106e046>] kthread+0xd6/0xf0
| [<ffffffff81591eec>] ret_from_fork+0x7c/0xb0

replace this preempt_disable() friendly swork.

Reported-By: Mike Galbraith <umgwanakikbuti@gmail.com>
Suggested-by: Benjamin LaHaise <bcrl@kvack.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

fs/aio.c

@@ -40,6 +40,7 @@
 #include <linux/ramfs.h>
 #include <linux/percpu-refcount.h>
 #include <linux/mount.h>
+#include <linux/swork.h>
 
 #include <asm/kmap_types.h>
 #include <linux/uaccess.h>
@@ -115,7 +116,7 @@ struct kioctx {
 	struct page		**ring_pages;
 	long			nr_pages;
 
-	struct work_struct	free_work;
+	struct swork_event	free_work;
 
 	/*
 	 * signals when all in-flight requests are done
@@ -258,6 +259,7 @@ static int __init aio_setup(void)
 		.mount		= aio_mount,
 		.kill_sb	= kill_anon_super,
 	};
+	BUG_ON(swork_get());
 	aio_mnt = kern_mount(&aio_fs);
 	if (IS_ERR(aio_mnt))
 		panic("Failed to create aio fs mount.");
@@ -588,9 +590,9 @@ static int kiocb_cancel(struct aio_kiocb *kiocb)
 	return cancel(&kiocb->common);
 }
 
-static void free_ioctx(struct work_struct *work)
+static void free_ioctx(struct swork_event *sev)
 {
-	struct kioctx *ctx = container_of(work, struct kioctx, free_work);
+	struct kioctx *ctx = container_of(sev, struct kioctx, free_work);
 
 	pr_debug("freeing %p\n", ctx);
 
@@ -609,18 +611,18 @@ static void free_ioctx_reqs(struct percpu_ref *ref)
 	if (ctx->rq_wait && atomic_dec_and_test(&ctx->rq_wait->count))
 		complete(&ctx->rq_wait->comp);
 
-	INIT_WORK(&ctx->free_work, free_ioctx);
-	schedule_work(&ctx->free_work);
+	INIT_SWORK(&ctx->free_work, free_ioctx);
+	swork_queue(&ctx->free_work);
 }
 
 /*
  * When this function runs, the kioctx has been removed from the "hash table"
  * and ctx->users has dropped to 0, so we know no more kiocbs can be submitted -
  * now it's safe to cancel any that need to be.
  */
-static void free_ioctx_users(struct percpu_ref *ref)
+static void free_ioctx_users_work(struct swork_event *sev)
 {
-	struct kioctx *ctx = container_of(ref, struct kioctx, users);
+	struct kioctx *ctx = container_of(sev, struct kioctx, free_work);
 	struct aio_kiocb *req;
 
 	spin_lock_irq(&ctx->ctx_lock);
@@ -639,6 +641,14 @@ static void free_ioctx_users(struct percpu_ref *ref)
 	percpu_ref_put(&ctx->reqs);
 }
 
+static void free_ioctx_users(struct percpu_ref *ref)
+{
+	struct kioctx *ctx = container_of(ref, struct kioctx, users);
+
+	INIT_SWORK(&ctx->free_work, free_ioctx_users_work);
+	swork_queue(&ctx->free_work);
+}
+
 static int ioctx_add_table(struct kioctx *ctx, struct mm_struct *mm)
 {
 	unsigned i, new_nr;