From 3ffa3c0e3f6e62f67fc2346ca60161dfb030083d Mon Sep 17 00:00:00 2001
From: Al Viro <viro@zeniv.linux.org.uk>
Date: Sun, 24 Jun 2012 10:00:10 +0400
Subject: [PATCH] aio: now fput() is OK from interrupt context; get rid of
 manual delayed __fput()

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
 fs/aio.c | 73 +++-----------------------------------------------------
 1 file changed, 3 insertions(+), 70 deletions(-)

diff --git a/fs/aio.c b/fs/aio.c
index 55c4c765605..71f613cf4a8 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -56,13 +56,6 @@ static struct kmem_cache	*kioctx_cachep;
 
 static struct workqueue_struct *aio_wq;
 
-/* Used for rare fput completion. */
-static void aio_fput_routine(struct work_struct *);
-static DECLARE_WORK(fput_work, aio_fput_routine);
-
-static DEFINE_SPINLOCK(fput_lock);
-static LIST_HEAD(fput_head);
-
 static void aio_kick_handler(struct work_struct *);
 static void aio_queue_work(struct kioctx *);
 
@@ -479,7 +472,6 @@ static int kiocb_batch_refill(struct kioctx *ctx, struct kiocb_batch *batch)
 {
 	unsigned short allocated, to_alloc;
 	long avail;
-	bool called_fput = false;
 	struct kiocb *req, *n;
 	struct aio_ring *ring;
 
@@ -495,28 +487,11 @@ static int kiocb_batch_refill(struct kioctx *ctx, struct kiocb_batch *batch)
 	if (allocated == 0)
 		goto out;
 
-retry:
 	spin_lock_irq(&ctx->ctx_lock);
 	ring = kmap_atomic(ctx->ring_info.ring_pages[0]);
 
 	avail = aio_ring_avail(&ctx->ring_info, ring) - ctx->reqs_active;
 	BUG_ON(avail < 0);
-	if (avail == 0 && !called_fput) {
-		/*
-		 * Handle a potential starvation case.  It is possible that
-		 * we hold the last reference on a struct file, causing us
-		 * to delay the final fput to non-irq context.  In this case,
-		 * ctx->reqs_active is artificially high.  Calling the fput
-		 * routine here may free up a slot in the event completion
-		 * ring, allowing this allocation to succeed.
-		 */
-		kunmap_atomic(ring);
-		spin_unlock_irq(&ctx->ctx_lock);
-		aio_fput_routine(NULL);
-		called_fput = true;
-		goto retry;
-	}
-
 	if (avail < allocated) {
 		/* Trim back the number of requests. */
 		list_for_each_entry_safe(req, n, &batch->head, ki_batch) {
@@ -570,36 +545,6 @@ static inline void really_put_req(struct kioctx *ctx, struct kiocb *req)
 		wake_up_all(&ctx->wait);
 }
 
-static void aio_fput_routine(struct work_struct *data)
-{
-	spin_lock_irq(&fput_lock);
-	while (likely(!list_empty(&fput_head))) {
-		struct kiocb *req = list_kiocb(fput_head.next);
-		struct kioctx *ctx = req->ki_ctx;
-
-		list_del(&req->ki_list);
-		spin_unlock_irq(&fput_lock);
-
-		/* Complete the fput(s) */
-		if (req->ki_filp != NULL)
-			fput(req->ki_filp);
-
-		/* Link the iocb into the context's free list */
-		rcu_read_lock();
-		spin_lock_irq(&ctx->ctx_lock);
-		really_put_req(ctx, req);
-		/*
-		 * at that point ctx might've been killed, but actual
-		 * freeing is RCU'd
-		 */
-		spin_unlock_irq(&ctx->ctx_lock);
-		rcu_read_unlock();
-
-		spin_lock_irq(&fput_lock);
-	}
-	spin_unlock_irq(&fput_lock);
-}
-
 /* __aio_put_req
  *	Returns true if this put was the last user of the request.
  */
@@ -618,21 +563,9 @@ static int __aio_put_req(struct kioctx *ctx, struct kiocb *req)
 	req->ki_cancel = NULL;
 	req->ki_retry = NULL;
 
-	/*
-	 * Try to optimize the aio and eventfd file* puts, by avoiding to
-	 * schedule work in case it is not final fput() time. In normal cases,
-	 * we would not be holding the last reference to the file*, so
-	 * this function will be executed w/out any aio kthread wakeup.
-	 */
-	if (unlikely(!fput_atomic(req->ki_filp))) {
-		spin_lock(&fput_lock);
-		list_add(&req->ki_list, &fput_head);
-		spin_unlock(&fput_lock);
-		schedule_work(&fput_work);
-	} else {
-		req->ki_filp = NULL;
-		really_put_req(ctx, req);
-	}
+	fput(req->ki_filp);
+	req->ki_filp = NULL;
+	really_put_req(ctx, req);
 	return 1;
 }