linux-kernel - [PATCH v2 2/3] aio: make aio

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Date:	Wed, 17 Jun 2015 01:50:06 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Al Viro <viro@...IV.linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Benjamin LaHaise <bcrl@...ck.org>,
	Jeff Moyer <jmoyer@...hat.com>
Cc:	linux-aio@...ck.org, linux-kernel@...r.kernel.org
Subject: [PATCH v2 2/3] aio: make aio_ring->dead boolean

On 06/17, Oleg Nesterov wrote:
>
> @@ -327,7 +327,7 @@ static int aio_ring_remap(struct file *file, struct vm_area_struct *vma)
>  	for (i = 0; i < table->nr; i++) {
>  		struct kioctx *ctx = table->table[i];
>
> -		if (!ctx || WARN_ON(atomic_read(&ctx->dead)))
> +		if (!ctx || ctx->dead)

Argh, sorry, I removed WARN_ON() by accident.

------------------------------------------------------------------------------
Subject: [PATCH v2 2/3] aio: make aio_ring->dead boolean

"atomic_t dead" makes no sense. atomic_read() is the plain LOAD,
it doesn't have some "additional" synchronization with xchg().

And now that kill_ioctx() sets "dead" under mm->ioctx_lock we do
not even need xchg().

Signed-off-by: Oleg Nesterov <oleg@...hat.com>
---
 fs/aio.c |   11 ++++++-----
 1 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/fs/aio.c b/fs/aio.c
index 0693333..b22c20a 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -84,7 +84,7 @@ struct ctx_rq_wait {
 
 struct kioctx {
 	struct percpu_ref	users;
-	atomic_t		dead;
+	bool			dead;
 
 	struct percpu_ref	reqs;
 
@@ -327,7 +327,7 @@ static int aio_ring_remap(struct file *file, struct vm_area_struct *vma)
 	for (i = 0; i < table->nr; i++) {
 		struct kioctx *ctx = table->table[i];
 
-		if (!ctx || WARN_ON(atomic_read(&ctx->dead)))
+		if (!ctx || WARN_ON(ctx->dead))
 			continue;
 
 		if (ctx->aio_ring_file == file) {
@@ -768,7 +768,7 @@ static struct kioctx *ioctx_alloc(unsigned nr_events)
 err_cleanup:
 	aio_nr_sub(ctx->max_reqs);
 err_ctx:
-	atomic_set(&ctx->dead, 1);
+	ctx->dead = true; /* unneeded */
 	if (ctx->mmap_size)
 		vm_munmap(ctx->mmap_base, ctx->mmap_size);
 	aio_free_ring(ctx);
@@ -793,11 +793,12 @@ static int kill_ioctx(struct mm_struct *mm, struct kioctx *ctx,
 	struct kioctx_table *table;
 
 	spin_lock(&mm->ioctx_lock);
-	if (atomic_xchg(&ctx->dead, 1)) {
+	if (unlikely(ctx->dead)) {
 		spin_unlock(&mm->ioctx_lock);
 		return -EINVAL;
 	}
 
+	ctx->dead = true;
 	table = rcu_dereference_raw(mm->ioctx_table);
 	WARN_ON(ctx != table->table[ctx->id]);
 	table->table[ctx->id] = NULL;
@@ -1239,7 +1240,7 @@ static bool aio_read_events(struct kioctx *ctx, long min_nr, long nr,
 	if (ret > 0)
 		*i += ret;
 
-	if (unlikely(atomic_read(&ctx->dead)))
+	if (unlikely(ctx->dead))
 		ret = -EINVAL;
 
 	if (!*i)
-- 
1.5.5.1


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