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

From: Oleg Nesterov
Date: Tue Jun 16 2015 - 19:51:24 EST


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@xxxxxxxxxx>
---
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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