linux-kernel - Re: [PATCH 1/3] aio_ring_remap: turn the ctx->dead check into WARN

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Message-ID: <x49pp4uns04.fsf@segfault.boston.devel.redhat.com>
Date:	Wed, 17 Jun 2015 13:50:51 -0400
From:	Jeff Moyer <jmoyer@...hat.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Al Viro <viro@...IV.linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Benjamin LaHaise <bcrl@...ck.org>, linux-aio@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] aio_ring_remap: turn the ctx->dead check into WARN_ON()

Oleg Nesterov <oleg@...hat.com> writes:

> atomic_read(&ctx->dead) in aio_ring_remap() looks confusing.
> kill_ioctx() sets ctx->dead and removes ctx from ->ioctx_table
> "atomically" under mm->ioctx_lock, so aio_ring_remap() can never
> see a dead ctx.
>
> If we really want this check, we should put it under WARN_ON()
> and it should not depend on aio_ring_file == file.

Just get rid of the check, it doesn't make any sense.

-Jeff

>
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>
> ---
>  fs/aio.c |   16 ++++++++--------
>  1 files changed, 8 insertions(+), 8 deletions(-)
>
> diff --git a/fs/aio.c b/fs/aio.c
> index 480440f..0693333 100644
> --- a/fs/aio.c
> +++ b/fs/aio.c
> @@ -325,14 +325,14 @@ static int aio_ring_remap(struct file *file, struct vm_area_struct *vma)
>  	rcu_read_lock();
>  	table = rcu_dereference(mm->ioctx_table);
>  	for (i = 0; i < table->nr; i++) {
> -		struct kioctx *ctx;
> -
> -		ctx = table->table[i];
> -		if (ctx && ctx->aio_ring_file == file) {
> -			if (!atomic_read(&ctx->dead)) {
> -				ctx->user_id = ctx->mmap_base = vma->vm_start;
> -				res = 0;
> -			}
> +		struct kioctx *ctx = table->table[i];
> +
> +		if (!ctx || WARN_ON(atomic_read(&ctx->dead)))
> +			continue;
> +
> +		if (ctx->aio_ring_file == file) {
> +			ctx->user_id = ctx->mmap_base = vma->vm_start;
> +			res = 0;
>  			break;
>  		}
>  	}
--
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