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

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Message-ID: <20150617184245.GA9295@redhat.com>
Date:	Wed, 17 Jun 2015 20:42:45 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Jeff Moyer <jmoyer@...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()

On 06/17, Jeff Moyer wrote:
>
> 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.

Yes, agreed, will redo/resend tomorrow.

Thanks!

> -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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