linux-kernel - Re: [PATCH] aio: Fix return code of io

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Message-ID: <20141003181922.GZ17057@kvack.org>
Date:	Fri, 3 Oct 2014 14:19:22 -0400
From:	Benjamin LaHaise <bcrl@...ck.org>
To:	Kent Overstreet <kmo@...erainc.com>
Cc:	linux-kernel@...r.kernel.org, Zach Brown <zab@...bo.net>,
	Jeff Moyer <jmoyer@...hat.com>, Jens Axboe <axboe@...nel.dk>,
	Slava Pestov <sp@...erainc.com>
Subject: Re: [PATCH] aio: Fix return code of io_submit() (RFC)

Hi Kent,

On Fri, Oct 03, 2014 at 11:08:13AM -0700, Kent Overstreet wrote:
> io_submit() could return -EAGAIN on memory allocation failure when it should
> really have been returning -ENOMEM. This could confuse applications (i.e. fio)
> since -EAGAIN means "too many requests outstanding, wait until completions have
> been reaped" and if the application actually was tracking outstanding
> completions this wouldn't make a lot of sense.

Wouldn't it be simpler to just return an ERR_PTR with the appropriate 
return code rather than move all that code around?

		-ben

> NOTE:
> 
> the man page seems to imply that the current behaviour (-EAGAIN on allocation
> failure) has always been the case. I don't think it makes a lot of sense, but
> this should probably be discussed more widely in case applications have somehow
> come to rely on the current behaviour...
> 
> Signed-off-by: Kent Overstreet <kmo@...erainc.com>
> Cc: Benjamin LaHaise <bcrl@...ck.org>
> Cc: Zach Brown <zab@...bo.net>
> Cc: Jeff Moyer <jmoyer@...hat.com>
> Cc: Jens Axboe <axboe@...nel.dk>
> Cc: Slava Pestov <sp@...erainc.com>
> ---
>  fs/aio.c | 26 +++++++++++++-------------
>  1 file changed, 13 insertions(+), 13 deletions(-)
> 
> diff --git a/fs/aio.c b/fs/aio.c
> index 733750096b..556547044b 100644
> --- a/fs/aio.c
> +++ b/fs/aio.c
> @@ -933,23 +933,14 @@ static inline struct kiocb *aio_get_req(struct kioctx *ctx)
>  {
>  	struct kiocb *req;
>  
> -	if (!get_reqs_available(ctx)) {
> -		user_refill_reqs_available(ctx);
> -		if (!get_reqs_available(ctx))
> -			return NULL;
> -	}
> -
>  	req = kmem_cache_alloc(kiocb_cachep, GFP_KERNEL|__GFP_ZERO);
>  	if (unlikely(!req))
> -		goto out_put;
> +		return NULL;
>  
>  	percpu_ref_get(&ctx->reqs);
>  
>  	req->ki_ctx = ctx;
>  	return req;
> -out_put:
> -	put_reqs_available(ctx, 1);
> -	return NULL;
>  }
>  
>  static void kiocb_free(struct kiocb *req)
> @@ -1489,9 +1480,17 @@ static int io_submit_one(struct kioctx *ctx, struct iocb __user *user_iocb,
>  		return -EINVAL;
>  	}
>  
> +	if (!get_reqs_available(ctx)) {
> +		user_refill_reqs_available(ctx);
> +		if (!get_reqs_available(ctx))
> +			return -EAGAIN;
> +	}
> +
>  	req = aio_get_req(ctx);
> -	if (unlikely(!req))
> -		return -EAGAIN;
> +	if (unlikely(!req)) {
> +		ret = -ENOMEM;
> +		goto out_put;
> +	}
>  
>  	req->ki_filp = fget(iocb->aio_fildes);
>  	if (unlikely(!req->ki_filp)) {
> @@ -1533,9 +1532,10 @@ static int io_submit_one(struct kioctx *ctx, struct iocb __user *user_iocb,
>  
>  	return 0;
>  out_put_req:
> -	put_reqs_available(ctx, 1);
>  	percpu_ref_put(&ctx->reqs);
>  	kiocb_free(req);
> +out_put:
> +	put_reqs_available(ctx, 1);
>  	return ret;
>  }
>  
> -- 
> 2.1.1

-- 
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