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Date: Thu, 12 Apr 2012 16:09:12 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: handai.szj@gmail.com
Cc: linux-kernel@vger.kernel.org, davidel@xmailserver.org,
        Sha Zhengju <handai.szj@taobao.com>
Subject: Re: [PATCH] eventfd: change int to __u64 in eventfd_signal()
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On Thu, 12 Apr 2012 18:01:20 +0800
handai.szj@gmail.com wrote:

> From: Sha Zhengju <handai.szj@taobao.com>
> 
> From: Sha Zhengju <handai.szj@taobao.com>
> 
> eventfd_ctx->count is an __u64 counter which is allowed to reach ULLONG_MAX.
> Now eventfd_write() add an __u64 value to "count", but kernel side 
> eventfd_signal() only add an int value to it. So make them consistent here.  
> 
> ...
>
> --- a/fs/eventfd.c
> +++ b/fs/eventfd.c
> @@ -51,7 +51,7 @@ struct eventfd_ctx {
>   *
>   * -EINVAL    : The value of @n is negative.
>   */
> -int eventfd_signal(struct eventfd_ctx *ctx, int n)
> +__u64 eventfd_signal(struct eventfd_ctx *ctx, __u64 n)
>  {
>  	unsigned long flags;
>  
> @@ -59,7 +59,7 @@ int eventfd_signal(struct eventfd_ctx *ctx, int n)
>  		return -EINVAL;
>  	spin_lock_irqsave(&ctx->wqh.lock, flags);
>  	if (ULLONG_MAX - ctx->count < n)
> -		n = (int) (ULLONG_MAX - ctx->count);
> +		n = ULLONG_MAX - ctx->count;
>  	ctx->count += n;
>  	if (waitqueue_active(&ctx->wqh))
>  		wake_up_locked_poll(&ctx->wqh, POLLIN);

Changing `n' to an unsigned type makes the "if (n < 0)" test a no-op.

Every in-kernel caller of eventfd_signal() passes n=1.  All of them. 
Perhaps we can just remove that argument and hard-wire the +1
assumption into eventfd_signal().