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From:   "NeilBrown" <neilb@suse.de>
To:     "Jerry Zhang" <jerry@skydio.com>
Cc:     embedded@skydio.com, "Jerry Zhang" <Jerry@skydio.com>,
        "Chuck Lever" <chuck.lever@oracle.com>,
        "Jeff Layton" <jlayton@kernel.org>,
        "Trond Myklebust" <trond.myklebust@hammerspace.com>,
        "Anna Schumaker" <anna@kernel.org>,
        "J. Bruce Fields" <bfields@redhat.com>, linux-nfs@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] sunrpc: Fix incorrect parsing of expiry time
In-reply-to: <20230307220525.54895-1-Jerry@skydio.com>
References: <20230307220525.54895-1-Jerry@skydio.com>
Date:   Wed, 08 Mar 2023 09:30:59 +1100
Message-id: <167822825917.8008.11050193827453206272@noble.neil.brown.name>
Precedence: bulk

On Wed, 08 Mar 2023, Jerry Zhang wrote:
> The expiry time field is mean to be expressed in seconds since boot.

Correct.

> The get_expiry() function parses a relative time value in seconds.

Incorrect.  It parses and absoulte wall-clock time.

NeilBrown

> In order to get the absolute time of seconds since boot that the given
> message will expire, the right thing is to add seconds_since_boot()
> to the given relative value.
> 
> Previously this logic was subtracting boot.tv_sec from the relative
> value, which was causing some confusing behavior. The return type of
> time64_t could possibly underflow if time since boot is greater than
> the passed in relative argument. Also several checks in nfs code compare
> the return value to 0 to indicate failure, and this could spuriously
> be tripped if seconds since boot happened to match the argument.
> 
> Fixes: c5b29f885afe ("sunrpc: use seconds since boot in expiry cache")
> Signed-off-by: Jerry Zhang <Jerry@skydio.com>
> ---
>  include/linux/sunrpc/cache.h | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/include/linux/sunrpc/cache.h b/include/linux/sunrpc/cache.h
> index ec5a555df96f..b96b1319c93d 100644
> --- a/include/linux/sunrpc/cache.h
> +++ b/include/linux/sunrpc/cache.h
> @@ -301,16 +301,14 @@ static inline int get_time(char **bpp, time64_t *time)
>  }
>  
>  static inline time64_t get_expiry(char **bpp)
>  {
>  	time64_t rv;
> -	struct timespec64 boot;
>  
>  	if (get_time(bpp, &rv))
>  		return 0;
>  	if (rv < 0)
>  		return 0;
> -	getboottime64(&boot);
> -	return rv - boot.tv_sec;
> +	return rv + seconds_since_boot();
>  }
>  
>  #endif /*  _LINUX_SUNRPC_CACHE_H_ */
> -- 
> 2.37.3
> 
>