linux-kernel - Re: [PATCH] ftrace: properly merge notrace hash

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Message-ID: <20250407160924.7c28fffd@gandalf.local.home>
Date: Mon, 7 Apr 2025 16:09:24 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Andy Chiu <andybnac@...il.com>
Cc: linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
 mark.rutland@....com, mhiramat@...nel.org, mathieu.desnoyers@...icios.com,
 bjorn@...osinc.com, puranjay12@...il.com, alexghiti@...osinc.com,
 paul.walmsley@...ive.com, greentime.hu@...ive.com, nick.hu@...ive.com,
 nylon.chen@...ive.com, eric.lin@...ive.com, vicent.chen@...ive.com,
 zong.li@...ive.com, yongxuan.wang@...ive.com, samuel.holland@...ive.com,
 olivia.chu@...ive.com, c2232430@...il.com
Subject: Re: [PATCH] ftrace: properly merge notrace hash

On Tue,  8 Apr 2025 02:07:44 +0800
Andy Chiu <andybnac@...il.com> wrote:

> The global notrace hash should be jointly decided by the intersection of
> each subops's notrace hash, but not the filter hash.
> 
> Fixes: 5fccc7552ccb ("ftrace: Add subops logic to allow one ops to manage many")
> Signed-off-by: Andy Chiu <andybnac@...il.com>
> ---
>  kernel/trace/ftrace.c | 11 +++++------
>  1 file changed, 5 insertions(+), 6 deletions(-)
> 
> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index 1a48aedb5255..ee662f380b61 100644
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -3526,18 +3526,17 @@ int ftrace_startup_subops(struct ftrace_ops *ops, struct ftrace_ops *subops, int
>  	    ftrace_hash_empty(subops->func_hash->notrace_hash)) {
>  		notrace_hash = EMPTY_HASH;
>  	} else {
> -		size_bits = max(ops->func_hash->filter_hash->size_bits,
> -				subops->func_hash->filter_hash->size_bits);
> +		size_bits = max(ops->func_hash->notrace_hash->size_bits,
> +				subops->func_hash->notrace_hash->size_bits);
>  		notrace_hash = alloc_ftrace_hash(size_bits);
>  		if (!notrace_hash) {
> -			free_ftrace_hash(filter_hash);
> +			free_ftrace_hash(notrace_hash);
>  			return -ENOMEM;
>  		}
>  
> -		ret = intersect_hash(&notrace_hash, ops->func_hash->filter_hash,
> -				     subops->func_hash->filter_hash);
> +		ret = intersect_hash(&notrace_hash, ops->func_hash->notrace_hash,
> +				     subops->func_hash->notrace_hash);

Thanks for catching this.


>  		if (ret < 0) {
> -			free_ftrace_hash(filter_hash);

The filter_hash still needs to be freed, as it could have been allocated in
the previous if statement and never used (both the filter_hash and
notrace_hash get used at the end of the function via ftrace_update_ops().

Care to send a v2?

-- Steve


>  			free_ftrace_hash(notrace_hash);
>  			return ret;
>  		}