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Message-ID: <fa113c5c-07c7-417b-8287-c9bf5f9b42a1@infradead.org>
Date: Mon, 4 Mar 2024 16:43:46 -0800
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Subject: Re: [PATCH] tracing: Have trace_marker writes be just half of
 TRACE_SEQ_SIZE
Content-Language: en-US
To: Steven Rostedt <rostedt@goodmis.org>, LKML
 <linux-kernel@vger.kernel.org>,
 Linux Trace Kernel <linux-trace-kernel@vger.kernel.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>,
 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
 Linus Torvalds <torvalds@linux-foundation.org>,
 Sachin Sant <sachinp@linux.ibm.com>
References: <20240304192710.4c99677c@gandalf.local.home>
From: Randy Dunlap <rdunlap@infradead.org>
In-Reply-To: <20240304192710.4c99677c@gandalf.local.home>
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> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index 8198bfc54b58..d68544aef65f 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -7320,6 +7320,17 @@ tracing_mark_write(struct file *filp, const char __user *ubuf,
>  	if ((ssize_t)cnt < 0)
>  		return -EINVAL;
>  
> +	/*
> +	 * TRACE_SEQ_SIZE is the total size of trace_seq buffer used
> +	 * for output. As the print event outputs more than just
> +	 * the string written, keep it smaller than the trace_seq
> +	 * as it could drop the event if the extra data makes it bigger
> +	 * than what the trace_seq can hold. Half he TRACE_SEQ_SIZE

	                                          the

> +	 * is more than enough.
> +	 */
> +	if (cnt > TRACE_SEQ_SIZE / 2)
> +		cnt = TRACE_SEQ_SIZE / 2;
> +
>  	meta_size = sizeof(*entry) + 2;  /* add '\0' and possible '\n' */
>   again:
>  	size = cnt + meta_size;


-- 
#Randy