linux-kernel - Re: [PATCH 2/3] tracing/user_events: Ensure bit is cleared on unregister

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Message-ID: <20230424213957.55c503c1@rorschach.local.home>
Date:   Mon, 24 Apr 2023 21:39:57 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Beau Belgrave <beaub@...ux.microsoft.com>
Cc:     mhiramat@...nel.org, mathieu.desnoyers@...icios.com,
        dcook@...ux.microsoft.com, alanau@...ux.microsoft.com,
        linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] tracing/user_events: Ensure bit is cleared on
 unregister

On Tue, 11 Apr 2023 14:17:08 -0700
Beau Belgrave <beaub@...ux.microsoft.com> wrote:

> +static int user_event_mm_clear_bit(struct user_event_mm *user_mm,
> +				   unsigned long uaddr, unsigned char bit)
> +{
> +	struct user_event_enabler enabler;
> +	int result;
> +
> +	memset(&enabler, 0, sizeof(enabler));
> +	enabler.addr = uaddr;
> +	enabler.values = bit;
> +retry:
> +	/* Prevents state changes from racing with new enablers */
> +	mutex_lock(&event_mutex);
> +
> +	/* Force the bit to be cleared, since no event is attached */
> +	mmap_read_lock(user_mm->mm);
> +	result = user_event_enabler_write(user_mm, &enabler, false);
> +	mmap_read_unlock(user_mm->mm);
> +
> +	mutex_unlock(&event_mutex);
> +
> +	if (result) {
> +		/* Attempt to fault-in and retry if it worked */
> +		if (!user_event_mm_fault_in(user_mm, uaddr))
> +			goto retry;

Without looking into the functions of this call, I wonder if this can
get into an infinite loop?

-- Steve


> +	}
> +
> +	return result;
> +}
> +