linux-kernel - Re: [PATCH v3 1/2] livepatch: send a fake signal to all blocking tasks

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Date:   Thu, 2 Nov 2017 08:32:00 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Miroslav Benes <mbenes@...e.cz>
Cc:     jeyu@...nel.org, jikos@...nel.org, pmladek@...e.com,
        lpechacek@...e.cz, pavel@....cz, live-patching@...r.kernel.org,
        linux-kernel@...r.kernel.org, Oleg Nesterov <oleg@...hat.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andy Lutomirski <luto@...nel.org>,
        linuxppc-dev@...ts.ozlabs.org, x86@...nel.org
Subject: Re: [PATCH v3 1/2] livepatch: send a fake signal to all blocking
 tasks

On Tue, Oct 31, 2017 at 12:48:52PM +0100, Miroslav Benes wrote:
> diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
> index bf8c8fd72589..b7c60662baf3 100644
> --- a/kernel/livepatch/core.c
> +++ b/kernel/livepatch/core.c
> @@ -440,6 +440,7 @@ EXPORT_SYMBOL_GPL(klp_enable_patch);
>   * /sys/kernel/livepatch/<patch>
>   * /sys/kernel/livepatch/<patch>/enabled
>   * /sys/kernel/livepatch/<patch>/transition
> + * /sys/kernel/livepatch/<patch>/signal
>   * /sys/kernel/livepatch/<patch>/<object>
>   * /sys/kernel/livepatch/<patch>/<object>/<function,sympos>
>   */
> @@ -514,11 +515,37 @@ static ssize_t transition_show(struct kobject *kobj,
>  			patch == klp_transition_patch);
>  }
>  
> +static ssize_t signal_store(struct kobject *kobj, struct kobj_attribute *attr,
> +			    const char *buf, size_t count)
> +{
> +	int ret;
> +	bool val;
> +
> +	/*
> +	 * klp_mutex lock is not grabbed here intentionally. It is not really
> +	 * needed. The race window is harmless and grabbing the lock would only
> +	 * hold the action back.
> +	 */
> +	if (!klp_transition_patch)
> +		return -EINVAL;
> +
> +	ret = kstrtobool(buf, &val);
> +	if (ret)
> +		return ret;
> +
> +	if (val)
> +		klp_force_signals();
> +
> +	return count;
> +}

The function still has global functionality even though the sysfs entry
is now per-patch.  So if you do

  echo 1 > /sys/kernel/livepatch/patch1/signal

But patch2 is in transition, then it will send signals based on patch2.
Instead it should probably return an error.

There's a similar issue with force_store().

-- 
Josh