linux-kernel - Re: [PATCH v2] livepatch: add locking to force and signal functions

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Message-ID: <20180111150915.k3smqm3j6bfesup3@treble>
Date:   Thu, 11 Jan 2018 09:09:15 -0600
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Miroslav Benes <mbenes@...e.cz>
Cc:     jeyu@...nel.org, jikos@...nel.org, pmladek@...e.com,
        jbaron@...mai.com, live-patching@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] livepatch: add locking to force and signal functions

On Thu, Dec 21, 2017 at 02:40:43PM +0100, Miroslav Benes wrote:
> klp_send_signals() and klp_force_transition() do not acquire klp_mutex,
> because it seemed to be superfluous. A potential race in
> klp_send_signals() was harmless and there was nothing in
> klp_force_transition() which needed to be synchronized. That changed
> with the addition of klp_forced variable during the review process.
> 
> There is a small window now, when klp_complete_transition() does not see
> klp_forced set to true while all tasks have been already transitioned to
> the target state. module_put() is called and the module can be removed.
> 
> Acquire klp_mutex in sysfs callback to prevent it. Do the same for the
> signal sending just to be sure. There is no real downside to that.
> 
> Reported-by: Jason Baron <jbaron@...mai.com>
> Signed-off-by: Miroslav Benes <mbenes@...e.cz>

Acked-by: Josh Poimboeuf <jpoimboe@...hat.com>

-- 
Josh