linux-kernel - Question on commit dc7109aaa233 ("futex: Validate waiter correctly in futex_proxy_trylock

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Message-ID: <CAKXUXMzqmN1dYpbYSCXWN9VwHn8+MXj3P=G09qD6=atwrcJ8WA@mail.gmail.com>
Date:   Fri, 20 Aug 2021 13:17:42 +0200
From:   Lukas Bulwahn <lukas.bulwahn@...il.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Sudip Mukherjee <sudipm.mukherjee@...il.com>
Subject: Question on commit dc7109aaa233 ("futex: Validate waiter correctly in futex_proxy_trylock_atomic()")

Dear Thomas,

in commit dc7109aaa233 ("futex: Validate waiter correctly in
futex_proxy_trylock_atomic()") visible on next-20210819, you add:

+    /*
+     * Ensure that this is a waiter sitting in futex_wait_requeue_pi()
+     * and waiting on the 'waitqueue' futex which is always !PI.
+     */
+    if (!top_waiter->rt_waiter || top_waiter->pi_state)
+        ret = -EINVAL;

However, ret is unconditionally reassigned later and erases any
intended effect of this assignment. This is making that assignment
above a Dead Store, which clang-analyzer correctly warns about and
which motivates me to write you an email.

Did you intend to return -EINVAL here? So:

+       if (!top_waiter->rt_waiter || top_waiter->pi_state)
+               return -EINVAL;



Best regards,

Lukas

Static analysis tools are as foolish as they are... but every dog has its day...