linux-kernel - [PATCH 0/6] sched: TTWU, IPI, and assorted stuff

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Message-ID: <20200615125654.678940605@infradead.org>
Date:   Mon, 15 Jun 2020 14:56:54 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     mingo@...nel.org, tglx@...utronix.de
Cc:     linux-kernel@...r.kernel.org, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        paulmck@...nel.org, frederic@...nel.org, peterz@...radead.org
Subject: [PATCH 0/6] sched: TTWU, IPI, and assorted stuff

Hi,

So Paul reported rcutorture hitting a NULL dereference, and patch #1 fixes it.

Now, patch #1 is obviously correct, but I can't explain how exactly it leads to
the observed NULL pointer dereference. The NULL pointer deref happens in
find_matching_se()'s last while() loop when is_same_group() fails even though
both parents are NULL.

The only explanation I have for that is that we just did an activate_task()
while: 'task_cpu(p) != cpu_of(rq)', because then 'p->se.cfs_rq' doesn't match.
However, I can't see how the lack of #1 would lead to that. Never-the-less,
patch #2 adds assertions to warn us of this case.

Patch #3 is a trivial rename that ought to eradicate some confusion.

The last 3 patches is what I ended up with for cleaning up the whole
smp_call_function/irq_work/ttwu thing more.