From: Andrew Morton <akpm@linux-foundation.org>
To: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: Alexander Potapenko <glider@google.com>,
Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
Dmitry Vyukov <dvyukov@google.com>,
kasan-dev <kasan-dev@googlegroups.com>,
LKML <linux-kernel@vger.kernel.org>,
Alan Stern <stern@rowland.harvard.edu>,
Andrey Konovalov <andreyknvl@gmail.com>,
Andrey Konovalov <andreyknvl@google.com>,
Clark Williams <williams@redhat.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Marco Elver <elver@google.com>,
Roman Gushchin <roman.gushchin@linux.dev>,
Christoph Hellwig <hch@infradead.org>,
Mark Brown <broonie@kernel.org>
Subject: Re: [PATCH v7] kcov: fix data corruption and race conditions on PREEMPT_RT
Date: Sat, 25 Jul 2026 14:59:36 -0700 [thread overview]
Message-ID: <20260725145936.11e2d08c90044b8bcb3ab149@linux-foundation.org> (raw)
In-Reply-To: <43552d09-2ce2-4b19-b0d3-a2d1ab952145@I-love.SAKURA.ne.jp>
On Thu, 16 Jul 2026 08:01:29 +0900 Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> wrote:
> syzbot is reporting KCOV state corruption on PREEMPT_RT kernels, for the
> temporary storage used for saving/restoring remote KCOV state is currently
> allocated as the per-CPU area.
>
> On PREEMPT_RT kernels, softirq handlers run as preemptible task threads
> (e.g., ksoftirqd). If a softirq context preempts a task running a remote
> KCOV session, it safely saves the task's state into the per-CPU area.
> However, if that softirq thread is subsequently preempted by a higher-
> priority softirq thread on the same CPU, the second softirq will overwrite
> the same per-CPU area, permanently destroying the original task's KCOV
> state.
>
> Fix this data corruption by moving the temporary storage from the per-CPU
> area to the per-thread area. Since each softirq thread now owns its own
> task context, nested softirq preemption no longer causes data overwrites.
All sounds rather unpleasant. Should we add cc:stable here?
next prev parent reply other threads:[~2026-07-25 21:59 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-05-04 15:30 [PATCH (draft)] kcov: fix potential kcov_mode corruption under CONFIG_PREEMPT_RT Tetsuo Handa
2026-05-04 15:39 ` Tetsuo Handa
2026-05-05 8:15 ` [PATCH] " Tetsuo Handa
2026-05-06 11:55 ` [PATCH v2] kcov: fix state corruption under CONFIG_PREEMPT_RT by eliminating per-cpu data Tetsuo Handa
2026-05-09 8:09 ` [PATCH v3] kcov: move kcov_remote_data to task_struct for RT and remove local_lock Tetsuo Handa
2026-05-15 7:10 ` Dmitry Vyukov
2026-05-20 10:33 ` Tetsuo Handa
2026-05-20 15:12 ` Sebastian Andrzej Siewior
2026-05-21 8:38 ` Sebastian Andrzej Siewior
2026-05-21 15:28 ` Tetsuo Handa
2026-05-21 18:14 ` Sebastian Andrzej Siewior
2026-05-22 2:39 ` Tetsuo Handa
2026-05-22 11:10 ` [PATCH v4] kcov: move kcov_remote_data to task_struct " Tetsuo Handa
2026-05-22 13:27 ` Sebastian Andrzej Siewior
2026-05-29 6:35 ` Tetsuo Handa
2026-06-27 9:58 ` [PATCH v5] kcov: fix data corruption and race conditions on PREEMPT_RT by moving saved remote state to task_struct Tetsuo Handa
2026-07-07 13:36 ` Tetsuo Handa
2026-07-07 15:00 ` Alexander Potapenko
2026-07-07 22:07 ` Tetsuo Handa
2026-07-08 15:28 ` Alexander Potapenko
2026-07-09 13:35 ` Tetsuo Handa
2026-07-10 10:43 ` Alexander Potapenko
2026-07-10 11:32 ` [PATCH v6] " Tetsuo Handa
2026-07-10 12:16 ` Alexander Potapenko
2026-07-15 23:01 ` [PATCH v7] kcov: fix data corruption and race conditions on PREEMPT_RT Tetsuo Handa
2026-07-16 9:12 ` Alexander Potapenko
2026-07-25 21:59 ` Andrew Morton [this message]
2026-07-27 10:37 ` Alexander Potapenko
2026-07-10 14:24 ` [PATCH v6] kcov: fix data corruption and race conditions on PREEMPT_RT by moving saved remote state to task_struct Sebastian Andrzej Siewior
2026-05-21 13:06 ` [PATCH v3] kcov: move kcov_remote_data to task_struct for RT and remove local_lock Alexander Potapenko
2026-05-21 14:39 ` Tetsuo Handa
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