Re: [PATCH v7] kcov: fix data corruption and race conditions on PREEMPT_RT

[Alexander Potapenko]

On Sat, Jul 25, 2026 at 11:59 PM Andrew Morton
<akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
>
> On Thu, 16 Jul 2026 08:01:29 +0900 Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx> 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?

Yeah, I think so.