On Fri, Sep 15, 2023 at 11:45:02AM +0200, Ingo Molnar wrote:
>
> * tip-bot2 for Lukas Wunner <tip-bot2@xxxxxxxxxxxxx> wrote:
>
> > The following commit has been merged into the core/urgent branch of tip:
> >
> > Commit-ID: cccd32816506cbac3a4c65d9dff51b3125ef1a03
> > Gitweb: https://git.kernel.org/tip/cccd32816506cbac3a4c65d9dff51b3125ef1a03
> > Author: Lukas Wunner <lukas@xxxxxxxxx>
> > AuthorDate: Fri, 15 Sep 2023 09:55:39 +02:00
> > Committer: Ingo Molnar <mingo@xxxxxxxxxx>
> > CommitterDate: Fri, 15 Sep 2023 11:28:08 +02:00
> >
> > panic: Reenable preemption in WARN slowpath
> >
> > Commit:
> >
> > 5a5d7e9badd2 ("cpuidle: lib/bug: Disable rcu_is_watching() during WARN/BUG")
> >
> > amended warn_slowpath_fmt() to disable preemption until the WARN splat
> > has been emitted.
> >
> > However the commit neglected to reenable preemption in the !fmt codepath,
> > i.e. when a WARN splat is emitted without additional format string.
> >
> > One consequence is that users may see more splats than intended. E.g. a
> > WARN splat emitted in a work item results in at least two extra splats:
> >
> > BUG: workqueue leaked lock or atomic
> > (emitted by process_one_work())
> >
> > BUG: scheduling while atomic
> > (emitted by worker_thread() -> schedule())
> >
> > Ironically the point of the commit was to *avoid* extra splats. ;)
> >
> > Fix it.
>
> > diff --git a/kernel/panic.c b/kernel/panic.c
> > index 07239d4..ffa037f 100644
> > --- a/kernel/panic.c
> > +++ b/kernel/panic.c
> > @@ -697,6 +697,7 @@ void warn_slowpath_fmt(const char *file, int line, unsigned taint,
> > if (!fmt) {
> > __warn(file, line, __builtin_return_address(0), taint,
> > NULL, NULL);
> > + warn_rcu_exit(rcu);
> > return;
>
> BTW., one more thing we might want to consider here is to re-enable
> preemption in warn_rcu_exit() a bit more gently, without forcing a
> pending reschedule, ie. preempt_enable_no_resched() or so?
nah, it's a warn, if that triggers you get to keep the pieces. Also
preempt_enable_no_resched() isn't exported because its a horribly
dangerous function.
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