Messages in this thread | | | Date | Wed, 12 May 2021 11:47:13 +0200 | From | "Ahmed S. Darwish" <> | Subject | Re: [PATCH] seqlock,lockdep: Only check for preemption_disabled in non-rt |
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On Fri, May 07, 2021, Davidlohr Bueso wrote: > This silences the writer hitting this nonsensical warning on PREEMPT_RT. > > Reported-by: Shung-Hsi Yu <shung-hsi.yu@suse.com> > Signed-off-by: Davidlohr Bueso <dbueso@suse.de> > --- > include/linux/seqlock.h | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/include/linux/seqlock.h b/include/linux/seqlock.h > index f61e34fbaaea..c8f9253f1a2f 100644 > --- a/include/linux/seqlock.h > +++ b/include/linux/seqlock.h > @@ -268,7 +268,9 @@ static inline bool __seqprop_preemptible(const seqcount_t *s) > > static inline void __seqprop_assert(const seqcount_t *s) > { > +#ifndef CONFIG_PREEMPT_RT > lockdep_assert_preemption_disabled(); > +#endif > } >
Nope, it is more complicated than that.
In general, for RT, seqcount_LOCKNAME_t variants should be used instead of plain seqcount_t, as they can be safely used while preemption is enabled on the write side.
For plain seqcount_t (which __seqprop_assert() is about), preemption must be disabled, even for PREEMPT_RT. So the patch above is invalid.
Now, there are still some call sites in the kernel which needs conversion obviously. I have a large patch series in queue which convert a number of remaining networking call sites (the changes are locking algorithm changes, not just direct substitution).
Good luck,
-- Ahmed S. Darwish Linutronix GmbH
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