On Tue, Feb 23, 2021 at 02:53:40PM +0100, Juri Lelli wrote:

On 23/02/21 12:00, Sebastian Andrzej Siewior wrote:

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On 2021-02-23 11:49:07 [+0100], Juri Lelli wrote:

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Hi,

Hi,

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I'm seeing the following splat right after boot (or during late boot
phases) with v5.11-rt7 (LOCKDEP enabled).

…

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[   85.273588] WARNING: CPU: 5 PID: 1416 at include/linux/seqlock.h:271 nft_counter_eval+0x95/0x130 [nft_counter]

…

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[   85.273713] RIP: 0010:nft_counter_eval+0x95/0x130 [nft_counter]

This is a per-CPU seqcount_t in net/netfilter/nft_counter.c which is
only protected by local_bh_disabled(). The warning expects preemption
to be disabled which is the case on !RT but not on RT.

Not sure what to do about this. It is doing anything wrong as of now. It
is noisy.

So, I'm a bit confused and I'm very likely missing details (still
digesting the seqprop_ magic), but write_seqcount_being() has

 if (seqprop_preemptible(s))
     preempt_disable();

which in this case (no lock associated) is defined to return false,

Preemption is disabled if and only if:

  1. It's a CONFIG_PREEMPT_RT=n system
  2. There's a lock associated with the sequence counter
  3. That lock is also preemptible (e.g., a mutex)

In your case, the 3 condititions are OFF. You're on a PREEMPT_RT=y
kernel and the sequence counter in question has no lock associated.

As Sebastian summarized, the error is just "noisy" at this point.

We will of course need to find a (mainline-friendly) way to let the
lockdep splat go away for -rt kernels. But for now, it's not harmful.

Good luck,

--
Ahmed S. Darwish