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    SubjectRe: [RT v5.11-rt7] WARNING at include/linux/seqlock.h:271 nft_counter_eval
    On Tue, Feb 23, 2021 at 02:53:40PM +0100, Juri Lelli wrote:
    > On 23/02/21 12:00, Sebastian Andrzej Siewior wrote:
    > > On 2021-02-23 11:49:07 [+0100], Juri Lelli wrote:
    > > > Hi,
    > > Hi,
    > >
    > > > I'm seeing the following splat right after boot (or during late boot
    > > > phases) with v5.11-rt7 (LOCKDEP enabled).
    > > …
    > > > [ 85.273588] WARNING: CPU: 5 PID: 1416 at include/linux/seqlock.h:271 nft_counter_eval+0x95/0x130 [nft_counter]
    > > …
    > > > [ 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

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