Merge branch 'remove-qdisc-running-counter'
Sebastian Andrzej Siewior says: ==================== Try to simplify the gnet_stats and remove qdisc->running sequence counter. The first few patches is a follow up to https://lore.kernel.org/all/20211007175000.2334713-1-bigeasy@linutronix.de/ The remaining patches (#5+) remove the seqcount_t (Qdisc::running) from the Qdisc. The statistics (Qdisc::bstats and Qdisc::cpu_bstats) use u64_stats_t and the "running state" is now represented by a bit in Qdisc::state. By removing the seqcount_t from Qdisc and decoupling the bstats statistics from the seqcount_t it is possible to query the statistics even if the Qdisc is running instead of waiting until it is idle again. The try-lock like usage of the seqcount_t in qdisc_run_begin() is problematic on PREEMPT_RT. Inside the qdisc_run_begin/end() qdisc->running sequence counter write sections, at sch_direct_xmit(), the seqcount write serialization lock is released then re-acquired. This is fine for !RT, because the writer is in a BH disabled region and there is a no in-IRQ reader. For RT though, BH sections are preemptible. The earlier introduced seqcount_LOCKNAME_t mechanism, which for RT the reader acquires then relesaes the write serailization lock to avoid infinite spinning if it preempts a seqcount write section, cannot work: the qdisc->running write serialization lock is already intermittingly released inside the seqcount write section. ==================== Signed-off-by: David S. Miller <davem@davemloft.net>
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