From 67c9e6270f3013e4d86ec57c4e7f27459f2a0652 Mon Sep 17 00:00:00 2001 From: "Ahmed S. Darwish" Date: Sat, 16 Oct 2021 10:49:07 +0200 Subject: net: sched: Protect Qdisc::bstats with u64_stats The not-per-CPU variant of qdisc tc (traffic control) statistics, Qdisc::gnet_stats_basic_packed bstats, is protected with Qdisc::running sequence counter. This sequence counter is used for reliably protecting bstats reads from parallel writes. Meanwhile, the seqcount's write section covers a much wider area than bstats update: qdisc_run_begin() => qdisc_run_end(). That read/write section asymmetry can lead to needless retries of the read section. To prepare for removing the Qdisc::running sequence counter altogether, introduce a u64_stats sync point inside bstats instead. Modify _bstats_update() to start/end the bstats u64_stats write section. For bisectability, and finer commits granularity, the bstats read section is still protected with a Qdisc::running read/retry loop and qdisc_run_begin/end() still starts/ends that seqcount write section. Once all call sites are modified to use _bstats_update(), the Qdisc::running seqcount will be removed and bstats read/retry loop will be modified to utilize the internal u64_stats sync point. Note, using u64_stats implies no sequence counter protection for 64-bit architectures. This can lead to the statistics "packets" vs. "bytes" values getting out of sync on rare occasions. The individual values will still be valid. [bigeasy: Minor commit message edits, init all gnet_stats_basic_packed.] Signed-off-by: Ahmed S. Darwish Signed-off-by: Sebastian Andrzej Siewior Signed-off-by: David S. Miller --- include/net/sch_generic.h | 2 ++ 1 file changed, 2 insertions(+) (limited to 'include/net/sch_generic.h') diff --git a/include/net/sch_generic.h b/include/net/sch_generic.h index 7bc2d30b5c06..d7746aea3cec 100644 --- a/include/net/sch_generic.h +++ b/include/net/sch_generic.h @@ -852,8 +852,10 @@ static inline int qdisc_enqueue(struct sk_buff *skb, struct Qdisc *sch, static inline void _bstats_update(struct gnet_stats_basic_packed *bstats, __u64 bytes, __u32 packets) { + u64_stats_update_begin(&bstats->syncp); bstats->bytes += bytes; bstats->packets += packets; + u64_stats_update_end(&bstats->syncp); } static inline void bstats_update(struct gnet_stats_basic_packed *bstats, -- cgit v1.2.3