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Tue, 11 Aug 2026 06:43:03 -0700 (PDT) Date: Tue, 11 Aug 2026 06:43:03 -0700 In-Reply-To: <696689a1.a70a0220.2cc00b.0001.GAE@google.com> X-Google-Appengine-App-Id: s~syzkaller X-Google-Appengine-App-Id-Alias: syzkaller Message-ID: <6a7b26e7.9c11d2ce.289b96.0107.GAE@google.com> Subject: Forwarded: [syz test] net/sched: taprio: reject too-small software schedule intervals From: syzbot To: linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com Content-Type: text/plain; charset="UTF-8" For archival purposes, forwarding an incoming command email to linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com. *** Subject: [syz test] net/sched: taprio: reject too-small software schedule intervals Author: junjie.cao@linux.dev #syz test: git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net.git dd057113ac7ba5bdd2aed3d9405305911152f911 Signed-off-by: Junjie Cao diff --git a/net/sched/sch_taprio.c b/net/sched/sch_taprio.c index 299234a5f0fe..f740918a3b17 100644 --- a/net/sched/sch_taprio.c +++ b/net/sched/sch_taprio.c @@ -259,6 +259,27 @@ static int length_to_duration(struct taprio_sched *q, int len) return div_u64(len * atomic64_read(&q->picos_per_byte), PSEC_PER_NSEC); } +/* Software schedules service one hrtimer expiry per entry; an interval + * shorter than the expiry servicing cost rearms the timer in the past + * and storms the CPU. 100us stays above that cost across configurations + * (sub-us with lockdep, more under KASAN) and below any practical + * schedule. + */ +#define TAPRIO_MIN_SW_INTERVAL_NS (100 * NSEC_PER_USEC) + +static s64 taprio_min_interval(struct taprio_sched *q) +{ + s64 min_interval = length_to_duration(q, ETH_ZLEN); + + /* Only pure software schedules arm the per-entry hrtimer. */ + if (!FULL_OFFLOAD_IS_ENABLED(q->flags) && + !TXTIME_ASSIST_IS_ENABLED(q->flags)) + min_interval = max_t(s64, min_interval, + TAPRIO_MIN_SW_INTERVAL_NS); + + return min_interval; +} + static int duration_to_length(struct taprio_sched *q, u64 duration) { return div_u64(duration * PSEC_PER_NSEC, atomic64_read(&q->picos_per_byte)); @@ -1038,7 +1059,7 @@ static int fill_sched_entry(struct taprio_sched *q, struct nlattr **tb, struct sched_entry *entry, struct netlink_ext_ack *extack) { - int min_duration = length_to_duration(q, ETH_ZLEN); + s64 min_duration = taprio_min_interval(q); u32 interval = 0; if (tb[TCA_TAPRIO_SCHED_ENTRY_CMD]) @@ -1166,7 +1187,7 @@ static int parse_taprio_schedule(struct taprio_sched *q, struct nlattr **tb, new->cycle_time = cycle; } - if (new->cycle_time < new->num_entries * length_to_duration(q, ETH_ZLEN)) { + if (new->cycle_time < (s64)new->num_entries * taprio_min_interval(q)) { NL_SET_ERR_MSG(extack, "'cycle_time' is too small"); return -EINVAL; }