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[212.8.243.115]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-493ccdb566csm55475105e9.7.2026.07.03.08.33.14 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 03 Jul 2026 08:33:15 -0700 (PDT) Message-ID: <9510a0f557a029883e1e28681e2a80543099172a.camel@redhat.com> Subject: Re: [PATCH v3] sched: set TIF_NEED_RESCHED before calling __trace_set_need_resched() From: Gabriele Monaco To: Sechang Lim , Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot Cc: Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Valentin Schneider , K Prateek Nayak , linux-kernel@vger.kernel.org Date: Fri, 03 Jul 2026 17:33:13 +0200 In-Reply-To: <20260630084750.2792851-1-rhkrqnwk98@gmail.com> References: <20260630084750.2792851-1-rhkrqnwk98@gmail.com> Autocrypt: addr=gmonaco@redhat.com; prefer-encrypt=mutual; keydata=mDMEZuK5YxYJKwYBBAHaRw8BAQdAmJ3dM9Sz6/Hodu33Qrf8QH2bNeNbOikqYtxWFLVm0 1a0JEdhYnJpZWxlIE1vbmFjbyA8Z21vbmFjb0BrZXJuZWwub3JnPoiZBBMWCgBBFiEEysoR+AuB3R Zwp6j270psSVh4TfIFAmjKX2MCGwMFCQWjmoAFCwkIBwICIgIGFQoJCAsCBBYCAwECHgcCF4AACgk Q70psSVh4TfIQuAD+JulczTN6l7oJjyroySU55Fbjdvo52xiYYlMjPG7dCTsBAMFI7dSL5zg98I+8 cXY1J7kyNsY6/dcipqBM4RMaxXsOtCRHYWJyaWVsZSBNb25hY28gPGdtb25hY29AcmVkaGF0LmNvb T6InAQTFgoARAIbAwUJBaOagAULCQgHAgIiAgYVCgkICwIEFgIDAQIeBwIXgBYhBMrKEfgLgd0WcK eo9u9KbElYeE3yBQJoymCyAhkBAAoJEO9KbElYeE3yjX4BAJ/ETNnlHn8OjZPT77xGmal9kbT1bC1 7DfrYVISWV2Y1AP9HdAMhWNAvtCtN2S1beYjNybuK6IzWYcFfeOV+OBWRDQ== Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.60.2 (3.60.2-1.fc44) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Tue, 2026-06-30 at 08:47 +0000, Sechang Lim wrote: > set_tsk_need_resched() tests TIF_NEED_RESCHED, calls > __trace_set_need_resched() if the flag is clear, then sets it via > set_tsk_thread_flag().=C2=A0 A BPF raw_tp program attached to > sched_set_need_resched executes synchronously inside __bpf_trace_run(). > On return, __bpf_trace_run() drops the RCU lock with > rcu_read_unlock_migrate(), which on the preempt-or-BH-disabled path > calls set_need_resched_current() -> set_tsk_need_resched() again. >=20 > set_tsk_thread_flag() follows the tracepoint call, so every re-entrant > frame sees TIF_NEED_RESCHED clear and calls __trace_set_need_resched() > again: >=20 > =C2=A0 BUG: TASK stack guard page was hit at ffffc9001224ff98 > =C2=A0 Oops: stack guard page: 0000 [#1] SMP KASAN PTI > =C2=A0 RIP: 0010:__bpf_trace_sched_set_need_resched_tp+0x1c/0x190 > =C2=A0 Call Trace: > =C2=A0=C2=A0 trace_sched_set_need_resched_tp+0x110/0x130 > =C2=A0=C2=A0 set_tsk_need_resched include/linux/sched.h:2076 > =C2=A0=C2=A0 set_need_resched_current include/linux/sched.h:2094 > =C2=A0=C2=A0 rcu_read_unlock_special+0x43a/0x440 > =C2=A0=C2=A0 __rcu_read_unlock+0x9e/0x120 > =C2=A0=C2=A0 rcu_read_unlock_migrate+0xa9/0x240 > =C2=A0=C2=A0 __bpf_trace_run+0x131/0x180 > =C2=A0=C2=A0 bpf_trace_run3+0x333/0x430 > =C2=A0=C2=A0 __bpf_trace_sched_set_need_resched_tp+0x13a/0x190 > =C2=A0=C2=A0 trace_sched_set_need_resched_tp+0x110/0x130 > =C2=A0=C2=A0 set_tsk_need_resched include/linux/sched.h:2076 > =C2=A0=C2=A0 ... >=20 > __resched_curr() has the same ordering, firing the tracepoint before > setting the flag via set_ti_thread_flag() or set_nr_and_not_polling(). > Fix it for consistency. >=20 > Replace the separate test_tsk_thread_flag() + set_tsk_thread_flag() pair > in set_tsk_need_resched() with test_and_set_tsk_thread_flag().=C2=A0 In > __resched_curr(), move the tracepoint call after the flag is set in > each path. >=20 > Fixes: adcc3bfa8806 ("sched: Adapt sched tracepoints for RV task model") > Signed-off-by: Sechang Lim > --- Works fine with the existing rv monitors, thanks! Acked-by: Gabriele Monaco > v3: > =C2=A0- reorder need_ipi variable. (K Prateek Nayak) >=20 > v2: > =C2=A0- https://lore.kernel.org/all/20260627081657.499781-1-rhkrqnwk98@gm= ail.com/ >=20 > v1: > =C2=A0- https://lore.kernel.org/all/20260625065656.392182-1-rhkrqnwk98@gm= ail.com/ >=20 > =C2=A0include/linux/sched.h | 5 ++--- > =C2=A0kernel/sched/core.c=C2=A0=C2=A0 | 7 +++++-- > =C2=A02 files changed, 7 insertions(+), 5 deletions(-) >=20 > diff --git a/include/linux/sched.h b/include/linux/sched.h > index ee06cba5c6f5..c9efd08dae92 100644 > --- a/include/linux/sched.h > +++ b/include/linux/sched.h > @@ -2071,10 +2071,9 @@ static inline int test_tsk_thread_flag(struct > task_struct *tsk, int flag) > =C2=A0 > =C2=A0static inline void set_tsk_need_resched(struct task_struct *tsk) > =C2=A0{ > - if (tracepoint_enabled(sched_set_need_resched_tp) && > - =C2=A0=C2=A0=C2=A0 !test_tsk_thread_flag(tsk, TIF_NEED_RESCHED)) > + if (!test_and_set_tsk_thread_flag(tsk, TIF_NEED_RESCHED) && > + =C2=A0=C2=A0=C2=A0 tracepoint_enabled(sched_set_need_resched_tp)) > =C2=A0 __trace_set_need_resched(tsk, TIF_NEED_RESCHED); > - set_tsk_thread_flag(tsk,TIF_NEED_RESCHED); > =C2=A0} > =C2=A0 > =C2=A0static inline void clear_tsk_need_resched(struct task_struct *tsk) > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index b8871449d3c6..19de28f0d85a 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -1171,6 +1171,7 @@ static void __resched_curr(struct rq *rq, int tif) > =C2=A0{ > =C2=A0 struct task_struct *curr =3D rq->curr; > =C2=A0 struct thread_info *cti =3D task_thread_info(curr); > + bool need_ipi; > =C2=A0 int cpu; > =C2=A0 > =C2=A0 lockdep_assert_rq_held(rq); > @@ -1187,15 +1188,17 @@ static void __resched_curr(struct rq *rq, int tif= ) > =C2=A0 > =C2=A0 cpu =3D cpu_of(rq); > =C2=A0 > - trace_sched_set_need_resched_tp(curr, cpu, tif); > =C2=A0 if (cpu =3D=3D smp_processor_id()) { > =C2=A0 set_ti_thread_flag(cti, tif); > =C2=A0 if (tif =3D=3D TIF_NEED_RESCHED) > =C2=A0 set_preempt_need_resched(); > + trace_sched_set_need_resched_tp(curr, cpu, tif); > =C2=A0 return; > =C2=A0 } > =C2=A0 > - if (set_nr_and_not_polling(cti, tif)) { > + need_ipi =3D set_nr_and_not_polling(cti, tif); > + trace_sched_set_need_resched_tp(curr, cpu, tif); > + if (need_ipi) { > =C2=A0 if (tif =3D=3D TIF_NEED_RESCHED) > =C2=A0 smp_send_reschedule(cpu); > =C2=A0 } else {