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This allows a BPF tracepoint program to recursively invoke > >the same tracepoint while leaving its RCU read-side critical section. > > > >If rcu_read_unlock_special() must defer a quiescent state while > >preemption or interrupts are disabled, it calls > >set_need_resched_current(). Since TIF_NEED_RESCHED is still clear, this > >emits the tracepoint again and repeats until the kernel stack overflows: > > > > __trace_set_need_resched() > > bpf_trace_run3() > > rcu_read_unlock_migrate() > > rcu_read_unlock_special() > > set_need_resched_current() > > set_tsk_need_resched() > > __trace_set_need_resched() > > > >Set the thread flag before emitting the tracepoint in both > >set_tsk_need_resched() and __resched_curr(). For a remote reschedule, > >retain the result of set_nr_and_not_polling() so that tracing remains > >ahead of IPI delivery while still observing the updated flag. > > > >Fixes: adcc3bfa8806 ("sched: Adapt sched tracepoints for RV task model") > >Signed-off-by: Andrea Righi > >--- > > Hi Andrea, > > Isn't this mostly what was done in [1]? I wonder if that patch was just forgotten. > > There was a discussion that apparently didn't go anywhere, but it doesn't look like a blocker for the change to me. > It is **exactly** the same fix! I hit the same issue and missed Sechang's series. There's also a v3: https://lore.kernel.org/all/20260630084750.2792851-1-rhkrqnwk98@gmail.com/ We can ignore this one and go with Sechang's. Sorry for the noise. Thanks, -Andrea > Thanks, > Gabriele > > [1] - https://lore.kernel.org/lkml/20260627081657.499781-1-rhkrqnwk98@gmail.com > > > include/linux/sched.h | 5 ++++- > > kernel/sched/core.c | 7 +++++-- > > 2 files changed, 9 insertions(+), 3 deletions(-) > > > >diff --git a/include/linux/sched.h b/include/linux/sched.h > >index 59f6366fdf501..6003dcd080e6c 100644 > >--- a/include/linux/sched.h > >+++ b/include/linux/sched.h > >@@ -2105,8 +2105,11 @@ static inline int test_tsk_thread_flag(struct task_struct *tsk, int flag) > > static inline void set_tsk_need_resched(struct task_struct *tsk) > > { > > if (tracepoint_enabled(sched_set_need_resched_tp) && > >- !test_tsk_thread_flag(tsk, TIF_NEED_RESCHED)) > >+ !test_tsk_thread_flag(tsk, TIF_NEED_RESCHED)) { > >+ set_tsk_thread_flag(tsk, TIF_NEED_RESCHED); > > __trace_set_need_resched(tsk, TIF_NEED_RESCHED); > >+ return; > >+ } > > set_tsk_thread_flag(tsk,TIF_NEED_RESCHED); > > } > > > >diff --git a/kernel/sched/core.c b/kernel/sched/core.c > >index 91f059a556950..aed403fd2f82e 100644 > >--- a/kernel/sched/core.c > >+++ b/kernel/sched/core.c > >@@ -1196,6 +1196,7 @@ static void __resched_curr(struct rq *rq, int tif) > > { > > struct task_struct *curr = rq->curr; > > struct thread_info *cti = task_thread_info(curr); > >+ bool send_ipi; > > int cpu; > > > > lockdep_assert_rq_held(rq); > >@@ -1212,15 +1213,17 @@ static void __resched_curr(struct rq *rq, int tif) > > > > cpu = cpu_of(rq); > > > >- trace_sched_set_need_resched_tp(curr, cpu, tif); > > if (cpu == smp_processor_id()) { > > set_ti_thread_flag(cti, tif); > > if (tif == TIF_NEED_RESCHED) > > set_preempt_need_resched(); > >+ trace_sched_set_need_resched_tp(curr, cpu, tif); > > return; > > } > > > >- if (set_nr_and_not_polling(cti, tif)) { > >+ send_ipi = set_nr_and_not_polling(cti, tif); > >+ trace_sched_set_need_resched_tp(curr, cpu, tif); > >+ if (send_ipi) { > > if (tif == TIF_NEED_RESCHED) > > smp_send_reschedule(cpu); > > } else { >