Re: [PATCH 07/18] sched/fair: Add push task mechanism for fair

[Shrikanth Hegde <sshegde@linux.ibm.com>]

>>> +static int
>>> +select_task_rq_fair(struct task_struct *p, int prev_cpu, int wake_flags);
>>> +
>>> +/*
>>> + * See if the non running fair tasks on this rq can be sent on other CPUs
>>> + * that fits better with their profile.
>>> + */
>>> +static bool fair_push_task(struct rq *rq)
>>> +{
>>> +     struct task_struct *next_task;
>>> +     int prev_cpu, new_cpu;
>>> +     struct rq_flags rf;
>>> +     struct rq *cur_rq;
>>
>> You likely need below to keep clang's context tracking to be happy.
>>
>>          context_unsafe_alias(rq);
> 
> I just noticed that I didn't answer to this one
> 
> Why should I need this ?
> 
> rq remains the same in fair_push_task(). I'm using rq and new_rq to
> differentiate both current and new rq
> 
>>
I tried to use clang-23 and get below with the series applied.
It may not be exactly here. But somewhere.

make LLVM=/opt/llvm-23/bin/ \
         KCFLAGS="-Werror=thread-safety-analysis" \
         V=1 kernel/sched/fair.o

kernel/sched/fair.c:9971:2: error: releasing raw_spinlock 'rq_lockp(rq)' that was not held [-Werror,-Wthread-safety-analysis]
  9971 |         raw_spin_rq_unlock(rq);
       |         ^
kernel/sched/fair.c:9983:2: error: raw_spinlock 'rq_lockp(rq)' is not held on every path through here [-Werror,-Wthread-safety-analysis]
  9983 |         raw_spin_unlock(&next_task->pi_lock);
       |         ^
./include/linux/spinlock.h:279:32: note: expanded from macro 'raw_spin_unlock'
   279 | #define raw_spin_unlock(lock)           _raw_spin_unlock(lock)
       |                                         ^
kernel/sched/fair.c:9980:2: note: raw_spinlock acquired here
  9980 |         raw_spin_rq_lock(rq);
       |         ^
kernel/sched/fair.c:10085:2: error: releasing raw_spinlock 'rq_lockp(rq)' that was not held [-Werror,-Wthread-safety-analysis]
  10085 |         rq_unlock(rq, rf);
        |         ^
kernel/sched/fair.c:10093:1: error: raw_spinlock 'rq_lockp(rq)' is not held on every path through here
       [-Werror,-Wthread-safety-analysis]
  10093 | }
        | ^
kernel/sched/fair.c:10090:2: note: raw_spinlock acquired here
  10090 |         rq_lock(rq, rf);
        |         ^