Re: [PATCH v3 1/6] posix-cpu-timers: Always call __get_task_for_clock holding rcu_read_lock

Eric W. Biederman
2020-04-27T11:57:00Z

Thomas Gleixner <tglx@linutronix.de> writes:

> ebiederm@xmission.com (Eric W. Biederman) writes:
>
>> This allows the getref flag to be removed and the callers can
>> than take a task reference if needed.
>
> That changelog lacks any form of information why this should be
> changed. I can see the point vs. patch 2, but pretty please put coherent
> explanations into each patch.

Well excess flags bad. But in this case I can do even better.

The code no longer takes a reference on task_struct so this patch
removes unnecessary code.

I will see if I can say that better.

>> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
>> ---
>> kernel/time/posix-cpu-timers.c | 41 +++++++++++++++++-----------------
>> 1 file changed, 21 insertions(+), 20 deletions(-)
>>
>> diff --git a/kernel/time/posix-cpu-timers.c b/kernel/time/posix-cpu-timers.c
>> index 2fd3b3fa68bf..eba41c70f0f0 100644
>> --- a/kernel/time/posix-cpu-timers.c
>> +++ b/kernel/time/posix-cpu-timers.c
>> @@ -86,36 +86,34 @@ static struct task_struct *lookup_task(const pid_t pid, bool thread,
>> }
>>
>> static struct task_struct *__get_task_for_clock(const clockid_t clock,
>> - bool getref, bool gettime)
>> + bool gettime)
>> {
>> const bool thread = !!CPUCLOCK_PERTHREAD(clock);
>> const pid_t pid = CPUCLOCK_PID(clock);
>> - struct task_struct *p;
>>
>> if (CPUCLOCK_WHICH(clock) >= CPUCLOCK_MAX)
>> return NULL;
>>
>> - rcu_read_lock();
>> - p = lookup_task(pid, thread, gettime);
>> - if (p && getref)
>> - get_task_struct(p);
>> - rcu_read_unlock();
>> - return p;
>> + return lookup_task(pid, thread, gettime);
>> }
>>
>> static inline struct task_struct *get_task_for_clock(const clockid_t clock)
>> {
>> - return __get_task_for_clock(clock, true, false);
>> + return __get_task_for_clock(clock, false);
>> }
>>
>> static inline struct task_struct *get_task_for_clock_get(const clockid_t clock)
>> {
>> - return __get_task_for_clock(clock, true, true);
>> + return __get_task_for_clock(clock, true);
>> }
>>
>> static inline int validate_clock_permissions(const clockid_t clock)
>> {
>> - return __get_task_for_clock(clock, false, false) ? 0 : -EINVAL;
>> + int ret;
>
> New line between declarations and code please.
>
>> + rcu_read_lock();
>> + ret = __get_task_for_clock(clock, false) ? 0 : -EINVAL;
>> + rcu_read_unlock();
>> + return ret;
>> }
>
> Thanks,
>
> tglx