RE: [musl] Fix the return value of pthread_getschedparam in musl libc

[tangyizhou <tangyizhou@huawei.com>]

> There's not such an issue. t->killlock is held so that this can't happen, and more importantly, so that the thread can't exit and the tid be reassigned to a new thread or process that would wrongly be acted upon.

Sorry for late reply.

t->killlock is held only in pthread functions, and it won't work in the following situation.  Assuming process A is running on CPU core 0, process B is running on CPU core 1, process C is running on CPU core 2. Process A calls pthread_getschedparam() to query the information of process B. After SYS_sched_getparam succeeds and before SYS_sched_getscheduler starts,  we assume the scheduling timeslice of A is running out, then A is put in the runqueue of the kernel. This is a chance for C to call kill() to kill B. When A is running again, SYS_sched_getparam returns -ESRCH.

Process B may be terminated due to other reasons when A is put in the runqueue. For example, B is running and encounters a bus error, then B is terminated because of SIGBUS signal.

It very hard to see these situations, but they exist in a theoretical way. There isn't such an issue for the implementation of pthread_getschedparam() of glibc.


Yizhou