Messages in this thread | | | Date | Sun, 26 Apr 2020 19:22:07 +0200 | From | Oleg Nesterov <> | Subject | Re: [PATCH v3 2/6] posix-cpu-timers: Use PIDTYPE_TGID to simplify the logic in lookup_task |
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Eric,
I am sick today and can't read the code, but I feel this patch is not right ... please correct me.
So, iiuc when posix_cpu_timer_create() is called and CPUCLOCK_PERTHREAD is false we roughly have
task = pid_task(pid, PIDTYPE_TGID); // lookup_task()
/* WINDOW */
timer->it.cpu.pid = = get_task_pid(task, PIDTYPE_TGID) // posix_cpu_timer_create()
Now suppose that we race with mt-exec and this "task" is the old leader; it can be release_task()'ed in the WINDOW above and then get_task_pid() will return NULL.
That is why I suggested to change lookup_task() to return "struct pid*" to eliminate the pid -> task -> pid transition.
Apart from the same_thread_group() check for the "thread" case we do not need task_struct at all, lookup_task() can do
if (thread) { p = pid_task(pid, PIDTYPE_PID); if (p && !same_thread_group(p, current)) pid = NULL; } else { ... gettime check ...
if (!pid_has_task(pid, PIDTYPE_TGID)) pid = NULL; }
return pid;
No?
Oleg.
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