linux kernel - How do waitpid and ptrace work together? -


going through source code of linux 4.12, can't wrap head around below code when task being ptraced.

do_wait()

will call

ptrace_do_wait(wo, tsk)

which call

wait_consider_task

for every thread tracing on. in turn call

wait_task_stopped

which find pid [pid = task_pid_vnr(p);] waitpid return, great.

but calls

put_task_struct(p);

which free task structure. if happens, how debugger wait on process/task again? entry added again somewhere, , if where?

can 1 explain flow me? thanks.

what mean "put_task_struct frees structure"? familiar reference counting? did see matching get_task_struct?

let's have @ code:

get_task_struct(p);

refcount incremented

pid = task_pid_vnr(p); why = ptrace ? cld_trapped : cld_stopped; read_unlock(&tasklist_lock);

the list of tasks unlocked. in principle can wait() on thread rid of structure due increased refcount

sched_annotate_sleep(); if (wo->wo_rusage)         getrusage(p, rusage_both, wo->wo_rusage); put_task_struct(p);

... , refcount decremented. if last ref, object freed. otherwise nothing happens.


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