tetragon: Use do_task_dead probe for exit sensor #1012
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olsajiri
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failure is not related to this PR as it is tracked here: #1025 |
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Hooking on do_task_dead kernel function, which is the last one the
task would execute after exiting. It's stable since v4.19, so it's
safe to hook for us.
To find out if we are the last thread of execution in the task we
use current->signal->live counter (thanks Djalal! ;-) )
It's initialized for thread leader:
clone {
copy_process
copy_signal
atomic_set(&sig->live, 1);
}
Incremented for each new thread:
clone {
copy_process
atomic_inc(¤t->signal->live);
...
wake_up_new_task
}
Decremented for each exiting thread:
do_exit {
atomic_dec_and_test(&tsk->signal->live);
...
do_task_dead
__schedule
BUG
}
If task->signal->live == 0 we are the last thread of execution and we
won't race with another clone, because there's no other thread to call
it (current thread is in do_exit).
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Adding extra threads to the exit-leader test prog. Spawning 2 threads directly from leader and another 2 from the newly created threads. Signed-off-by: Jiri Olsa <jolsa@kernel.org>
kkourt
approved these changes
Jun 1, 2023
| * | ||
| * If task->signal->live == 0 we are the last thread of execution and we | ||
| * won't race with another clone, because there's no other thread to call | ||
| * it (current thread is in do_exit). |
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Thanks for the nice comment :)
kkourt
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Hooking on do_task_dead kernel function, which is the last one the
task would execute after exiting. It's stable since v4.19, so it's
safe to hook for us.
To find out if we are the last thread of execution in the task we
use current->signal->live counter (thanks Djalal! ;-) )
It's initialized for thread leader:
Incremented for each new thread:
Decremented for each exiting thread:
If task->signal->live == 0 we are the last thread of execution and we
won't race with another clone, because there's no other thread to call
it (current thread is in do_exit).