Messages in this thread | | | From | Roland McGrath <> | Subject | Re: [patch 20/24] perfmon: system calls interface | Date | Wed, 3 Dec 2008 17:05:26 -0800 (PST) |
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> > + /* > > + * cannot attach to a kernel thread > > + */ > > + if (!task->mm) {
This should test (task->flags & PF_KTHREAD). (But it's superfluous anyway.)
> > + /* > > + * cannot attach to a zombie task > > + */ > > + if (task->exit_state == EXIT_ZOMBIE || task->exit_state == EXIT_DEAD) {
The usual test to write here is just "if (task->exit_state)". (But it's superfluous anyway.)
> Thirdly, the check for ->exit_state in pfm_task_incompatible() is not > needed: we've just passed ptrace_check_attach() so we know we just > transitioned the task to task->state == TASK_TRACED.
Correct.
> If you _ever_ see a task exit TASK_TRACED and go zombie or dead from > there without this code allowing it that means the whole state machine > with ptrace is borked up by perfmon.
Is always possible for a TASK_TRACED task to suddenly die via SIGKILL, and it's even possible it will be reaped (EXIT_DEAD) despite ptrace, in the de_thread() (MT exec) case. This race is tolerable for everything ptrace does (it holds a task ref, and the arch code copes). It must also be tolerated by the perfmon code.
> For example i dont see where the perfmon-control task parents itself as > the exclusive debugger (parent) of the debuggee-task.
ptrace_check_attach() ensures that this is so.
Thanks, Roland
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