Jens,
I'll read this version tomorrow, but:
On 10/01, Jens Axboe wrote:
>
> static inline int signal_pending(struct task_struct *p)
> {
> - return unlikely(test_tsk_thread_flag(p,TIF_SIGPENDING));
> +#ifdef TIF_TASKWORK
> + /*
> + * TIF_TASKWORK isn't really a signal, but it requires the same
> + * behavior of restarting the system call to force a kernel/user
> + * transition.
> + */
> + return unlikely(test_tsk_thread_flag(p, TIF_SIGPENDING) ||
> + test_tsk_thread_flag(p, TIF_TASKWORK));
> +#else
> + return unlikely(test_tsk_thread_flag(p, TIF_SIGPENDING));
> +#endif
This change alone is already very wrong.
signal_pending(task) == T means that this task will do get_signal() as
soon as it can, and this basically means you can't "divorce" SIGPENDING
and TASKWORK.
Simple example. Suppose we have a single-threaded task T.
Someone does task_work_add(T, TWA_SIGNAL). This makes signal_pending()==T
and this is what we need.
Now suppose that another task sends a signal to T before T calls
task_work_run() and clears TIF_TASKWORK. In this case SIGPENDING won't
be set because signal_pending() is already set (see wants_signal), and
this means that T won't notice this signal.
Oleg.
