Re: Signal delivery

[Mulyadi Santosa <mulyadi.santosa@xxxxxxxxx>]

Hi
>     Need to clarify some concepts about signaling mechanism in linux 
> kernel
> 2.4 and 2.6 ?
>
> What time the signal to a process is really delivered --
> 1. After moving from kernel space to user space - yes
personal comment: yes, if it returns to the target process that received 
the signal. Just to be precise. And I think what you really mean here is 
actually "handled", because signal is actually queued right at the time 
other process send a signal to it.

> 2. After the process in kernel space wakes up from
> interruptible/uninterruptible sleep -- ??

Ok, do you mean "handled"? As far as I can tell by looking from the 
code, unless you manually check the sigpending flag, returning to kernel 
space after a sleep won't make a signal handler executed.
> 3. Can a kernel thread be signaled ? What time does it check for its 
> pending
> signals ?
I forgot the detail, but yes basically you can do that. Of course, it 
doesn't check by default. it is you that must check the sigpending 
manually. Usually, all the kernel threads block all the signal (IIRC 
from kthread_create() ) so you must manually unblock the spesific signal 
number.
> 4. Can a user process signal a kernel thread (visible through ps), or 
> only
> another kernel process can do that ? How is it implemented ?

See above.

regards,

Mulyadi


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