On May 1, 2008, at 11:14 AM, Scott Wood wrote:

On Thu, May 01, 2008 at 08:17:07AM -0500, Kumar Gala wrote:

quoted

On May 1, 2008, at 3:24 AM, Paul Mackerras wrote:

quoted

The most common cases are (a) something that ultimately generates
input on a tty (e.g. a character arriving on a serial port) and that
input turns out to be a ^C or similar, or (b) something that signals
I/O completion and the program doing the I/O has requested
notification by a SIGIO.  But in general any driver code can send a
signal to userspace if it wants.

And, of course, SIGALRM and similar timer mechanisms.

quoted

ok.  Was just wondering how the async exception know that the signal
it wanted to send belonged to the particular process that is running.
But I guess there are cases that the signal is really intended for  
who
ever is currently running?

No, it knows based on its own data structures who it's intended for --
and sometimes that happens to be the currently running process.

Let me ask the question differently.  Are there cases that some event  
occurs in the system and a signal is delivered to the current process  
regardless of what that process is.  I'm guessing so, based on the tty  
example.

So for the specific case I'm looking at (kprobes & debug exceptions  
from kernel space), I think its reasonable to BUG_ON() if thread_info- 
 >flags changes such that TIF_SIGPENDING or TIF_NEED_RESCHED get set  
we aren't from user-space.

- k