cvs commit: src/sys/ddb db_ps.c src/sys/i386/i386 trap.c vm86.c src/sys/kern init_main.c kern_clock.c kern_exit.c kern_fork.c kern_resource.c kern_sig.c kern_synch.c kern_upcall.c lwkt_thread.c usched_bsd4.c vfs_aio.c src/sys/netproto/smb ...

Simon 'corecode' Schubert corecode at
Tue Oct 11 11:43:29 PDT 2005

Matthew Dillon wrote:

    We want to avoid using LIST_FIRST for this case.  e.g. you are doing 

    p = curproc;
    lp = LIST_FIRST(...)
    Instead of doing that, use curthread->td_lwp (assuming its set up at that point).
Yea, my bad, I overlooked that.


    p->p_usched->heuristic_exiting(q, p);
    p->p_usched->heuristic_exiting(td->td_lwp, &p->p_lwp);
    Avoid using &p->p_lwp if possible, since the embedded lwp is going to go away at 
    some point.  If this code is going to have to deal with all the LWPs then put an
    XXX comment in there or do a LIST_FOREACH and/or otherwise assert that there is
    only one lwp so this doesn't bite us in the ass later on.
My idea was to use p_lwp to signal that this place needs to be revisited 
in one way or the other instead of using a bogus LIST_FIRST(). This 
helps me keeping correct code which i can find again lateron by 
searching for p_lwp.

In the process of converting functions to use lwp, the use of p->p_lwp 
will automatically be replaced by lp.


    Same issue.  Deserves a comment at least (or maybe fork should take a proc pointer,
    since you can't fork an LWP anyway).
-	p = &proc0;
-	error = fork1(p, RFPROC|RFMEM|RFNOWAIT, &np);
+	lp = &proc0.p_lwp;
+	error = fork1(lp, RFPROC|RFMEM|RFNOWAIT, &np);
Fork needs to take a lwp because the new proc's only lwp will be a copy 
of the current lwp.  When we split out lwp from proc we'll have a lwp0 


    Same issue.  I think it's becoming clear that we want fork*() to take a proc pointer.

-	error = fork1(&proc0, RFMEM | RFFDG | RFPROC | flags, &p2);
+	error = fork1(&proc0.p_lwp, RFMEM | RFFDG | RFPROC | flags, &p2);
-	start_forked_proc(&proc0, p2);
+	start_forked_proc(&proc0.p_lwp, p2);
Same again.  lwp0 will do the job here.


    Same issue.  Add XXX comment, KKASERT that there is only one thread if accessing
-		p->p_usched->remrunqueue(p);
+		p->p_usched->remrunqueue(&p->p_lwp);
No, we need to loop through all lwps, but I wanted to do this in a later 
step (3, I think).

    Same issue.

-			bigproc->p_usched->resetpriority(bigproc);
+			bigproc->p_usched->resetpriority(&bigproc->p_lwp);
    Why is this important?  Even though these steps are intermediate steps and
    will undergo further changes, we do not want the complexity of the work to introduce
    bugs as it progresses.  It is better to assert the assumed condition in the intermediate
    step and take a panic later on when you've forgotten something than for the system 
    to become corrupt and take hours to debug.
I try to avoid producing avalances by forcing all functions down the 
code path to use lwp as well, so I'm using p->p_lwp and lp->lwp_proc to 
keep stuf from propagating.  This won't introduce bugs at the moment, 
because they are exchangable.  As we proceed converting functions these 
uses will go away.  Basically p_lwp is a compiletime XXX:  if there is 
still code that uses p_lwp, we're not ready yet to use multiple threads 
per process.

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