Date: Sat, 8 Feb 2003 18:26:05 +1100 From: Tim Robbins <tjr@FreeBSD.org> To: Julian Elischer <julian@FreeBSD.org> Cc: src-committers@FreeBSD.org, cvs-src@FreeBSD.org, cvs-all@FreeBSD.org, legacy-committers@FreeBSD.org Subject: Re: cvs commit: src/sys/sys proc.h src/sys/kern kern_clock.c kern_exit.c subr_prof.c Message-ID: <20030208182605.A43083@dilbert.robbins.dropbear.id.au> In-Reply-To: <200302080258.h182wGsb081303@repoman.freebsd.org>; from julian@FreeBSD.org on Fri, Feb 07, 2003 at 06:58:16PM -0800 References: <200302080258.h182wGsb081303@repoman.freebsd.org>
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On Fri, Feb 07, 2003 at 06:58:16PM -0800, Julian Elischer wrote:
> julian 2003/02/07 18:58:16 PST
>
> Modified files:
> sys/sys proc.h
> sys/kern kern_clock.c kern_exit.c subr_prof.c
> Log:
> A little infrastructure, preceding some upcoming changes
> to the profiling and statistics code.
>
> Submitted by: DavidXu@
> Reviewed by: peter@
I don't understand how the locking in addupc_task() can be correct.
Block 1:
+ PROC_LOCK(p);
+ mtx_lock_spin(&sched_lock);
+ if (!(p->p_sflag & PS_PROFIL)) {
+ mtx_unlock_spin(&sched_lock);
+ PROC_UNLOCK(p);
+ return;
+ }
+ p->p_profthreads++;
+ mtx_unlock_spin(&sched_lock);
+ PROC_UNLOCK(p);
Block 2:
+ PROC_LOCK(p);
+ if (--p->p_profthreads == 0) {
+ if (p->p_sflag & PS_STOPPROF) {
+ wakeup(&p->p_profthreads);
+ stop = 0;
+ }
}
[...]
+ PROC_UNLOCK(p);
It looks like sched_lock should be locked before accessing p_sflag in
"Block 2". In "Block 1", I don't see why the proc needs to be locked
while accessing p_sflag; that block could be rewritten to only hold one
lock at a time. Protecting p_profthreads with sched_lock instead of the
proc lock might help, too, since every access to p_profthreads is done
(or could easily be done) while holding sched_lock. This would make it
unnecessary to hold the proc lock while calling stopprofclock().
Locking for the profil() syscall seems to be broken, too. A comment says:
/* Block profile interrupts while changing state. */
but it doesn't actually block anything. It looks like there are races
between it and addupc_{intr,task}().
Tim
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