dtrace pid provider on entry == Trace/BPT trap process

[Mark Johnston]

On Tue, Nov 07, 2017 at 12:15:22PM +0100, Andreas Longwitz wrote:
> Maybe the following is of interest for DTrace experts:
> 
> >> I use FreeBSD 10.3-STABLE r317936 with updated /usr/lib/dtrace/ip.c and
> >> see an issue that in my opinion should have been solved in r269342:
> > 
> > 10.3 would be missing a number of other fixes for issues that might
> > cause the symptom you're seeing. Unfortunately, userland DTrace is not
> > very usable on FreeBSD before 11.0.
> 
> I have repeated my looptest on a server running FreeBSD 12.0-CURRENT #0
> r324306 with GENERIC kernel. I saw the same problem as described before
> for FreeBSD 10.3-Stable r317936:
> 
> Nov  7 10:54:09 <kern.info> dssbkp2 kernel: pid 38041 (looptest), uid
> 1003: exited on signal 5
> 
> Further I saw following error message from dtrace:
> 
>   dtrace: failed to grab pid 38622: Device busy.
> 
> After some minutes playing around the server crashed with
> 
> panic: PHOLD of exiting process 0xfffff80004c80540

Sorry for the delayed reply. I think this assertion is bogus: the
process in question is already held at this point, so it can't continue
exiting anyway. I think the patch below will address this and the
SIGTRAP crashes. Could you give it a try?

diff --git a/sys/cddl/compat/opensolaris/kern/opensolaris_proc.c b/sys/cddl/compat/opensolaris/kern/opensolaris_proc.c
index 652fa8928589..63db17199fb4 100644
--- a/sys/cddl/compat/opensolaris/kern/opensolaris_proc.c
+++ b/sys/cddl/compat/opensolaris/kern/opensolaris_proc.c
@@ -35,9 +35,7 @@ uread(proc_t *p, void *kaddr, size_t len, uintptr_t uaddr)
 {
 	ssize_t n;
 
-	PHOLD(p);
 	n = proc_readmem(curthread, p, uaddr, kaddr, len);
-	PRELE(p);
 	if (n != len)
 		return (ENOMEM);
 	return (0);
@@ -48,9 +46,7 @@ uwrite(proc_t *p, void *kaddr, size_t len, uintptr_t uaddr)
 {
 	ssize_t n;
 
-	PHOLD(p);
 	n = proc_writemem(curthread, p, uaddr, kaddr, len);
-	PRELE(p);
 	if (n != len)
 		return (ENOMEM);
 	return (0);
diff --git a/sys/cddl/contrib/opensolaris/uts/common/dtrace/fasttrap.c b/sys/cddl/contrib/opensolaris/uts/common/dtrace/fasttrap.c
index 82353cbb235d..d721270fd425 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/dtrace/fasttrap.c
+++ b/sys/cddl/contrib/opensolaris/uts/common/dtrace/fasttrap.c
@@ -64,6 +64,7 @@
 #include <sys/dtrace_bsd.h>
 #include <sys/eventhandler.h>
 #include <sys/rmlock.h>
+#include <sys/smp.h>
 #include <sys/sysent.h>
 #include <sys/sysctl.h>
 #include <sys/u8_textprep.h>
@@ -1097,6 +1098,8 @@ fasttrap_tracepoint_disable(proc_t *p, fasttrap_probe_t *probe, uint_t index)
 		p->p_dtrace_count--;
 	}
 
+	(void)quiesce_all_cpus("fasttrap", 0);
+
 	/*
 	 * Remove the probe from the hash table of active tracepoints.
 	 */
diff --git a/sys/cddl/contrib/opensolaris/uts/intel/dtrace/fasttrap_isa.c b/sys/cddl/contrib/opensolaris/uts/intel/dtrace/fasttrap_isa.c
index d6655a0b3c55..0364aaf55094 100644
--- a/sys/cddl/contrib/opensolaris/uts/intel/dtrace/fasttrap_isa.c
+++ b/sys/cddl/contrib/opensolaris/uts/intel/dtrace/fasttrap_isa.c
@@ -1715,11 +1715,7 @@ fasttrap_pid_probe(struct reg *rp)
 
 		ASSERT(i <= sizeof (scratch));
 
-#ifdef illumos
 		if (fasttrap_copyout(scratch, (char *)addr, i)) {
-#else
-		if (uwrite(p, scratch, i, addr)) {
-#endif
 			fasttrap_sigtrap(p, curthread, pc);
 			new_pc = pc;
 			break;