svn commit: r259535 - in head/sys: cddl/contrib/opensolaris/uts/intel/dtrace kern

[Mark Johnston]

Author: markj
Date: Wed Dec 18 01:41:52 2013
New Revision: 259535
URL: http://svnweb.freebsd.org/changeset/base/259535

Log:
  The fasttrap fork handler is responsible for removing tracepoints in the
  child process that were inherited from its parent. However, this should
  not be done in the case of a vfork, since the fork handler ends up removing
  the tracepoints from the shared vm space, and userland DTrace probes in the
  parent will no longer fire as a result.
  
  Now the child of a vfork may trigger userland DTrace probes enabled in its
  parent, so modify the fasttrap probe handler to handle this case and handle
  the child process in the same way that it would handle the traced process.
  In particular, if once traces function foo() in a process that vforks, and
  the child calls foo(), fasttrap will treat this call as having come from the
  parent. This is the behaviour of the upstream code.
  
  While here, add #ifdef guards to some code that isn't present upstream.
  
  MFC after:	1 month

Modified:
  head/sys/cddl/contrib/opensolaris/uts/intel/dtrace/fasttrap_isa.c
  head/sys/kern/kern_fork.c

Modified: head/sys/cddl/contrib/opensolaris/uts/intel/dtrace/fasttrap_isa.c
==============================================================================
--- head/sys/cddl/contrib/opensolaris/uts/intel/dtrace/fasttrap_isa.c	Wed Dec 18 01:27:30 2013	(r259534)
+++ head/sys/cddl/contrib/opensolaris/uts/intel/dtrace/fasttrap_isa.c	Wed Dec 18 01:41:52 2013	(r259535)
@@ -1001,6 +1001,9 @@ int
 fasttrap_pid_probe(struct reg *rp)
 {
 	proc_t *p = curproc;
+#if !defined(sun)
+	proc_t *pp;
+#endif
 	uintptr_t pc = rp->r_rip - 1;
 	uintptr_t new_pc = 0;
 	fasttrap_bucket_t *bucket;
@@ -1036,24 +1039,32 @@ fasttrap_pid_probe(struct reg *rp)
 	curthread->t_dtrace_regv = 0;
 #endif
 
-#if defined(sun)
 	/*
 	 * Treat a child created by a call to vfork(2) as if it were its
 	 * parent. We know that there's only one thread of control in such a
 	 * process: this one.
 	 */
+#if defined(sun)
 	while (p->p_flag & SVFORK) {
 		p = p->p_parent;
 	}
-#endif
 
-	PROC_LOCK(p);
-	_PHOLD(p);
 	pid = p->p_pid;
-#if defined(sun)
 	pid_mtx = &cpu_core[CPU->cpu_id].cpuc_pid_lock;
 	mutex_enter(pid_mtx);
+#else
+	pp = p;
+	sx_slock(&proctree_lock);
+	while (pp->p_vmspace == pp->p_pptr->p_vmspace)
+		pp = pp->p_pptr;
+	pid = pp->p_pid;
+	sx_sunlock(&proctree_lock);
+	pp = NULL;
+
+	PROC_LOCK(p);
+	_PHOLD(p);
 #endif
+
 	bucket = &fasttrap_tpoints.fth_table[FASTTRAP_TPOINTS_INDEX(pid, pc)];
 
 	/*
@@ -1073,9 +1084,10 @@ fasttrap_pid_probe(struct reg *rp)
 	if (tp == NULL) {
 #if defined(sun)
 		mutex_exit(pid_mtx);
-#endif
+#else
 		_PRELE(p);
 		PROC_UNLOCK(p);
+#endif
 		return (-1);
 	}
 
@@ -1197,9 +1209,10 @@ fasttrap_pid_probe(struct reg *rp)
 	 * tracepoint again later if we need to light up any return probes.
 	 */
 	tp_local = *tp;
-	PROC_UNLOCK(p);
 #if defined(sun)
 	mutex_exit(pid_mtx);
+#else
+	PROC_UNLOCK(p);
 #endif
 	tp = &tp_local;
 
@@ -1749,7 +1762,7 @@ fasttrap_pid_probe(struct reg *rp)
 #if defined(sun)
 		if (fasttrap_copyout(scratch, (char *)addr, i)) {
 #else
-		if (uwrite(curproc, scratch, i, addr)) {
+		if (uwrite(p, scratch, i, addr)) {
 #endif
 			fasttrap_sigtrap(p, curthread, pc);
 			new_pc = pc;
@@ -1808,10 +1821,12 @@ done:
 
 	rp->r_rip = new_pc;
 
+#if !defined(sun)
 	PROC_LOCK(p);
 	proc_write_regs(curthread, rp);
 	_PRELE(p);
 	PROC_UNLOCK(p);
+#endif
 
 	return (0);
 }

Modified: head/sys/kern/kern_fork.c
==============================================================================
--- head/sys/kern/kern_fork.c	Wed Dec 18 01:27:30 2013	(r259534)
+++ head/sys/kern/kern_fork.c	Wed Dec 18 01:41:52 2013	(r259535)
@@ -676,12 +676,12 @@ do_fork(struct thread *td, int flags, st
 
 #ifdef KDTRACE_HOOKS
 	/*
-	 * Tell the DTrace fasttrap provider about the new process
-	 * if it has registered an interest. We have to do this only after
-	 * p_state is PRS_NORMAL since the fasttrap module will use pfind()
-	 * later on.
+	 * Tell the DTrace fasttrap provider about the new process so that any
+	 * tracepoints inherited from the parent can be removed. We have to do
+	 * this only after p_state is PRS_NORMAL since the fasttrap module will
+	 * use pfind() later on.
 	 */
-	if (dtrace_fasttrap_fork)
+	if ((flags & RFMEM) == 0 && dtrace_fasttrap_fork)
 		dtrace_fasttrap_fork(p1, p2);
 #endif
 	if ((p1->p_flag & (P_TRACED | P_FOLLOWFORK)) == (P_TRACED |