MFC r303423:

Force SIGSTOP to be the first signal reported after the attach.

6 files changed, 73 insertions, 22 deletions

diff --git a/bin/ps/ps.1 b/bin/ps/ps.1
index 0ff3268..fdb4f1e 100644
--- a/bin/ps/ps.1
+++ b/bin/ps/ps.1
@@ -347,6 +347,7 @@ the include file
 .In sys/proc.h :
 .Bl -column P2_INHERIT_PROTECTED 0x00000001
 .It Dv "P2_INHERIT_PROTECTED" Ta No "0x00000001" Ta "New children get P_PROTECTED"
+.It Dv "P2_PTRACE_FSTP" Ta No "0x00000010" Ta "SIGSTOP from PT_ATTACH not yet handled"
 .El
 .It Cm label
 The MAC label of the process.
diff --git a/sys/kern/kern_exit.c b/sys/kern/kern_exit.c
index b6a697c..c362530 100644
--- a/sys/kern/kern_exit.c
+++ b/sys/kern/kern_exit.c
@@ -520,9 +520,12 @@ exit1(struct thread *td, int rv)
 			 */
 			clear_orphan(q);
 			q->p_flag &= ~(P_TRACED | P_STOPPED_TRACE);
+			q->p_flag2 &= ~P2_PTRACE_FSTP;
 			q->p_ptevents = 0;
-			FOREACH_THREAD_IN_PROC(q, tdt)
-				tdt->td_dbgflags &= ~TDB_SUSPEND;
+			FOREACH_THREAD_IN_PROC(q, tdt) {
+				tdt->td_dbgflags &= ~(TDB_SUSPEND | TDB_XSIG |
+				    TDB_FSTP);
+			}
 			kern_psignal(q, SIGKILL);
 		}
 		PROC_UNLOCK(q);
diff --git a/sys/kern/kern_fork.c b/sys/kern/kern_fork.c
index 600cb02..4d96840 100644
--- a/sys/kern/kern_fork.c
+++ b/sys/kern/kern_fork.c
@@ -1063,15 +1063,13 @@ fork_return(struct thread *td, struct trapframe *frame)
 			 * parent's children, do it now.
 			 */
 			dbg = p->p_pptr->p_pptr;
-			p->p_flag |= P_TRACED;
-			p->p_ptevents = PTRACE_DEFAULT;
-			p->p_oppid = p->p_pptr->p_pid;
+			proc_set_traced(p);
 			CTR2(KTR_PTRACE,
 		    "fork_return: attaching to new child pid %d: oppid %d",
 			    p->p_pid, p->p_oppid);
 			proc_reparent(p, dbg);
 			sx_xunlock(&proctree_lock);
-			td->td_dbgflags |= TDB_CHILD | TDB_SCX;
+			td->td_dbgflags |= TDB_CHILD | TDB_SCX | TDB_FSTP;
 			ptracestop(td, SIGSTOP);
 			td->td_dbgflags &= ~(TDB_CHILD | TDB_SCX);
 		} else {
diff --git a/sys/kern/kern_sig.c b/sys/kern/kern_sig.c
index 5996c60..2c37d76 100644
--- a/sys/kern/kern_sig.c
+++ b/sys/kern/kern_sig.c
@@ -2499,14 +2499,26 @@ ptracestop(struct thread *td, int sig)
 			PROC_SUNLOCK(p);
 			return (sig);
 		}
+
 		/*
-		 * Just make wait() to work, the last stopped thread
-		 * will win.
+		 * Make wait(2) work.  Ensure that right after the
+		 * attach, the thread which was decided to become the
+		 * leader of attach gets reported to the waiter.
+		 * Otherwise, just avoid overwriting another thread's
+		 * assignment to p_xthread.  If another thread has
+		 * already set p_xthread, the current thread will get
+		 * a chance to report itself upon the next iteration.
 		 */
-		p->p_xstat = sig;
-		p->p_xthread = td;
-		p->p_flag |= (P_STOPPED_SIG|P_STOPPED_TRACE);
-		sig_suspend_threads(td, p, 0);
+		if ((td->td_dbgflags & TDB_FSTP) != 0 ||
+		    ((p->p_flag & P2_PTRACE_FSTP) == 0 &&
+		    p->p_xthread == NULL)) {
+			p->p_xstat = sig;
+			p->p_xthread = td;
+			td->td_dbgflags &= ~TDB_FSTP;
+			p->p_flag2 &= ~P2_PTRACE_FSTP;
+			p->p_flag |= P_STOPPED_SIG | P_STOPPED_TRACE;
+			sig_suspend_threads(td, p, 0);
+		}
 		if ((td->td_dbgflags & TDB_STOPATFORK) != 0) {
 			td->td_dbgflags &= ~TDB_STOPATFORK;
 			cv_broadcast(&p->p_dbgwait);
@@ -2657,7 +2669,20 @@ issignal(struct thread *td)
 			SIG_STOPSIGMASK(sigpending);
 		if (SIGISEMPTY(sigpending))	/* no signal to send */
 			return (0);
-		sig = sig_ffs(&sigpending);
+		if ((p->p_flag & (P_TRACED | P_PPTRACE)) == P_TRACED &&
+		    (p->p_flag2 & P2_PTRACE_FSTP) != 0 &&
+		    SIGISMEMBER(sigpending, SIGSTOP)) {
+			/*
+			 * If debugger just attached, always consume
+			 * SIGSTOP from ptrace(PT_ATTACH) first, to
+			 * execute the debugger attach ritual in
+			 * order.
+			 */
+			sig = SIGSTOP;
+			td->td_dbgflags |= TDB_FSTP;
+		} else {
+			sig = sig_ffs(&sigpending);
+		}
 
 		if (p->p_stops & S_SIG) {
 			mtx_unlock(&ps->ps_mtx);
@@ -2674,7 +2699,7 @@ issignal(struct thread *td)
 			sigqueue_delete(&p->p_sigqueue, sig);
 			continue;
 		}
-		if (p->p_flag & P_TRACED && (p->p_flag & P_PPTRACE) == 0) {
+		if ((p->p_flag & (P_TRACED | P_PPTRACE)) == P_TRACED) {
 			/*
 			 * If traced, always stop.
 			 * Remove old signal from queue before the stop.
@@ -2772,6 +2797,8 @@ issignal(struct thread *td)
 				mtx_unlock(&ps->ps_mtx);
 				WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK,
 				    &p->p_mtx.lock_object, "Catching SIGSTOP");
+				sigqueue_delete(&td->td_sigqueue, sig);
+				sigqueue_delete(&p->p_sigqueue, sig);
 				p->p_flag |= P_STOPPED_SIG;
 				p->p_xstat = sig;
 				PROC_SLOCK(p);
@@ -2779,7 +2806,7 @@ issignal(struct thread *td)
 				thread_suspend_switch(td, p);
 				PROC_SUNLOCK(p);
 				mtx_lock(&ps->ps_mtx);
-				break;
+				goto next;
 			} else if (prop & SA_IGNORE) {
 				/*
 				 * Except for SIGCONT, shouldn't get here.
@@ -2810,6 +2837,7 @@ issignal(struct thread *td)
 		}
 		sigqueue_delete(&td->td_sigqueue, sig);	/* take the signal! */
 		sigqueue_delete(&p->p_sigqueue, sig);
+next:;
 	}
 	/* NOTREACHED */
 }
diff --git a/sys/kern/sys_process.c b/sys/kern/sys_process.c
index 57b9fb7..c4533ce 100644
--- a/sys/kern/sys_process.c
+++ b/sys/kern/sys_process.c
@@ -648,6 +648,17 @@ sys_ptrace(struct thread *td, struct ptrace_args *uap)
 #define	PROC_WRITE(w, t, a)	proc_write_ ## w (t, a)
 #endif
 
+void
+proc_set_traced(struct proc *p)
+{
+
+	PROC_LOCK_ASSERT(p, MA_OWNED);
+	p->p_flag |= P_TRACED;
+	p->p_flag2 |= P2_PTRACE_FSTP;
+	p->p_ptevents = PTRACE_DEFAULT;
+	p->p_oppid = p->p_pptr->p_pid;
+}
+
 int
 kern_ptrace(struct thread *td, int req, pid_t pid, void *addr, int data)
 {
@@ -856,11 +867,9 @@ kern_ptrace(struct thread *td, int req, pid_t pid, void *addr, int data)
 	switch (req) {
 	case PT_TRACE_ME:
 		/* set my trace flag and "owner" so it can read/write me */
-		p->p_flag |= P_TRACED;
-		p->p_ptevents = PTRACE_DEFAULT;
+		proc_set_traced(p);
 		if (p->p_flag & P_PPWAIT)
 			p->p_flag |= P_PPTRACE;
-		p->p_oppid = p->p_pptr->p_pid;
 		CTR1(KTR_PTRACE, "PT_TRACE_ME: pid %d", p->p_pid);
 		break;
 
@@ -875,9 +884,7 @@ kern_ptrace(struct thread *td, int req, pid_t pid, void *addr, int data)
 		 * The old parent is remembered so we can put things back
 		 * on a "detach".
 		 */
-		p->p_flag |= P_TRACED;
-		p->p_ptevents = PTRACE_DEFAULT;
-		p->p_oppid = p->p_pptr->p_pid;
+		proc_set_traced(p);
 		if (p->p_pptr != td->td_proc) {
 			proc_reparent(p, td->td_proc);
 		}
@@ -1045,6 +1052,17 @@ kern_ptrace(struct thread *td, int req, pid_t pid, void *addr, int data)
 				    p->p_pid, data);
 			p->p_oppid = 0;
 			p->p_ptevents = 0;
+			FOREACH_THREAD_IN_PROC(p, td3) {
+				if ((td3->td_dbgflags & TDB_FSTP) != 0) {
+					sigqueue_delete(&td3->td_sigqueue,
+					    SIGSTOP);
+				}
+				td3->td_dbgflags &= ~(TDB_XSIG | TDB_FSTP);
+			}
+			if ((p->p_flag2 & P2_PTRACE_FSTP) != 0) {
+				sigqueue_delete(&p->p_sigqueue, SIGSTOP);
+				p->p_flag2 &= ~P2_PTRACE_FSTP;
+			}
 
 			/* should we send SIGCHLD? */
 			/* childproc_continued(p); */
@@ -1065,7 +1083,7 @@ kern_ptrace(struct thread *td, int req, pid_t pid, void *addr, int data)
 
 			if (req == PT_DETACH) {
 				FOREACH_THREAD_IN_PROC(p, td3)
-					td3->td_dbgflags &= ~TDB_SUSPEND; 
+					td3->td_dbgflags &= ~TDB_SUSPEND;
 			}
 			/*
 			 * unsuspend all threads, to not let a thread run,
diff --git a/sys/sys/proc.h b/sys/sys/proc.h
index 34e2924..1b8bda5 100644
--- a/sys/sys/proc.h
+++ b/sys/sys/proc.h
@@ -398,6 +398,7 @@ do {									\
 #define	TDB_CHILD	0x00000100 /* New child indicator for ptrace() */
 #define	TDB_BORN	0x00000200 /* New LWP indicator for ptrace() */
 #define	TDB_EXIT	0x00000400 /* Exiting LWP indicator for ptrace() */
+#define	TDB_FSTP	0x00001000 /* The thread is PT_ATTACH leader */
 
 /*
  * "Private" flags kept in td_pflags:
@@ -678,6 +679,7 @@ struct proc {
 #define	P2_NOTRACE	0x00000002	/* No ptrace(2) attach or coredumps. */
 #define	P2_NOTRACE_EXEC 0x00000004	/* Keep P2_NOPTRACE on exec(2). */
 #define	P2_AST_SU	0x00000008	/* Handles SU ast for kthreads. */
+#define	P2_PTRACE_FSTP	0x00000010 /* SIGSTOP from PT_ATTACH not yet handled. */
 
 /* Flags protected by proctree_lock, kept in p_treeflags. */
 #define	P_TREE_ORPHANED		0x00000001	/* Reparented, on orphan list */
@@ -930,6 +932,7 @@ void	proc_linkup(struct proc *p, struct thread *td);
 struct proc *proc_realparent(struct proc *child);
 void	proc_reap(struct thread *td, struct proc *p, int *status, int options);
 void	proc_reparent(struct proc *child, struct proc *newparent);
+void	proc_set_traced(struct proc *p);
 struct	pstats *pstats_alloc(void);
 void	pstats_fork(struct pstats *src, struct pstats *dst);
 void	pstats_free(struct pstats *ps);