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Avoid not intended gdb breakpoints removal

PATCH In review Stanislaw Gruszka 2 participants 3 messages Dec 5, 2007 – Dec 6, 2007 User-mode Linux (UML)

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Stanislaw Gruszka

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#0 lore raw

PATCH 1/1 Avoid not intended gdb breakpoints removal

Hi.

Sometimes when UML is debugged gdb miss breakpoints.

When process traced by gdb do fork, debugger remove breakpoints from child address space. There is possibility to trace more than one fork, but this not work with UML, I guess (only guess) there is a deadlock - gdb waits for UML and UML waits for gdb.

When clone() is called with SIGCHLD and CLONE_VM flags, gdb see this as PTRACE_EVENT_FORK not as PTRACE_EVENT_CLONE and remove breakpoints from child and at the same time from traced process, because either have the same address space.

Maybe it is possible to do fix in gdb, but I'm not sure if there is easy way to findout if traced and child processes share memory. So I do fix for UML, it simply do not call clone() with both SIGCHLD and CLONE_VM flags together. Additionally __WALL flag is used for waitpid() to assure not miss clone and normal process events.

Signature · 2 lines
Regards
Stanislaw Gruszka
arch/um/drivers/net_user.c +1 -1
index 90d7f2e..09d497a 100644
@@ -201,7 +201,7 @@ static int change_tramp(char **argv, char *output, int output_len)
 	close(fds[1]);
 
 	if (pid > 0)
-		CATCH_EINTR(err = waitpid(pid, NULL, 0));
+		CATCH_EINTR(err = waitpid(pid, NULL, __WALL));
 	return pid;
 }
arch/um/drivers/port_kern.c +0 -0
arch/um/drivers/slip_user.c +1 -1
index 5f06204..ffc473d 100644
@@ -109,7 +109,7 @@ static int slip_tramp(char **argv, int fd)
 	read_output(fds[0], output, output_len);
 	printk("%s", output);
 
-	CATCH_EINTR(err = waitpid(pid, &status, 0));
+	CATCH_EINTR(err = waitpid(pid, &status, __WALL));
 	if (err < 0)
 		err = errno;
 	else if (!WIFEXITED(status) || (WEXITSTATUS(status) != 0)) {
arch/um/drivers/slirp_user.c +1 -1
index 1865089..f8b0987 100644
@@ -99,7 +99,7 @@ static void slirp_close(int fd, void *data)
 	}
 #endif
 
-	CATCH_EINTR(err = waitpid(pri->pid, &status, WNOHANG));
+	CATCH_EINTR(err = waitpid(pri->pid, &status, WNOHANG | __WALL));
 	if (err < 0) {
 		printk(UM_KERN_ERR "slirp_close: waitpid returned %d\n", errno);
 		return;
arch/um/drivers/ubd_user.c +1 -1
index 41d254b..875b1f3 100644
@@ -49,7 +49,7 @@ int start_io_thread(unsigned long sp, int *fd_out)
 		goto out_close;
 	}
 
-	pid = clone(io_thread, (void *) sp, CLONE_FILES | CLONE_VM | SIGCHLD,
+	pid = clone(io_thread, (void *) sp, CLONE_FILES | CLONE_VM,
 		    NULL);
 	if(pid < 0){
 		err = -errno;
arch/um/drivers/xterm.c +0 -0
arch/um/kernel/reboot.c +0 -0
arch/um/kernel/syscall.c +0 -0
arch/um/os-Linux/aio.c +2 -2
index 4158118..93dc0c8 100644
@@ -218,7 +218,7 @@ static int init_aio_24(void)
 		goto out_close_pipe;
 
 	err = run_helper_thread(not_aio_thread, NULL,
-				CLONE_FILES | CLONE_VM | SIGCHLD, &aio_stack);
+				CLONE_FILES | CLONE_VM, &aio_stack);
 	if (err < 0)
 		goto out_close_pipe;
 

@@ -254,7 +254,7 @@ static int init_aio_26(void)
 	}
 
 	err = run_helper_thread(aio_thread, NULL,
-				CLONE_FILES | CLONE_VM | SIGCHLD, &aio_stack);
+				CLONE_FILES | CLONE_VM, &aio_stack);
 	if (err < 0)
 		return err;
arch/um/os-Linux/drivers/ethertap_user.c +1 -1
index 4ff5536..99d3a50 100644
@@ -132,7 +132,7 @@ static int etap_tramp(char *dev, char *gate, int control_me,
 	if (c != 1) {
 		printk(UM_KERN_ERR "etap_tramp : uml_net failed\n");
 		err = -EINVAL;
-		CATCH_EINTR(n = waitpid(pid, &status, 0));
+		CATCH_EINTR(n = waitpid(pid, &status, __WALL));
 		if (n < 0)
 			err = -errno;
 		else if (!WIFEXITED(status) || (WEXITSTATUS(status) != 1))
arch/um/os-Linux/drivers/tuntap_user.c +1 -1
index 6c55d3c..ff52a58 100644
@@ -107,7 +107,7 @@ static int tuntap_open_tramp(char *gate, int *fd_out, int me, int remote,
 		       "errno = %d\n", errno);
 		return err;
 	}
-	CATCH_EINTR(waitpid(pid, NULL, 0));
+	CATCH_EINTR(waitpid(pid, NULL, __WALL));
 
 	cmsg = CMSG_FIRSTHDR(&msg);
 	if (cmsg == NULL) {
arch/um/os-Linux/helper.c +5 -5
index 7a72dbb..2201b99 100644
@@ -76,7 +76,7 @@ int run_helper(void (*pre_exec)(void *), void *pre_data, char **argv)
 	data.fd = fds[1];
 	data.buf = __cant_sleep() ? kmalloc(PATH_MAX, UM_GFP_ATOMIC) :
 					kmalloc(PATH_MAX, UM_GFP_KERNEL);
-	pid = clone(helper_child, (void *) sp, CLONE_VM | SIGCHLD, &data);
+	pid = clone(helper_child, (void *) sp, CLONE_VM, &data);
 	if (pid < 0) {
 		ret = -errno;
 		printk("run_helper : clone failed, errno = %d\n", errno);

@@ -101,7 +101,7 @@ int run_helper(void (*pre_exec)(void *), void *pre_data, char **argv)
 			ret = n;
 			kill(pid, SIGKILL);
 		}
-		CATCH_EINTR(waitpid(pid, NULL, 0));
+		CATCH_EINTR(waitpid(pid, NULL, __WALL));
 	}
 
 out_free2:

@@ -126,7 +126,7 @@ int run_helper_thread(int (*proc)(void *), void *arg, unsigned int flags,
 		return -ENOMEM;
 
 	sp = stack + UM_KERN_PAGE_SIZE - sizeof(void *);
-	pid = clone(proc, (void *) sp, flags | SIGCHLD, arg);
+	pid = clone(proc, (void *) sp, flags, arg);
 	if (pid < 0) {
 		err = -errno;
 		printk("run_helper_thread : clone failed, errno = %d\n",

@@ -134,7 +134,7 @@ int run_helper_thread(int (*proc)(void *), void *arg, unsigned int flags,
 		return err;
 	}
 	if (stack_out == NULL) {
-		CATCH_EINTR(pid = waitpid(pid, &status, 0));
+		CATCH_EINTR(pid = waitpid(pid, &status, __WALL));
 		if (pid < 0) {
 			err = -errno;
 			printk("run_helper_thread - wait failed, errno = %d\n",

@@ -154,7 +154,7 @@ int helper_wait(int pid)
 {
 	int ret;
 
-	CATCH_EINTR(ret = waitpid(pid, NULL, WNOHANG));
+	CATCH_EINTR(ret = waitpid(pid, NULL, WNOHANG | __WALL));
 	if (ret < 0) {
 		ret = -errno;
 		printk("helper_wait : waitpid failed, errno = %d\n", errno);
arch/um/os-Linux/process.c +2 -2
index 37781db..bda5c31 100644
@@ -101,7 +101,7 @@ void os_kill_process(int pid, int reap_child)
 {
 	kill(pid, SIGKILL);
 	if (reap_child)
-		CATCH_EINTR(waitpid(pid, NULL, 0));
+		CATCH_EINTR(waitpid(pid, NULL, __WALL));
 }
 
 /* This is here uniquely to have access to the userspace errno, i.e. the one

@@ -130,7 +130,7 @@ void os_kill_ptraced_process(int pid, int reap_child)
 	ptrace(PTRACE_KILL, pid);
 	ptrace(PTRACE_CONT, pid);
 	if (reap_child)
-		CATCH_EINTR(waitpid(pid, NULL, 0));
+		CATCH_EINTR(waitpid(pid, NULL, __WALL));
 }
 
 /* Don't use the glibc version, which caches the result in TLS. It misses some
arch/um/os-Linux/sigio.c +0 -0
arch/um/os-Linux/skas/process.c +9 -6
index d77c81d..634fa31 100644
@@ -64,7 +64,7 @@ void wait_stub_done(int pid)
 	int n, status, err;
 
 	while (1) {
-		CATCH_EINTR(n = waitpid(pid, &status, WUNTRACED));
+		CATCH_EINTR(n = waitpid(pid, &status, WUNTRACED | __WALL));
 		if ((n < 0) || !WIFSTOPPED(status))
 			goto bad_wait;
 

@@ -153,7 +153,7 @@ static void handle_trap(int pid, struct uml_pt_regs *regs,
 			panic("handle_trap - continuing to end of syscall "
 			      "failed, errno = %d\n", errno);
 
-		CATCH_EINTR(err = waitpid(pid, &status, WUNTRACED));
+		CATCH_EINTR(err = waitpid(pid, &status, WUNTRACED |__WALL));
 		if ((err < 0) || !WIFSTOPPED(status) ||
 		   (WSTOPSIG(status) != SIGTRAP + 0x80)) {
                         err = ptrace_dump_regs(pid);

@@ -255,16 +255,19 @@ int start_userspace(unsigned long stub_stack)
 		panic("start_userspace : mmap failed, errno = %d", errno);
 	sp = (unsigned long) stack + UM_KERN_PAGE_SIZE - sizeof(void *);
 
-	flags = CLONE_FILES | SIGCHLD;
+	flags = CLONE_FILES;
 	if (proc_mm)
 		flags |= CLONE_VM;
-
+	else {
+		flags |= SIGCHLD;
+	}
+
 	pid = clone(userspace_tramp, (void *) sp, flags, (void *) stub_stack);
 	if (pid < 0)
 		panic("start_userspace : clone failed, errno = %d", errno);
 
 	do {
-		CATCH_EINTR(n = waitpid(pid, &status, WUNTRACED));
+		CATCH_EINTR(n = waitpid(pid, &status, WUNTRACED | __WALL));
 		if (n < 0)
 			panic("start_userspace : wait failed, errno = %d",
 			      errno);

@@ -314,7 +317,7 @@ void userspace(struct uml_pt_regs *regs)
 			      "pid=%d, ptrace operation = %d, errno = %d\n",
 			      pid, op, errno);
 
-		CATCH_EINTR(err = waitpid(pid, &status, WUNTRACED));
+		CATCH_EINTR(err = waitpid(pid, &status, WUNTRACED | __WALL));
 		if (err < 0)
 			panic("userspace - waitpid failed, errno = %d\n",
 			      errno);
arch/um/os-Linux/start_up.c +5 -5
index 7b81f6c..6adebd0 100644
@@ -101,7 +101,7 @@ static int start_ptraced_child(void)
 	else if (pid < 0)
 		fatal_perror("start_ptraced_child : fork failed");
 
-	CATCH_EINTR(n = waitpid(pid, &status, WUNTRACED));
+	CATCH_EINTR(n = waitpid(pid, &status, WUNTRACED | __WALL));
 	if (n < 0)
 		fatal_perror("check_ptrace : waitpid failed");
 	if (!WIFSTOPPED(status) || (WSTOPSIG(status) != SIGSTOP))

@@ -123,7 +123,7 @@ static int stop_ptraced_child(int pid, int exitcode, int mustexit)
 
 	if (ptrace(PTRACE_CONT, pid, 0, 0) < 0)
 		fatal_perror("stop_ptraced_child : ptrace failed");
-	CATCH_EINTR(n = waitpid(pid, &status, 0));
+	CATCH_EINTR(n = waitpid(pid, &status, __WALL));
 	if (!WIFEXITED(status) || (WEXITSTATUS(status) != exitcode)) {
 		int exit_with = WEXITSTATUS(status);
 		if (exit_with == 2)

@@ -198,7 +198,7 @@ static void __init check_sysemu(void)
 	if (ptrace(PTRACE_SYSEMU, pid, 0, 0) < 0)
 		goto fail;
 
-	CATCH_EINTR(n = waitpid(pid, &status, WUNTRACED));
+	CATCH_EINTR(n = waitpid(pid, &status, WUNTRACED | __WALL));
 	if (n < 0)
 		fatal_perror("check_sysemu : wait failed");
 	if (!WIFSTOPPED(status) || (WSTOPSIG(status) != SIGTRAP))

@@ -238,7 +238,7 @@ static void __init check_sysemu(void)
 		count++;
 		if (ptrace(PTRACE_SYSEMU_SINGLESTEP, pid, 0, 0) < 0)
 			goto fail;
-		CATCH_EINTR(n = waitpid(pid, &status, WUNTRACED));
+		CATCH_EINTR(n = waitpid(pid, &status, WUNTRACED | __WALL));
 		if (n < 0)
 			fatal_perror("check_ptrace : wait failed");
 

@@ -291,7 +291,7 @@ static void __init check_ptrace(void)
 		if (ptrace(PTRACE_SYSCALL, pid, 0, 0) < 0)
 			fatal_perror("check_ptrace : ptrace failed");
 
-		CATCH_EINTR(n = waitpid(pid, &status, WUNTRACED));
+		CATCH_EINTR(n = waitpid(pid, &status, WUNTRACED | __WALL));
 		if (n < 0)
 			fatal_perror("check_ptrace : wait failed");
arch/um/os-Linux/util.c +1 -1
index ef09543..3e058ce 100644
@@ -141,7 +141,7 @@ void os_dump_core(void)
 	 * nothing reasonable to do if that fails.
 	 */
 
-	while ((pid = waitpid(-1, NULL, WNOHANG)) > 0)
+	while ((pid = waitpid(-1, NULL, WNOHANG | __WALL)) > 0)
 		os_kill_ptraced_process(pid, 0);
 
 	abort();

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#1 lore raw
Quoted 6 lines · Stanislaw Gruszka

Sometimes when UML is debugged gdb miss breakpoints.

So I do fix for UML,
it simply do not call clone() with both SIGCHLD and CLONE_VM flags together. Additionally __WALL flag is used for waitpid() to assure not miss clone and normal process events.

Woo! You're my favorite person this week[1].

This has bugged me forever, and I was too scared to go into gdb to figure out what its problem was.

A couple of comments:
1 - I think I would prefer to use __WCLONE instead of __WALL since we know what type of process we are creating, and it seems clearer in the code to say specifically what we want

1a - I think I would like to stick all those waits under some API in helper.c as we already have an interface for creating children, and as it stands now, the callers have knowlege about the internal aspects of child creation that they probably shouldn't.

2 - I want to get this into mainline quickly, and I need a
Signed-off-by: from you before it goes anywhere.

Jeff

[1] Narrowly beating out John Reiser, who will be my favorite person of the week that he manages to boot UML under valgrind.

Signature · 11 lines
Work email - jdike at linux dot intel dot com

-------------------------------------------------------------------------
SF.Net email is sponsored by: The Future of Linux Business White Paper
from Novell.  From the desktop to the data center, Linux is going
mainstream.  Let it simplify your IT future.
http://altfarm.mediaplex.com/ad/ck/8857-50307-18918-4
_______________________________________________
User-mode-linux-devel mailing list
[email protected]
https://lists.sourceforge.net/lists/listinfo/user-mode-linux-devel
author
#2 lore raw
Quoted 2 lines · Jeff Dike

This has bugged me forever, and I was too scared to go into gdb to figure out what its problem was.

:-) I considered "debugging a debugger" as something strange but doable.

Quoted 4 lines

A couple of comments:
1 - I think I would prefer to use __WCLONE instead of __WALL since we know what type of process we are creating, and it seems clearer in the code to say specifically what we want

I removed __WALL where possible. Some functions still use it, because must wait for any kind of child.

Quoted 4 lines

1a - I think I would like to stick all those waits under some API in helper.c as we already have an interface for creating children, and as it stands now, the callers have knowlege about the internal aspects of child creation that they probably shouldn't.

Ok, I changed a little helper_wait() function and use it for drivers.

Signed-off-by Stanislaw Gruszka <[email protected]>

---

arch/um/drivers/net_user.c +1 -1
index 90d7f2e..29185ca 100644
@@ -201,7 +201,7 @@ static int change_tramp(char **argv, char *output, int output_len)
 	close(fds[1]);
 
 	if (pid > 0)
-		CATCH_EINTR(err = waitpid(pid, NULL, 0));
+		helper_wait(pid, 0, "change_tramp");
 	return pid;
 }
arch/um/drivers/slip_user.c +1 -9
index 5f06204..a97d942 100644
@@ -109,15 +109,7 @@ static int slip_tramp(char **argv, int fd)
 	read_output(fds[0], output, output_len);
 	printk("%s", output);
 
-	CATCH_EINTR(err = waitpid(pid, &status, 0));
-	if (err < 0)
-		err = errno;
-	else if (!WIFEXITED(status) || (WEXITSTATUS(status) != 0)) {
-		printk(UM_KERN_ERR "'%s' didn't exit with status 0\n", argv[0]);
-		err = -EINVAL;
-	}
-	else err = 0;
-
+	err = helper_wait(pid, 0, argv[0]);
 	close(fds[0]);
 
 out_free:
arch/um/drivers/slirp_user.c +3 -12
index 1865089..89c1be2 100644
@@ -79,7 +79,7 @@ out:
 static void slirp_close(int fd, void *data)
 {
 	struct slirp_data *pri = data;
-	int status,err;
+	int err;
 
 	close(fd);
 	close(pri->slave);

@@ -98,18 +98,9 @@ static void slirp_close(int fd, void *data)
 		       "(%d)\n", pri->pid, errno);
 	}
 #endif
-
-	CATCH_EINTR(err = waitpid(pri->pid, &status, WNOHANG));
-	if (err < 0) {
-		printk(UM_KERN_ERR "slirp_close: waitpid returned %d\n", errno);
-		return;
-	}
-
-	if (err == 0) {
-		printk(UM_KERN_ERR "slirp_close: process %d has not exited\n",
-		       pri->pid);
+	err = helper_wait(pri->pid, 1, "slirp_close");
+	if (err < 0)
 		return;
-	}
 
 	pri->pid = -1;
 }
arch/um/drivers/ubd_kern.c +0 -0
arch/um/drivers/ubd_user.c +1 -2
index 41d254b..48fc745 100644
@@ -49,8 +49,7 @@ int start_io_thread(unsigned long sp, int *fd_out)
 		goto out_close;
 	}
 
-	pid = clone(io_thread, (void *) sp, CLONE_FILES | CLONE_VM | SIGCHLD,
-		    NULL);
+	pid = clone(io_thread, (void *) sp, CLONE_FILES | CLONE_VM, NULL);
 	if(pid < 0){
 		err = -errno;
 		printk("start_io_thread - clone failed : errno = %d\n", errno);
arch/um/include/os.h +1 -1
index fbf0a87..6f0d1c7 100644
@@ -214,7 +214,7 @@ extern int execvp_noalloc(char *buf, const char *file, char *const argv[]);
 extern int run_helper(void (*pre_exec)(void *), void *pre_data, char **argv);
 extern int run_helper_thread(int (*proc)(void *), void *arg,
 			     unsigned int flags, unsigned long *stack_out);
-extern int helper_wait(int pid);
+extern int helper_wait(int pid, int nohang, char *pname);
 
 
 /* tls.c */
arch/um/os-Linux/aio.c +2 -2
index 4158118..93dc0c8 100644
@@ -218,7 +218,7 @@ static int init_aio_24(void)
 		goto out_close_pipe;
 
 	err = run_helper_thread(not_aio_thread, NULL,
-				CLONE_FILES | CLONE_VM | SIGCHLD, &aio_stack);
+				CLONE_FILES | CLONE_VM, &aio_stack);
 	if (err < 0)
 		goto out_close_pipe;
 

@@ -254,7 +254,7 @@ static int init_aio_26(void)
 	}
 
 	err = run_helper_thread(aio_thread, NULL,
-				CLONE_FILES | CLONE_VM | SIGCHLD, &aio_stack);
+				CLONE_FILES | CLONE_VM, &aio_stack);
 	if (err < 0)
 		return err;
arch/um/os-Linux/drivers/ethertap_user.c +2 -8
index 4ff5536..07ca0cb 100644
@@ -94,7 +94,7 @@ static int etap_tramp(char *dev, char *gate, int control_me,
 		      int control_remote, int data_me, int data_remote)
 {
 	struct etap_pre_exec_data pe_data;
-	int pid, status, err, n;
+	int pid, err, n;
 	char version_buf[sizeof("nnnnn\0")];
 	char data_fd_buf[sizeof("nnnnnn\0")];
 	char gate_buf[sizeof("nnn.nnn.nnn.nnn\0")];

@@ -131,13 +131,7 @@ static int etap_tramp(char *dev, char *gate, int control_me,
 	}
 	if (c != 1) {
 		printk(UM_KERN_ERR "etap_tramp : uml_net failed\n");
-		err = -EINVAL;
-		CATCH_EINTR(n = waitpid(pid, &status, 0));
-		if (n < 0)
-			err = -errno;
-		else if (!WIFEXITED(status) || (WEXITSTATUS(status) != 1))
-			printk(UM_KERN_ERR "uml_net didn't exit with "
-			       "status 1\n");
+		err = helper_wait(pid, 0, "uml_net");
 	}
 	return err;
 }
arch/um/os-Linux/drivers/tuntap_user.c +1 -1
index 6c55d3c..7b38289 100644
@@ -107,7 +107,7 @@ static int tuntap_open_tramp(char *gate, int *fd_out, int me, int remote,
 		       "errno = %d\n", errno);
 		return err;
 	}
-	CATCH_EINTR(waitpid(pid, NULL, 0));
+	helper_wait(pid, 0, "tuntap_open_tramp");
 
 	cmsg = CMSG_FIRSTHDR(&msg);
 	if (cmsg == NULL) {
arch/um/os-Linux/helper.c +26 -11
index 7a72dbb..813b15d 100644
@@ -76,7 +76,7 @@ int run_helper(void (*pre_exec)(void *), void *pre_data, char **argv)
 	data.fd = fds[1];
 	data.buf = __cant_sleep() ? kmalloc(PATH_MAX, UM_GFP_ATOMIC) :
 					kmalloc(PATH_MAX, UM_GFP_KERNEL);
-	pid = clone(helper_child, (void *) sp, CLONE_VM | SIGCHLD, &data);
+	pid = clone(helper_child, (void *) sp, CLONE_VM, &data);
 	if (pid < 0) {
 		ret = -errno;
 		printk("run_helper : clone failed, errno = %d\n", errno);

@@ -101,7 +101,7 @@ int run_helper(void (*pre_exec)(void *), void *pre_data, char **argv)
 			ret = n;
 			kill(pid, SIGKILL);
 		}
-		CATCH_EINTR(waitpid(pid, NULL, 0));
+		CATCH_EINTR(waitpid(pid, NULL, __WCLONE));
 	}
 
 out_free2:

@@ -126,7 +126,7 @@ int run_helper_thread(int (*proc)(void *), void *arg, unsigned int flags,
 		return -ENOMEM;
 
 	sp = stack + UM_KERN_PAGE_SIZE - sizeof(void *);
-	pid = clone(proc, (void *) sp, flags | SIGCHLD, arg);
+	pid = clone(proc, (void *) sp, flags, arg);
 	if (pid < 0) {
 		err = -errno;
 		printk("run_helper_thread : clone failed, errno = %d\n",

@@ -134,7 +134,7 @@ int run_helper_thread(int (*proc)(void *), void *arg, unsigned int flags,
 		return err;
 	}
 	if (stack_out == NULL) {
-		CATCH_EINTR(pid = waitpid(pid, &status, 0));
+		CATCH_EINTR(pid = waitpid(pid, &status, __WCLONE));
 		if (pid < 0) {
 			err = -errno;
 			printk("run_helper_thread - wait failed, errno = %d\n",

@@ -150,14 +150,29 @@ int run_helper_thread(int (*proc)(void *), void *arg, unsigned int flags,
 	return pid;
 }
 
-int helper_wait(int pid)
+int helper_wait(int pid, int nohang, char *pname)
 {
-	int ret;
+	int ret, status;
+	int wflags = __WCLONE;
 
-	CATCH_EINTR(ret = waitpid(pid, NULL, WNOHANG));
+	if (nohang)
+		wflags |= WNOHANG;
+
+	if (!pname)
+		pname = "helper_wait";
+
+	CATCH_EINTR(ret = waitpid(pid, &status, wflags));
 	if (ret < 0) {
-		ret = -errno;
-		printk("helper_wait : waitpid failed, errno = %d\n", errno);
-	}
-	return ret;
+		printk("%s : waitpid process %d failed, errno = %d\n",
+		        pname, pid, errno);
+		return -errno;
+	} else if (nohang && ret == 0) {
+		printk("%s : process %d has not exited\n", pname, pid);
+		return -ECHILD;
+	} else if (!WIFEXITED(status) || WEXITSTATUS(status) != 0) {
+		printk(UM_KERN_ERR "%s : process %d didn't exit with status 0\n",
+		       pname, pid);
+		return -ECHILD;
+	} else
+		return 0;
 }
arch/um/os-Linux/process.c +2 -2
index 37781db..bda5c31 100644
@@ -101,7 +101,7 @@ void os_kill_process(int pid, int reap_child)
 {
 	kill(pid, SIGKILL);
 	if (reap_child)
-		CATCH_EINTR(waitpid(pid, NULL, 0));
+		CATCH_EINTR(waitpid(pid, NULL, __WALL));
 }
 
 /* This is here uniquely to have access to the userspace errno, i.e. the one

@@ -130,7 +130,7 @@ void os_kill_ptraced_process(int pid, int reap_child)
 	ptrace(PTRACE_KILL, pid);
 	ptrace(PTRACE_CONT, pid);
 	if (reap_child)
-		CATCH_EINTR(waitpid(pid, NULL, 0));
+		CATCH_EINTR(waitpid(pid, NULL, __WALL));
 }
 
 /* Don't use the glibc version, which caches the result in TLS. It misses some
arch/um/os-Linux/skas/process.c +7 -5
index d77c81d..e8b7a97 100644
@@ -64,7 +64,7 @@ void wait_stub_done(int pid)
 	int n, status, err;
 
 	while (1) {
-		CATCH_EINTR(n = waitpid(pid, &status, WUNTRACED));
+		CATCH_EINTR(n = waitpid(pid, &status, WUNTRACED | __WALL));
 		if ((n < 0) || !WIFSTOPPED(status))
 			goto bad_wait;
 

@@ -153,7 +153,7 @@ static void handle_trap(int pid, struct uml_pt_regs *regs,
 			panic("handle_trap - continuing to end of syscall "
 			      "failed, errno = %d\n", errno);
 
-		CATCH_EINTR(err = waitpid(pid, &status, WUNTRACED));
+		CATCH_EINTR(err = waitpid(pid, &status, WUNTRACED | __WALL));
 		if ((err < 0) || !WIFSTOPPED(status) ||
 		   (WSTOPSIG(status) != SIGTRAP + 0x80)) {
                         err = ptrace_dump_regs(pid);

@@ -255,16 +255,18 @@ int start_userspace(unsigned long stub_stack)
 		panic("start_userspace : mmap failed, errno = %d", errno);
 	sp = (unsigned long) stack + UM_KERN_PAGE_SIZE - sizeof(void *);
 
-	flags = CLONE_FILES | SIGCHLD;
+	flags = CLONE_FILES;
 	if (proc_mm)
 		flags |= CLONE_VM;
+	else
+		flags |= SIGCHLD;
 
 	pid = clone(userspace_tramp, (void *) sp, flags, (void *) stub_stack);
 	if (pid < 0)
 		panic("start_userspace : clone failed, errno = %d", errno);
 
 	do {
-		CATCH_EINTR(n = waitpid(pid, &status, WUNTRACED));
+		CATCH_EINTR(n = waitpid(pid, &status, WUNTRACED | __WALL));
 		if (n < 0)
 			panic("start_userspace : wait failed, errno = %d",
 			      errno);

@@ -314,7 +316,7 @@ void userspace(struct uml_pt_regs *regs)
 			      "pid=%d, ptrace operation = %d, errno = %d\n",
 			      pid, op, errno);
 
-		CATCH_EINTR(err = waitpid(pid, &status, WUNTRACED));
+		CATCH_EINTR(err = waitpid(pid, &status, WUNTRACED | __WALL));
 		if (err < 0)
 			panic("userspace - waitpid failed, errno = %d\n",
 			      errno);
arch/um/os-Linux/start_up.c +0 -0
arch/um/os-Linux/util.c +1 -1
index ef09543..3e058ce 100644
@@ -141,7 +141,7 @@ void os_dump_core(void)
 	 * nothing reasonable to do if that fails.
 	 */
 
-	while ((pid = waitpid(-1, NULL, WNOHANG)) > 0)
+	while ((pid = waitpid(-1, NULL, WNOHANG | __WALL)) > 0)
 		os_kill_ptraced_process(pid, 0);
 
 	abort();

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