uml: stop gdb from deleting breakpoints when running UML

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 find out 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.

[ jdike - checkpatch fixes ]

Signed-off-by: Stanislaw Gruszka <stf_xl@wp.pl>
Signed-off-by: Jeff Dike <jdike@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

4 files changed, 7 insertions, 25 deletions

diff --git a/arch/um/drivers/net_user.c b/arch/um/drivers/net_user.c
index 90d7f2e8ead8..29185cad9fff 100644
--- a/arch/um/drivers/net_user.c
+++ b/arch/um/drivers/net_user.c
@@ -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;
 }
 
diff --git a/arch/um/drivers/slip_user.c b/arch/um/drivers/slip_user.c
index 5f06204d6871..b8711e50da80 100644
--- a/arch/um/drivers/slip_user.c
+++ b/arch/um/drivers/slip_user.c
@@ -77,7 +77,7 @@ static int slip_tramp(char **argv, int fd)
 {
 	struct slip_pre_exec_data pe_data;
 	char *output;
-	int status, pid, fds[2], err, output_len;
+	int pid, fds[2], err, output_len;
 
 	err = os_pipe(fds, 1, 0);
 	if (err < 0) {
@@ -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:
diff --git a/arch/um/drivers/slirp_user.c b/arch/um/drivers/slirp_user.c
index 1865089ff41a..89c1be225fda 100644
--- a/arch/um/drivers/slirp_user.c
+++ b/arch/um/drivers/slirp_user.c
@@ -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;
 }
diff --git a/arch/um/drivers/ubd_user.c b/arch/um/drivers/ubd_user.c
index 41d254bd38df..48fc7452bc1d 100644
--- a/arch/um/drivers/ubd_user.c
+++ b/arch/um/drivers/ubd_user.c
@@ -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);