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>

7 files changed, 42 insertions, 30 deletions

diff --git a/arch/um/os-Linux/aio.c b/arch/um/os-Linux/aio.c
index 4158118..93dc0c8 100644
--- a/arch/um/os-Linux/aio.c
+++ b/arch/um/os-Linux/aio.c
@@ -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;
 
diff --git a/arch/um/os-Linux/drivers/ethertap_user.c b/arch/um/os-Linux/drivers/ethertap_user.c
index 4ff5536..07ca0cb 100644
--- a/arch/um/os-Linux/drivers/ethertap_user.c
+++ b/arch/um/os-Linux/drivers/ethertap_user.c
@@ -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;
 }
diff --git a/arch/um/os-Linux/drivers/tuntap_user.c b/arch/um/os-Linux/drivers/tuntap_user.c
index 6c55d3c..1037a3b6 100644
--- a/arch/um/os-Linux/drivers/tuntap_user.c
+++ b/arch/um/os-Linux/drivers/tuntap_user.c
@@ -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) {
diff --git a/arch/um/os-Linux/helper.c b/arch/um/os-Linux/helper.c
index 7a72dbb..fba3f0f 100644
--- a/arch/um/os-Linux/helper.c
+++ b/arch/um/os-Linux/helper.c
@@ -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 +150,30 @@ 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(UM_KERN_ERR "%s : waitpid process %d failed, "
+		       "errno = %d\n", pname, pid, errno);
+		return -errno;
+	} else if (nohang && ret == 0) {
+		printk(UM_KERN_ERR "%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;
 }
diff --git a/arch/um/os-Linux/process.c b/arch/um/os-Linux/process.c
index 37781db..bda5c31 100644
--- a/arch/um/os-Linux/process.c
+++ b/arch/um/os-Linux/process.c
@@ -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
diff --git a/arch/um/os-Linux/skas/process.c b/arch/um/os-Linux/skas/process.c
index d77c81d..e8b7a97 100644
--- a/arch/um/os-Linux/skas/process.c
+++ b/arch/um/os-Linux/skas/process.c
@@ -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);
diff --git a/arch/um/os-Linux/util.c b/arch/um/os-Linux/util.c
index ef09543..3e058ce 100644
--- a/arch/um/os-Linux/util.c
+++ b/arch/um/os-Linux/util.c
@@ -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();