[PATCH v1 0/2] pidfd: waiting on processes through pidfds

[PATCH v1 0/2] pidfd: waiting on processes through pidfds

[Christian Brauner]

Hey everyone,

/* v1 */
This adds the ability to wait on processes using pidfds. This is one of
the few missing pieces to make it possible to manage processes using
only pidfds.

Please note the following major changes (More details can be found in
the individual commit changelogs.):
- Add the new type P_PIDFD to waitid() instead of a new dedicated
  pidfd_wait() syscall.
  This is the same approach we discussed a few months ago and still
  prefer over adding a dedicated syscall.
- Adapt the tests to the new type P_PIDFD for waitid().
- Remove struct waitid_info patch.
  This will be sent out as a separate patch.
- Remove CLONE_WAIT_PID patch.
  This will be sent out as a separate patch.

The core patch for waitid is pleasantly small. The largest change is
caused by adding proper tests for waitid(P_PIDFD).

/* v0 */
Link: https://lore.kernel.org/lkml/20190724144651.28272-1-christian@brauner.io

Thanks!
Christian

Christian Brauner (2):
  pidfd: add P_PIDFD to waitid()
  pidfd: add pidfd_wait tests

 include/linux/pid.h                        |   4 +
 include/uapi/linux/wait.h                  |   1 +
 kernel/exit.c                              |  25 ++-
 kernel/fork.c                              |   8 +
 kernel/signal.c                            |   7 +-
 tools/testing/selftests/pidfd/pidfd.h      |  25 +++
 tools/testing/selftests/pidfd/pidfd_test.c |  14 --
 tools/testing/selftests/pidfd/pidfd_wait.c | 245 +++++++++++++++++++++
 8 files changed, 311 insertions(+), 18 deletions(-)
 create mode 100644 tools/testing/selftests/pidfd/pidfd_wait.c

-- 
2.22.0

[PATCH v1 1/2] pidfd: add P_PIDFD to waitid()

[Christian Brauner]

This adds the P_PIDFD type to waitid().
One of the last remaining bits for the pidfd api is to make it possible
to wait on pidfds. With P_PIDFD added to waitid() the parts of userspace
that want to use the pidfd api to exclusively manage processes can do so
now.

One of the things this will unblock in the future is the ability to make
it possible to retrieve the exit status via waitid(P_PIDFD) for
non-parent processes if handed a _suitable_ pidfd that has this feature
set. This is similar to what you can do on FreeBSD with kqueue(). It
might even end up being possible to wait on a process as a non-parent if
an appropriate property is enabled on the pidfd.

With P_PIDFD no scoping of the process identified by the pidfd is
possible, i.e. it explicitly blocks things such as wait4(-1), wait4(0),
waitid(P_ALL), waitid(P_PGID) etc. It only allows for semantics
equivalent to wait4(pid), waitid(P_PID). Users that need scoping should
rely on pid-based wait*() syscalls for now.

Signed-off-by: Christian Brauner <christian@brauner.io>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Joel Fernandes (Google) <joel@joelfernandes.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: David Howells <dhowells@redhat.com>
Cc: Jann Horn <jannh@google.com>
Cc: Andy Lutomirsky <luto@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Aleksa Sarai <cyphar@cyphar.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
---
v1:
- Linus Torvalds <torvalds@linux-foundation.org>:
  - use flag as discussed before, not a dedicated pidfd_wait() syscall
- Oleg Nesterov <oleg@redhat.com>:
  - use flag as discussed before, not a dedicated pidfd_wait() syscall
---
 include/linux/pid.h       |  4 ++++
 include/uapi/linux/wait.h |  1 +
 kernel/exit.c             | 25 +++++++++++++++++++++++--
 kernel/fork.c             |  8 ++++++++
 kernel/signal.c           |  7 +++++--
 5 files changed, 41 insertions(+), 4 deletions(-)

diff --git a/include/linux/pid.h b/include/linux/pid.h
index 2a83e434db9d..9645b1194c98 100644
--- a/include/linux/pid.h
+++ b/include/linux/pid.h
@@ -72,6 +72,10 @@ extern struct pid init_struct_pid;
 
 extern const struct file_operations pidfd_fops;
 
+struct file;
+
+extern struct pid *pidfd_pid(const struct file *file);
+
 static inline struct pid *get_pid(struct pid *pid)
 {
 	if (pid)
diff --git a/include/uapi/linux/wait.h b/include/uapi/linux/wait.h
index ac49a220cf2a..85b809fc9f11 100644
--- a/include/uapi/linux/wait.h
+++ b/include/uapi/linux/wait.h
@@ -17,6 +17,7 @@
 #define P_ALL		0
 #define P_PID		1
 #define P_PGID		2
+#define P_PIDFD		3
 
 
 #endif /* _UAPI_LINUX_WAIT_H */
diff --git a/kernel/exit.c b/kernel/exit.c
index a75b6a7f458a..a9b49260b965 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -1555,6 +1555,7 @@ static long do_wait(struct wait_opts *wo)
 static long kernel_waitid(int which, pid_t upid, struct waitid_info *infop,
 			  int options, struct rusage *ru)
 {
+	struct fd f;
 	struct wait_opts wo;
 	struct pid *pid = NULL;
 	enum pid_type type;
@@ -1580,11 +1581,27 @@ static long kernel_waitid(int which, pid_t upid, struct waitid_info *infop,
 		if (upid <= 0)
 			return -EINVAL;
 		break;
+	case P_PIDFD:
+		type = PIDTYPE_PID;
+		if (upid < 0)
+			return -EINVAL;
+
+		f = fdget(upid);
+		if (!f.file)
+			return -EBADF;
+
+		pid = pidfd_pid(f.file);
+		if (IS_ERR(pid)) {
+			fdput(f);
+			return PTR_ERR(pid);
+		}
+
+		break;
 	default:
 		return -EINVAL;
 	}
 
-	if (type < PIDTYPE_MAX)
+	if (type < PIDTYPE_MAX && !pid)
 		pid = find_get_pid(upid);
 
 	wo.wo_type	= type;
@@ -1594,7 +1611,11 @@ static long kernel_waitid(int which, pid_t upid, struct waitid_info *infop,
 	wo.wo_rusage	= ru;
 	ret = do_wait(&wo);
 
-	put_pid(pid);
+	if (which == P_PIDFD)
+		fdput(f);
+	else
+		put_pid(pid);
+
 	return ret;
 }
 
diff --git a/kernel/fork.c b/kernel/fork.c
index d8ae0f1b4148..b169e2ca2d84 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1690,6 +1690,14 @@ static inline void rcu_copy_process(struct task_struct *p)
 #endif /* #ifdef CONFIG_TASKS_RCU */
 }
 
+struct pid *pidfd_pid(const struct file *file)
+{
+	if (file->f_op == &pidfd_fops)
+		return file->private_data;
+
+	return ERR_PTR(-EBADF);
+}
+
 static int pidfd_release(struct inode *inode, struct file *file)
 {
 	struct pid *pid = file->private_data;
diff --git a/kernel/signal.c b/kernel/signal.c
index 91b789dd6e72..2e567f64812f 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -3672,8 +3672,11 @@ static int copy_siginfo_from_user_any(kernel_siginfo_t *kinfo, siginfo_t *info)
 
 static struct pid *pidfd_to_pid(const struct file *file)
 {
-	if (file->f_op == &pidfd_fops)
-		return file->private_data;
+	struct pid *pid;
+
+	pid = pidfd_pid(file);
+	if (!IS_ERR(pid))
+		return pid;
 
 	return tgid_pidfd_to_pid(file);
 }
-- 
2.22.0

[PATCH v1 2/2] pidfd: add pidfd_wait tests

[Christian Brauner]

Add tests for pidfd_wait() and CLONE_WAIT_PID:
- test that waitid(P_PIDFD) can wait on a pidfd
- test that waitid(P_PIDFD) can wait on a pidfd and return siginfo_t
- test that waitid(P_PIDFD) works with WEXITED
- test that waitid(P_PIDFD) works with WSTOPPED
- test that waitid(P_PIDFD) works with WUNTRACED
- test that waitid(P_PIDFD) works with WCONTINUED
- test that waitid(P_PIDFD) works with WNOWAIT
- test that waitid(P_PIDFD)works with WNOHANG

Signed-off-by: Christian Brauner <christian@brauner.io>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Joel Fernandes (Google) <joel@joelfernandes.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: David Howells <dhowells@redhat.com>
Cc: Jann Horn <jannh@google.com>
Cc: Andy Lutomirsky <luto@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Aleksa Sarai <cyphar@cyphar.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
---
v1:
- Christian Brauner <christian@brauner.io>:
  - adapt tests to new P_PIDFD concept
---
 tools/testing/selftests/pidfd/pidfd.h      |  25 +++
 tools/testing/selftests/pidfd/pidfd_test.c |  14 --
 tools/testing/selftests/pidfd/pidfd_wait.c | 245 +++++++++++++++++++++
 3 files changed, 270 insertions(+), 14 deletions(-)
 create mode 100644 tools/testing/selftests/pidfd/pidfd_wait.c

diff --git a/tools/testing/selftests/pidfd/pidfd.h b/tools/testing/selftests/pidfd/pidfd.h
index 8452e910463f..7d7d0ca05e0b 100644
--- a/tools/testing/selftests/pidfd/pidfd.h
+++ b/tools/testing/selftests/pidfd/pidfd.h
@@ -16,6 +16,26 @@
 
 #include "../kselftest.h"
 
+#ifndef P_PIDFD
+#define P_PIDFD 3
+#endif
+
+#ifndef CLONE_PIDFD
+#define CLONE_PIDFD 0x00001000
+#endif
+
+#ifndef __NR_pidfd_open
+#define __NR_pidfd_open -1
+#endif
+
+#ifndef __NR_pidfd_send_signal
+#define __NR_pidfd_send_signal -1
+#endif
+
+#ifndef __NR_clone3
+#define __NR_clone3 -1
+#endif
+
 /*
  * The kernel reserves 300 pids via RESERVED_PIDS in kernel/pid.c
  * That means, when it wraps around any pid < 300 will be skipped.
@@ -53,5 +73,10 @@ int wait_for_pid(pid_t pid)
 	return WEXITSTATUS(status);
 }
 
+static inline int sys_pidfd_send_signal(int pidfd, int sig, siginfo_t *info,
+					unsigned int flags)
+{
+	return syscall(__NR_pidfd_send_signal, pidfd, sig, info, flags);
+}
 
 #endif /* __PIDFD_H */
diff --git a/tools/testing/selftests/pidfd/pidfd_test.c b/tools/testing/selftests/pidfd/pidfd_test.c
index 7eaa8a3de262..42e3eb494d72 100644
--- a/tools/testing/selftests/pidfd/pidfd_test.c
+++ b/tools/testing/selftests/pidfd/pidfd_test.c
@@ -21,20 +21,12 @@
 #include "pidfd.h"
 #include "../kselftest.h"
 
-#ifndef __NR_pidfd_send_signal
-#define __NR_pidfd_send_signal -1
-#endif
-
 #define str(s) _str(s)
 #define _str(s) #s
 #define CHILD_THREAD_MIN_WAIT 3 /* seconds */
 
 #define MAX_EVENTS 5
 
-#ifndef CLONE_PIDFD
-#define CLONE_PIDFD 0x00001000
-#endif
-
 static pid_t pidfd_clone(int flags, int *pidfd, int (*fn)(void *))
 {
 	size_t stack_size = 1024;
@@ -47,12 +39,6 @@ static pid_t pidfd_clone(int flags, int *pidfd, int (*fn)(void *))
 #endif
 }
 
-static inline int sys_pidfd_send_signal(int pidfd, int sig, siginfo_t *info,
-					unsigned int flags)
-{
-	return syscall(__NR_pidfd_send_signal, pidfd, sig, info, flags);
-}
-
 static int signal_received;
 
 static void set_signal_received_on_sigusr1(int sig)
diff --git a/tools/testing/selftests/pidfd/pidfd_wait.c b/tools/testing/selftests/pidfd/pidfd_wait.c
new file mode 100644
index 000000000000..018d806032c0
--- /dev/null
+++ b/tools/testing/selftests/pidfd/pidfd_wait.c
@@ -0,0 +1,245 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#define _GNU_SOURCE
+#include <errno.h>
+#include <linux/sched.h>
+#include <linux/types.h>
+#include <signal.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sched.h>
+#include <string.h>
+#include <sys/resource.h>
+#include <sys/time.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+#include "pidfd.h"
+#include "../kselftest.h"
+
+#define ptr_to_u64(ptr) ((__u64)((uintptr_t)(ptr)))
+
+static pid_t sys_clone3(struct clone_args *args)
+{
+	return syscall(__NR_clone3, args, sizeof(struct clone_args));
+}
+
+static int sys_waitid(int which, pid_t pid, siginfo_t *info, int options,
+		      struct rusage *ru)
+{
+	return syscall(__NR_waitid, which, pid, info, options, ru);
+}
+
+static int test_pidfd_wait_simple(void)
+{
+	const char *test_name = "pidfd wait siginfo";
+	int pidfd = -1, status = 0;
+	pid_t parent_tid = -1;
+	struct clone_args args = {
+		.parent_tid = ptr_to_u64(&parent_tid),
+		.pidfd = ptr_to_u64(&pidfd),
+		.flags = CLONE_PIDFD | CLONE_PARENT_SETTID,
+		.exit_signal = SIGCHLD,
+	};
+	int ret;
+	pid_t pid;
+	siginfo_t info = {
+		.si_signo = 0,
+	};
+
+	pid = sys_clone3(&args);
+	if (pid < 0)
+		ksft_exit_fail_msg("%s test: failed to create new process %s\n",
+				   test_name, strerror(errno));
+
+	if (pid == 0)
+		exit(EXIT_SUCCESS);
+
+	pid = sys_waitid(P_PIDFD, pidfd, &info, WEXITED, NULL);
+	if (pid < 0)
+		ksft_exit_fail_msg(
+			"%s test: failed to wait on process with pid %d and pidfd %d: %s\n",
+			test_name, parent_tid, pidfd, strerror(errno));
+
+	if (!WIFEXITED(info.si_status) || WEXITSTATUS(info.si_status))
+		ksft_exit_fail_msg(
+			"%s test: unexpected status received after waiting on process with pid %d and pidfd %d: %s\n",
+			test_name, parent_tid, pidfd, strerror(errno));
+	close(pidfd);
+
+	if (info.si_signo != SIGCHLD)
+		ksft_exit_fail_msg(
+			"%s test: unexpected si_signo value %d received after waiting on process with pid %d and pidfd %d: %s\n",
+			test_name, info.si_signo, parent_tid, pidfd,
+			strerror(errno));
+
+	if (info.si_code != CLD_EXITED)
+		ksft_exit_fail_msg(
+			"%s test: unexpected si_code value %d received after waiting on process with pid %d and pidfd %d: %s\n",
+			test_name, info.si_code, parent_tid, pidfd,
+			strerror(errno));
+
+	if (info.si_pid != parent_tid)
+		ksft_exit_fail_msg(
+			"%s test: unexpected si_pid value %d received after waiting on process with pid %d and pidfd %d: %s\n",
+			test_name, info.si_pid, parent_tid, pidfd,
+			strerror(errno));
+
+	ksft_test_result_pass("%s test: Passed\n", test_name);
+	return 0;
+}
+
+static int test_pidfd_wait_states(void)
+{
+	const char *test_name = "pidfd wait states";
+	int pidfd = -1, status = 0;
+	pid_t parent_tid = -1;
+	struct clone_args args = {
+		.parent_tid = ptr_to_u64(&parent_tid),
+		.pidfd = ptr_to_u64(&pidfd),
+		.flags = CLONE_PIDFD | CLONE_PARENT_SETTID,
+		.exit_signal = SIGCHLD,
+	};
+	int ret;
+	pid_t pid;
+	siginfo_t info = {
+		.si_signo = 0,
+	};
+
+	pid = sys_clone3(&args);
+	if (pid < 0)
+		ksft_exit_fail_msg("%s test: failed to create new process %s\n",
+				   test_name, strerror(errno));
+
+	if (pid == 0) {
+		kill(getpid(), SIGSTOP);
+		kill(getpid(), SIGSTOP);
+		exit(EXIT_SUCCESS);
+	}
+
+	ret = sys_waitid(P_PIDFD, pidfd, &info, WSTOPPED, NULL);
+	if (ret < 0)
+		ksft_exit_fail_msg(
+			"%s test: failed to wait on process with pid %d and pidfd %d: %s\n",
+			test_name, parent_tid, pidfd, strerror(errno));
+
+	if (info.si_signo != SIGCHLD)
+		ksft_exit_fail_msg(
+			"%s test: unexpected si_signo value %d received after waiting on process with pid %d and pidfd %d: %s\n",
+			test_name, info.si_signo, parent_tid, pidfd,
+			strerror(errno));
+
+	if (info.si_code != CLD_STOPPED)
+		ksft_exit_fail_msg(
+			"%s test: unexpected si_code value %d received after waiting on process with pid %d and pidfd %d: %s\n",
+			test_name, info.si_code, parent_tid, pidfd,
+			strerror(errno));
+
+	if (info.si_pid != parent_tid)
+		ksft_exit_fail_msg(
+			"%s test: unexpected si_pid value %d received after waiting on process with pid %d and pidfd %d: %s\n",
+			test_name, info.si_pid, parent_tid, pidfd,
+			strerror(errno));
+
+	ret = sys_pidfd_send_signal(pidfd, SIGCONT, NULL, 0);
+	if (ret < 0)
+		ksft_exit_fail_msg(
+			"%s test: failed to wait on process with pid %d and pidfd %d: %s\n",
+			test_name, parent_tid, pidfd, strerror(errno));
+
+	ret = sys_waitid(P_PIDFD, pidfd, &info, WCONTINUED, NULL);
+	if (ret < 0)
+		ksft_exit_fail_msg(
+			"%s test: failed to wait on process with pid %d and pidfd %d: %s\n",
+			test_name, parent_tid, pidfd, strerror(errno));
+
+	if (info.si_signo != SIGCHLD)
+		ksft_exit_fail_msg(
+			"%s test: unexpected si_signo value %d received after waiting on process with pid %d and pidfd %d: %s\n",
+			test_name, info.si_signo, parent_tid, pidfd,
+			strerror(errno));
+
+	if (info.si_code != CLD_CONTINUED)
+		ksft_exit_fail_msg(
+			"%s test: unexpected si_code value %d received after waiting on process with pid %d and pidfd %d: %s\n",
+			test_name, info.si_code, parent_tid, pidfd,
+			strerror(errno));
+
+	if (info.si_pid != parent_tid)
+		ksft_exit_fail_msg(
+			"%s test: unexpected si_pid value %d received after waiting on process with pid %d and pidfd %d: %s\n",
+			test_name, info.si_pid, parent_tid, pidfd,
+			strerror(errno));
+
+	ret = sys_waitid(P_PIDFD, pidfd, &info, WUNTRACED, NULL);
+	if (ret < 0)
+		ksft_exit_fail_msg(
+			"%s test: failed to wait on process with pid %d and pidfd %d: %s\n",
+			test_name, parent_tid, pidfd, strerror(errno));
+
+	if (info.si_signo != SIGCHLD)
+		ksft_exit_fail_msg(
+			"%s test: unexpected si_signo value %d received after waiting on process with pid %d and pidfd %d: %s\n",
+			test_name, info.si_signo, parent_tid, pidfd,
+			strerror(errno));
+
+	if (info.si_code != CLD_STOPPED)
+		ksft_exit_fail_msg(
+			"%s test: unexpected si_code value %d received after waiting on process with pid %d and pidfd %d: %s\n",
+			test_name, info.si_code, parent_tid, pidfd,
+			strerror(errno));
+
+	if (info.si_pid != parent_tid)
+		ksft_exit_fail_msg(
+			"%s test: unexpected si_pid value %d received after waiting on process with pid %d and pidfd %d: %s\n",
+			test_name, info.si_pid, parent_tid, pidfd,
+			strerror(errno));
+
+	ret = sys_pidfd_send_signal(pidfd, SIGKILL, NULL, 0);
+	if (ret < 0)
+		ksft_exit_fail_msg(
+			"%s test: failed to wait on process with pid %d and pidfd %d: %s\n",
+			test_name, parent_tid, pidfd, strerror(errno));
+
+	ret = sys_waitid(P_PIDFD, pidfd, &info, WEXITED, NULL);
+	if (ret < 0)
+		ksft_exit_fail_msg(
+			"%s test: failed to wait on process with pid %d and pidfd %d: %s\n",
+			test_name, parent_tid, pidfd, strerror(errno));
+
+	if (info.si_signo != SIGCHLD)
+		ksft_exit_fail_msg(
+			"%s test: unexpected si_signo value %d received after waiting on process with pid %d and pidfd %d: %s\n",
+			test_name, info.si_signo, parent_tid, pidfd,
+			strerror(errno));
+
+	if (info.si_code != CLD_KILLED)
+		ksft_exit_fail_msg(
+			"%s test: unexpected si_code value %d received after waiting on process with pid %d and pidfd %d: %s\n",
+			test_name, info.si_code, parent_tid, pidfd,
+			strerror(errno));
+
+	if (info.si_pid != parent_tid)
+		ksft_exit_fail_msg(
+			"%s test: unexpected si_pid value %d received after waiting on process with pid %d and pidfd %d: %s\n",
+			test_name, info.si_pid, parent_tid, pidfd,
+			strerror(errno));
+
+	close(pidfd);
+
+	ksft_test_result_pass("%s test: Passed\n", test_name);
+	return 0;
+}
+
+int main(int argc, char **argv)
+{
+	ksft_print_header();
+	ksft_set_plan(2);
+
+	test_pidfd_wait_simple();
+	test_pidfd_wait_states();
+
+	return ksft_exit_pass();
+}
-- 
2.22.0

Re: [OFFLIST] [PATCH v1 0/2] pidfd: waiting on processes through pidfds

[Oleg Nesterov]

Hi Christian,

just fyi, can't read this patch till Monday


On 07/26, Christian Brauner wrote:
> Hey everyone,
> 
> /* v1 */
> This adds the ability to wait on processes using pidfds. This is one of
> the few missing pieces to make it possible to manage processes using
> only pidfds.
> 
> Please note the following major changes (More details can be found in
> the individual commit changelogs.):
> - Add the new type P_PIDFD to waitid() instead of a new dedicated
>   pidfd_wait() syscall.
>   This is the same approach we discussed a few months ago and still
>   prefer over adding a dedicated syscall.
> - Adapt the tests to the new type P_PIDFD for waitid().
> - Remove struct waitid_info patch.
>   This will be sent out as a separate patch.
> - Remove CLONE_WAIT_PID patch.
>   This will be sent out as a separate patch.
> 
> The core patch for waitid is pleasantly small. The largest change is
> caused by adding proper tests for waitid(P_PIDFD).
> 
> /* v0 */
> Link: https://lore.kernel.org/lkml/20190724144651.28272-1-christian@brauner.io
> 
> Thanks!
> Christian
> 
> Christian Brauner (2):
>   pidfd: add P_PIDFD to waitid()
>   pidfd: add pidfd_wait tests
> 
>  include/linux/pid.h                        |   4 +
>  include/uapi/linux/wait.h                  |   1 +
>  kernel/exit.c                              |  25 ++-
>  kernel/fork.c                              |   8 +
>  kernel/signal.c                            |   7 +-
>  tools/testing/selftests/pidfd/pidfd.h      |  25 +++
>  tools/testing/selftests/pidfd/pidfd_test.c |  14 --
>  tools/testing/selftests/pidfd/pidfd_wait.c | 245 +++++++++++++++++++++
>  8 files changed, 311 insertions(+), 18 deletions(-)
>  create mode 100644 tools/testing/selftests/pidfd/pidfd_wait.c
> 
> -- 
> 2.22.0
> 

Re: [PATCH v1 1/2] pidfd: add P_PIDFD to waitid()

[Linus Torvalds]

On Fri, Jul 26, 2019 at 2:41 AM Christian Brauner <christian@brauner.io> wrote:
>
> -       if (type < PIDTYPE_MAX)
> +       if (type < PIDTYPE_MAX && !pid)
>                 pid = find_get_pid(upid);

So now we have four cases in the switch statement, and two of them do
*not* want that "find_get_pid()" call.

Honestly, let's just move that whole thing into the switch statement
for the two cases that do want it. Particulartly since I think the
"upid == 0" case for P_PGID will prefer it that way anyway.

Let's not check 'type' in two different places in two completely
different ways.

Ok?

             Linus

Re: [PATCH v1 1/2] pidfd: add P_PIDFD to waitid()

[Christian Brauner]

On July 26, 2019 11:26:45 PM GMT+02:00, Linus Torvalds <torvalds@linux-foundation.org> wrote:
>On Fri, Jul 26, 2019 at 2:41 AM Christian Brauner
><christian@brauner.io> wrote:
>>
>> -       if (type < PIDTYPE_MAX)
>> +       if (type < PIDTYPE_MAX && !pid)
>>                 pid = find_get_pid(upid);
>
>So now we have four cases in the switch statement, and two of them do
>*not* want that "find_get_pid()" call.
>
>Honestly, let's just move that whole thing into the switch statement
>for the two cases that do want it. Particulartly since I think the
>"upid == 0" case for P_PGID will prefer it that way anyway.
>
>Let's not check 'type' in two different places in two completely
>different ways.
>
>Ok?
>
>             Linus

Ok, will resend with that changed.

Christian