mm: use pidfd_get_task()

Instead of duplicating the same code in two places use the newly added
pidfd_get_task() helper. This fixes an (unimportant for now) bug where
PIDTYPE_PID is used whereas PIDTYPE_TGID should have been used.

Link: https://lore.kernel.org/r/20211004125050.1153693-3-christian.brauner@ubuntu.com
Link: https://lore.kernel.org/r/20211011133245.1703103-3-brauner@kernel.org
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Matthew Bobrowski <repnop@google.com>
Cc: Alexander Duyck <alexander.h.duyck@linux.intel.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Minchan Kim <minchan@kernel.org>
Reviewed-by: Matthew Bobrowski <repnop@google.com>
Acked-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

Author: Christian Brauner

mm/madvise.c

@@ -1235,7 +1235,6 @@ SYSCALL_DEFINE5(process_madvise, int, pidfd, const struct iovec __user *, vec,
 	struct iovec iovstack[UIO_FASTIOV], iovec;
 	struct iovec *iov = iovstack;
 	struct iov_iter iter;
-	struct pid *pid;
 	struct task_struct *task;
 	struct mm_struct *mm;
 	size_t total_len;
@@ -1250,18 +1249,12 @@ SYSCALL_DEFINE5(process_madvise, int, pidfd, const struct iovec __user *, vec,
 	if (ret < 0)
 		goto out;
 
-	pid = pidfd_get_pid(pidfd, &f_flags);
-	if (IS_ERR(pid)) {
-		ret = PTR_ERR(pid);
+	task = pidfd_get_task(pidfd, &f_flags);
+	if (IS_ERR(task)) {
+		ret = PTR_ERR(task);
 		goto free_iov;
 	}
 
-	task = get_pid_task(pid, PIDTYPE_PID);
-	if (!task) {
-		ret = -ESRCH;
-		goto put_pid;
-	}
-
 	if (!process_madvise_behavior_valid(behavior)) {
 		ret = -EINVAL;
 		goto release_task;
@@ -1301,8 +1294,6 @@ SYSCALL_DEFINE5(process_madvise, int, pidfd, const struct iovec __user *, vec,
 	mmput(mm);
 release_task:
 	put_task_struct(task);
-put_pid:
-	put_pid(pid);
 free_iov:
 	kfree(iov);
 out:

mm/oom_kill.c

@@ -1151,21 +1151,14 @@ SYSCALL_DEFINE2(process_mrelease, int, pidfd, unsigned int, flags)
 	struct task_struct *p;
 	unsigned int f_flags;
 	bool reap = true;
-	struct pid *pid;
 	long ret = 0;
 
 	if (flags)
 		return -EINVAL;
 
-	pid = pidfd_get_pid(pidfd, &f_flags);
-	if (IS_ERR(pid))
-		return PTR_ERR(pid);
-
-	task = get_pid_task(pid, PIDTYPE_TGID);
-	if (!task) {
-		ret = -ESRCH;
-		goto put_pid;
-	}
+	task = pidfd_get_task(pidfd, &f_flags);
+	if (IS_ERR(task))
+		return PTR_ERR(task);
 
 	/*
 	 * Make sure to choose a thread which still has a reference to mm
@@ -1204,8 +1197,6 @@ SYSCALL_DEFINE2(process_mrelease, int, pidfd, unsigned int, flags)
 	mmdrop(mm);
 put_task:
 	put_task_struct(task);
-put_pid:
-	put_pid(pid);
 	return ret;
 #else
 	return -ENOSYS;