Re: [PATCH v6 5/7] mm: support both pid and pidfd for process_madvise

This patch aims for supporting both options like waitid(2). So, the
syscall is currently,

        int process_madvise(int which, pid_t pid, void *addr,
                size_t length, int advise, unsigned long flag);

@which is actually idtype_t for userspace libray and currently,
it supports P_PID and P_PIDFD.

[1]  https://lore.kernel.org/linux-mm/9d849087-3359-c4ab-fbec-859e8186c509@virtuozzo.com/ (local)

Cc: Christian Brauner <christian@brauner.io>
Suggested-by: Kirill Tkhai <redacted>
Signed-off-by: Minchan Kim <minchan@kernel.org>
---
 include/linux/syscalls.h |  3 ++-
 mm/madvise.c             | 34 ++++++++++++++++++++++------------
 2 files changed, 24 insertions(+), 13 deletions(-)

diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index e4cd2c2f8bb4..f5ada20e2943 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h

@@ -876,7 +876,8 @@ asmlinkage long sys_munlockall(void);
 asmlinkage long sys_mincore(unsigned long start, size_t len,
                                unsigned char __user * vec);
 asmlinkage long sys_madvise(unsigned long start, size_t len, int behavior);
-asmlinkage long sys_process_madvise(int pidfd, unsigned long start,
+
+asmlinkage long sys_process_madvise(int which, pid_t pid, unsigned long start,
                        size_t len, int behavior, unsigned long flags);
 asmlinkage long sys_remap_file_pages(unsigned long start, unsigned long size,
                        unsigned long prot, unsigned long pgoff,

diff --git a/mm/madvise.c b/mm/madvise.c
index def1507c2030..f6d9b9e66243 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c

@@ -1182,11 +1182,10 @@ SYSCALL_DEFINE3(madvise, unsigned long, start, size_t, len_in, int, behavior)
        return do_madvise(current, current->mm, start, len_in, behavior);
 }

-SYSCALL_DEFINE5(process_madvise, int, pidfd, unsigned long, start,
+SYSCALL_DEFINE6(process_madvise, int, which, pid_t, upid, unsigned long, start,
                size_t, len_in, int, behavior, unsigned long, flags)
 {
        int ret;
-       struct fd f;
        struct pid *pid;
        struct task_struct *task;
        struct mm_struct *mm;

@@ -1197,20 +1196,31 @@ SYSCALL_DEFINE5(process_madvise, int, pidfd, unsigned long, start,
        if (!process_madvise_behavior_valid(behavior))
                return -EINVAL;

-       f = fdget(pidfd);
-       if (!f.file)
-               return -EBADF;
+       switch (which) {
+       case P_PID:
+               if (upid <= 0)
+                       return -EINVAL;
+
+               pid = find_get_pid(upid);
+               if (!pid)
+                       return -ESRCH;
+               break;
+       case P_PIDFD:
+               if (upid < 0)
+                       return -EINVAL;

-       pid = pidfd_pid(f.file);
-       if (IS_ERR(pid)) {
-               ret = PTR_ERR(pid);
-               goto fdput;
+               pid = pidfd_get_pid(upid);
+               if (IS_ERR(pid))
+                       return PTR_ERR(pid);
+               break;
+       default:
+               return -EINVAL;
        }

        task = get_pid_task(pid, PIDTYPE_PID);
        if (!task) {
                ret = -ESRCH;
-               goto fdput;
+               goto put_pid;
        }

        mm = mm_access(task, PTRACE_MODE_ATTACH_FSCREDS);

@@ -1223,7 +1233,7 @@ SYSCALL_DEFINE5(process_madvise, int, pidfd, unsigned long, start,
        mmput(mm);
 release_task:
        put_task_struct(task);
-fdput:
-       fdput(f);
+put_pid:
+       put_pid(pid);
        return ret;
 }
--

2.25.0.265.gbab2e86ba0-goog