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SubjectRe: [PATCH v6 5/7] mm: support both pid and pidfd for process_madvise
On Tue, Feb 18, 2020 at 5:44 PM Minchan Kim <minchan@kernel.org> wrote:
>
> There is a demand[1] to support pid as well pidfd for process_madvise
> to reduce unnecessary syscall to get pidfd if the user has control of
> the target process(ie, they could guarantee the process is not gone
> or pid is not reused. Or, it might be okay to give a hint to wrong
> process).

nit: When would "give a hint to wrong process" be ok? I would just
remove this part.

>
> 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/
>
> Cc: Christian Brauner <christian@brauner.io>
> Suggested-by: Kirill Tkhai <ktkhai@virtuozzo.com>
> 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
>

Reviewed-by: Suren Baghdasaryan <surenb@google.com>

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