Re: [PATCH v2] pidfs: ensure that PIDFS_INFO_EXIT is available

[Oleg Nesterov <oleg@redhat.com>]

I'll try to actually read this patch (and pidfs: improve multi-threaded
exec and premature thread-group leader exit polling) tomorrow, but I am
a bit confused after the quick glance...


On 03/18, Christian Brauner wrote:
>
> +static inline bool pidfs_pid_valid(struct pid *pid, const struct path *path,
> +				   unsigned int flags)
> +{
> +	enum pid_type type;
> +
> +	if (flags & CLONE_PIDFD)
> +		return true;

OK, this is clear.

> +	if (flags & PIDFD_THREAD)
> +		type = PIDTYPE_PID;
> +	else
> +		type = PIDTYPE_TGID;
> +
> +	/*
> +	 * Since pidfs_exit() is called before struct pid's task linkage
> +	 * is removed the case where the task got reaped but a dentry
> +	 * was already attached to struct pid and exit information was
> +	 * recorded and published can be handled correctly.
> +	 */
> +	if (unlikely(!pid_has_task(pid, type))) {
> +		struct inode *inode = d_inode(path->dentry);
> +		return !!READ_ONCE(pidfs_i(inode)->exit_info);
> +	}

Why pidfs_pid_valid() can't simply return false if !pid_has_task(pid,type) ?

pidfd_open() paths check pid_has_task() too and fail if it returns NULL.
If this task is already reaped when pidfs_pid_valid() is called, we can
pretend it was reaped before sys_pidfd_open() was called?

Oleg.