Am Di., 28. Okt. 2025 um 09:46 Uhr schrieb Christian Brauner
<brauner@kernel.org>:
>
> There will likely be more info that we need to store in struct
> pidfs_attr. We need to make sure that some of the information such as
> exit info or coredump info that consists of multiple bits is either
> available completely or not at all, but never partially. Currently we
> use a pointer that we assign to. That doesn't scale. We can't waste a
> pointer for each mulit-part information struct we want to expose. Use a
> bitmask instead.
>
> Signed-off-by: Christian Brauner <brauner@kernel.org>
Reviewed-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>
> ---
> fs/pidfs.c | 12 +++++++++---
> 1 file changed, 9 insertions(+), 3 deletions(-)
>
> diff --git a/fs/pidfs.c b/fs/pidfs.c
> index 204ebd32791a..0fad0c969b7a 100644
> --- a/fs/pidfs.c
> +++ b/fs/pidfs.c
> @@ -49,7 +49,12 @@ struct pidfs_exit_info {
> __u32 coredump_mask;
> };
>
> +enum pidfs_attr_mask_bits {
> + PIDFS_ATTR_BIT_EXIT = 0,
> +};
> +
> struct pidfs_attr {
> + unsigned long attr_mask;
> struct simple_xattrs *xattrs;
> struct pidfs_exit_info __pei;
> struct pidfs_exit_info *exit_info;
> @@ -333,8 +338,8 @@ static long pidfd_info(struct file *file, unsigned int cmd, unsigned long arg)
>
> attr = READ_ONCE(pid->attr);
> if (mask & PIDFD_INFO_EXIT) {
> - exit_info = READ_ONCE(attr->exit_info);
> - if (exit_info) {
> + if (test_bit(PIDFS_ATTR_BIT_EXIT, &attr->attr_mask)) {
> + smp_rmb();
> kinfo.mask |= PIDFD_INFO_EXIT;
> #ifdef CONFIG_CGROUPS
> kinfo.cgroupid = exit_info->cgroupid;
> @@ -663,7 +668,8 @@ void pidfs_exit(struct task_struct *tsk)
> exit_info->exit_code = tsk->exit_code;
>
> /* Ensure that PIDFD_GET_INFO sees either all or nothing. */
> - smp_store_release(&attr->exit_info, &attr->__pei);
> + smp_wmb();
> + set_bit(PIDFS_ATTR_BIT_EXIT, &attr->attr_mask);
> }
>
> #ifdef CONFIG_COREDUMP
>
> --
> 2.47.3
>