Re: [PATCH 3/4] alloc_tag: extend allocinfo_filter to support tracing queries

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Critical] uapi: ALLOCINFO_IOC_GET_AT ioctl ABI breakage due to struct size increase
--

commit e19f22c2c2fb6885ec1ef8ea1659cf1ff9f8e3ae
Author: Abhishek Bapat <abhishekbapat@google.com>

alloc_tag: extend allocinfo_filter to support tracing queries

The commit extends the allocinfo filtering system to allow filtering by tracing
state. It adds a trace_on property to struct allocinfo_counter and a tracing
property to struct allocinfo_filter.

> diff --git a/include/uapi/linux/alloc_tag.h b/include/uapi/linux/alloc_tag.h
> index 069ab8341e87b..e65c32afceee2 100644
> --- a/include/uapi/linux/alloc_tag.h
> +++ b/include/uapi/linux/alloc_tag.h
[ ... ]
> @@ -75,6 +78,7 @@ struct allocinfo_filter {
>  	__u64 max_size;
>  	/* filter criteria only; see allocinfo_counter.accurate for actual accuracy */
>  	__u64 inaccurate;
> +	__u64 tracing;
>  };

[Severity: Critical]
Does adding __u64 tracing here cause an ioctl ABI regression for existing
userspace applications?

Since struct allocinfo_filter is embedded in struct allocinfo_get_at, adding
this field increases the size of struct allocinfo_get_at by 8 bytes.

The ioctl command ALLOCINFO_IOC_GET_AT is defined using _IOWR() which
incorporates the size of struct allocinfo_get_at into the command number:

include/uapi/linux/alloc_tag.h:
#define ALLOCINFO_IOC_GET_AT \
        _IOWR(ALLOCINFO_IOC_BASE, _ALLOCINFO_IOC_GET_AT, struct allocinfo_get_at)

When older userspace tools send the previous ioctl command number, will it
fail to match the new ALLOCINFO_IOC_GET_AT value in the switch statement
in allocinfo_ioctl():

mm/alloc_tag.c:allocinfo_ioctl() {
	switch (cmd) {
[ ... ]
	case ALLOCINFO_IOC_GET_AT:
		ret = allocinfo_ioctl_get_at(file->private_data, arg);
		break;
[ ... ]
	default:
		ret = -ENOIOCTLCMD;
		break;
	}
}

and cause requests to fall through to the default handler?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/cover.1790025465.git.abhishekbapat@google.com?part=3