On Thu, Feb 22, 2024 at 12:40:54PM -0800, Dan Williams wrote:
It turns out that arch/x86/events/intel/core.c makes use of "empty" attributes.
static struct attribute *empty_attrs;
__init int intel_pmu_init(void) { struct attribute **extra_skl_attr = &empty_attrs; struct attribute **extra_attr = &empty_attrs; struct attribute **td_attr = &empty_attrs; struct attribute **mem_attr = &empty_attrs; struct attribute **tsx_attr = &empty_attrs; ...
That breaks the assumption __first_visible() that expects that if grp->attrs is set then grp->attrs[0] must also be set and results in backtraces like:
BUG: kernel NULL pointer dereference, address: 00rnel mode #PF: error_code(0x0000) - not-present ] PREEMPT SMP NOPTI CPU: 1 PID: 1 Comm: swapper/IP: 0010:exra_is_visible+0x14/0x20 ? exc_page_fault+0x68/0x190 internal_create_groups+0x42/0xa0 pmu_dev_alloc+0xc0/0xe0 perf_event_sysfs_init+0x580000000000 ]--- RIP: 0010:exra_is_visible+0x14/0Check for non-empty attributes array before calling is_visible().
[...]
--- a/fs/sysfs/group.c +++ b/fs/sysfs/group.c @@ -33,10 +33,10 @@ static void remove_files(struct kernfs_node *parent,
static umode_t __first_visible(const struct attribute_group *grp, struct kobject *kobj) {
- if (grp->attrs && grp->is_visible)
- if (grp->attrs && grp->attrs[0] && grp->is_visible) return grp->is_visible(kobj, grp->attrs[0], 0);
- if (grp->bin_attrs && grp->is_bin_visible)
if (grp->bin_attrs && grp->bin_attrs[0] && grp->is_bin_visible) return grp->is_bin_visible(kobj, grp->bin_attrs[0], 0);
return 0;
I'm wondering why 0 is returned by default and not SYSFS_GROUP_INVISIBLE.
An empty attribute list (containing just the NULL sentinel) will now result in the attribute group being visible as an empty directory.
I thought the whole point was to hide such empty directories.
Was it a conscious decision to return 0? Did you expect breakage if SYSFS_GROUP_INVISIBLE is returned?
Thanks,
Lukas