From: Willem de Bruijn <[email protected]>
Resctrl takes an extra kernfs ref on directory entries, to access
the entry on cleanup in rdtgroup_kn_unlock after removing the entire
subtree with kfree_remove.
But the path takes an extra ref both on mkdir and on rmdir.
The kernfs_get on mkdir causes a memleak in the unlikely exit with
error in the same function, as no extra kernfs_put exists and no extra
rdtgroup_kn_unlock occurs.
More importantly, essentially the same happens in the normal path, as
this simple program demonstrates:
for i in {1..200000}; do
mkdir /sys/fs/resctrl/task1
rmdir /sys/fs/resctrl/task1
done
slabtop
When taking an extra ref for the duration of kernfs_remove, it is
easiest to reason about when holding this extra ref as short as
possible. For that, the refcnt on error reason and free on umount
(rmdir_all_sub), remove the first kernfs_get on mkdir, leaving the
other on rmdir.
As the caller of rdtgroup_rmdir, kernfs_iop_rmdir, itself takes a
reference on the kernfs object, the extra reference is possibly not
needed at all.
Fixes: 60cf5e101fd4 ("x86/intel_rdt: Add mkdir to resctrl file system")
Signed-off-by: Willem de Bruijn <[email protected]>
---
arch/x86/kernel/cpu/resctrl/rdtgroup.c | 8 --------
1 file changed, 8 deletions(-)
diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
index 4d02ec8f371e..115a86bf6bd8 100644
--- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
+++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
@@ -2839,14 +2839,6 @@ static int mkdir_rdt_prepare(struct kernfs_node
*parent_kn,
}
rdtgrp->kn = kn;
- /*
- * kernfs_remove() will drop the reference count on "kn" which
- * will free it. But we still need it to stick around for the
- * rdtgroup_kn_unlock(kn} call below. Take one extra reference
- * here, which will be dropped inside rdtgroup_kn_unlock().
- */
- kernfs_get(kn);
-
ret = rdtgroup_kn_set_ugid(kn);
if (ret) {
rdt_last_cmd_puts("kernfs perm error\n");
--
2.29.0.rc1.297.gfa9743e501-goog
