[PATCH V2] x86/resctrl: Fix rdt_find_domain() return value and checks

[Reinette Chatre]

rdt_find_domain() returns an ERR_PTR() that is generated from a provided
domain id when the value is negative.

Care needs to be taken when creating an ERR_PTR() from this value because
a subsequent check using IS_ERR() expects the error to be within the
MAX_ERRNO range. By using an invalid domain id as an ERR_PTR() does
work at this time since this is currently always -1. Using this
undocumented assumption is fragile since future users of
rdt_find_domain() may not be aware of thus assumption.

Two related issues are addressed:
- Ensure that rdt_find_domain() always returns a valid error value by
forcing the error to be -ENODEV when a negative domain id is provided.
- In a few instances the return value of rdt_find_domain() is just checked
for NULL - fix these to include a check of ERR_PTR.

Fixes: d89b7379015f ("x86/intel_rdt/cqm: Add mon_data")
Fixes: 521348b011d6 ("x86/intel_rdt: Introduce utility to obtain CDP peer")
Signed-off-by: Reinette Chatre <reinette.chatre@xxxxxxxxx>
---
V2:
- Force error value to be -ENODEV when negative domain id provided
- Rewrite commit message to describe why error value needs to be forced in
  addition to the original fix

 arch/x86/kernel/cpu/resctrl/core.c        | 2 +-
 arch/x86/kernel/cpu/resctrl/ctrlmondata.c | 2 +-
 arch/x86/kernel/cpu/resctrl/rdtgroup.c    | 2 +-
 3 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/cpu/resctrl/core.c b/arch/x86/kernel/cpu/resctrl/core.c
index 2ec252be4ed9..c3a9dc63edf2 100644
--- a/arch/x86/kernel/cpu/resctrl/core.c
+++ b/arch/x86/kernel/cpu/resctrl/core.c
@@ -454,7 +454,7 @@ struct rdt_domain *rdt_find_domain(struct rdt_resource *r, int id,
 	struct list_head *l;
 
 	if (id < 0)
-		return ERR_PTR(id);
+		return ERR_PTR(-ENODEV);
 
 	list_for_each(l, &r->domains) {
 		d = list_entry(l, struct rdt_domain, list);
diff --git a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
index ba11f54f5ab8..3b943ace786c 100644
--- a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
+++ b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
@@ -534,7 +534,7 @@ int rdtgroup_mondata_show(struct seq_file *m, void *arg)
 
 	r = &rdt_resources_all[resid];
 	d = rdt_find_domain(r, domid, NULL);
-	if (!d) {
+	if (IS_ERR_OR_NULL(d)) {
 		ret = -ENOENT;
 		goto out;
 	}
diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
index 017505017bdb..8388adf241b2 100644
--- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
+++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
@@ -1029,7 +1029,7 @@ static int rdt_cdp_peer_get(struct rdt_resource *r, struct rdt_domain *d,
 	 * peer RDT CDP resource. Hence the WARN.
 	 */
 	_d_cdp = rdt_find_domain(_r_cdp, d->id, NULL);
-	if (WARN_ON(!_d_cdp)) {
+	if (WARN_ON(IS_ERR_OR_NULL(_d_cdp))) {
 		_r_cdp = NULL;
 		ret = -EINVAL;
 	}
-- 
2.17.0