From: Arnd Bergmann <arnd@xxxxxxxx>
When cgroups are enabled, but every single subsystem is turned off,
CGROUP_SUBSYS_COUNT is zero, and the cgrp->subsys[] array has no
members.
gcc-11 points out that this leads to an invalid access in any function
that might access this array:
kernel/cgroup/cgroup.c: In function 'cgroup_addrm_files':
kernel/cgroup/cgroup.c:460:58: warning: array subscript '<unknown>' is outside the bounds of an interior zero-length array 'struct cgroup_subsys_state *[0]' [-Wzero-length-bounds]
kernel/cgroup/cgroup.c:460:24: note: in expansion of macro 'rcu_dereference_check'
460 | return rcu_dereference_check(cgrp->subsys[ss->id],
| ^~~~~~~~~~~~~~~~~~~~~
In file included from include/linux/cgroup.h:28,
from kernel/cgroup/cgroup-internal.h:5,
from kernel/cgroup/cgroup.c:31:
include/linux/cgroup-defs.h:422:43: note: while referencing 'subsys'
422 | struct cgroup_subsys_state __rcu *subsys[CGROUP_SUBSYS_COUNT];
I'm not sure what is expected to happen for such a configuration,
presumably these functions are never calls in that case. Adding a
sanity check in each function we get the warning for manages to shut
up the warnings and do nothing instead.
Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
---
I'm grouping this together with the -Wstringop-overread warnings,
since the underlying logic in gcc seems to be the same.
---
kernel/cgroup/cgroup.c | 15 ++++++++++++---
1 file changed, 12 insertions(+), 3 deletions(-)
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 9153b20e5cc6..3477f1dc7872 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -456,7 +456,7 @@ static u16 cgroup_ss_mask(struct cgroup *cgrp)
static struct cgroup_subsys_state *cgroup_css(struct cgroup *cgrp,
struct cgroup_subsys *ss)
{
- if (ss)
+ if (ss && (CGROUP_SUBSYS_COUNT > 0))
return rcu_dereference_check(cgrp->subsys[ss->id],
lockdep_is_held(&cgroup_mutex));
else
@@ -534,6 +534,9 @@ struct cgroup_subsys_state *cgroup_e_css(struct cgroup *cgrp,
{
struct cgroup_subsys_state *css;
+ if (CGROUP_SUBSYS_COUNT == 0)
+ return NULL;
+
do {
css = cgroup_css(cgrp, ss);
@@ -561,6 +564,9 @@ struct cgroup_subsys_state *cgroup_get_e_css(struct cgroup *cgrp,
{
struct cgroup_subsys_state *css;
+ if (CGROUP_SUBSYS_COUNT == 0)
+ return NULL;
+
rcu_read_lock();
do {
@@ -630,7 +636,7 @@ struct cgroup_subsys_state *of_css(struct kernfs_open_file *of)
* the matching css from the cgroup's subsys table is guaranteed to
* be and stay valid until the enclosing operation is complete.
*/
- if (cft->ss)
+ if (cft->ss && CGROUP_SUBSYS_COUNT > 0)
return rcu_dereference_raw(cgrp->subsys[cft->ss->id]);
else
return &cgrp->self;
@@ -2343,6 +2349,9 @@ struct task_struct *cgroup_taskset_next(struct cgroup_taskset *tset,
struct css_set *cset = tset->cur_cset;
struct task_struct *task = tset->cur_task;
+ if (CGROUP_SUBSYS_COUNT == 0)
+ return NULL;
+
while (&cset->mg_node != tset->csets) {
if (!task)
task = list_first_entry(&cset->mg_tasks,
@@ -4523,7 +4532,7 @@ void css_task_iter_start(struct cgroup_subsys_state *css, unsigned int flags,
it->ss = css->ss;
it->flags = flags;
- if (it->ss)
+ if (it->ss && CGROUP_SUBSYS_COUNT > 0)
it->cset_pos = &css->cgroup->e_csets[css->ss->id];
else
it->cset_pos = &css->cgroup->cset_links;
--
2.29.2
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