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x86,fs/resctrl: Document safe RCU list traversal

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rdt_resource::ctrl_domains and rdt_resource::mon_domains are RCU lists with
entries added and removed by architecture from CPU hotplug callbacks that are
run with cpus_write_lock() held. These lists can be traversed safely from
resctrl fs by either holding cpus_read_lock() or relying on an RCU read-side
critical section.

resctrl fs traversals of rdt_resource::ctrl_domains and
rdt_resource::mon_domains are done using list_for_each_entry() with
cpus_read_lock() held. Similarly, x86 architecture callbacks use
list_for_each_entry() expecting that resctrl fs makes the call with
cpus_read_lock() held. Inconsistently, a lockdep_assert_cpus_held() precedes
the list_for_each_entry() call with varying distance to document this safe RCU
list traversal.

In preparation for an upcoming traversal of rdt_resource::ctrl_domains that
needs to be done from RCU read-side critical section there is a requirement
for developers to always know exactly in which context the list is being
traversed.

Replace the list_for_each_entry() traversals of RCU list with
list_for_each_entry_rcu() to document that an RCU list is being traversed
while making use of the built-in lockdep expression that additionally
documents that it is cpus_read_lock() that enables the list to be
traversed from non-RCU protection. Only revert to documenting the
safety of traversal using a comment when lockdep does not have needed
visibility in functions called via smp_call*().

The lockdep expression within list_for_each_entry_rcu() depends on
RCU_EXPERT that is not set in a typical debug kernel so keep the existing
lockdep_assert_cpus_held() that is active with CONFIG_LOCKDEP=y found in
typical debug kernel.

Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://patch.msgid.link/d9373f8da8ffde667740e186ffc96ab69628ac9a.1783963505.git.reinette.chatre@intel.com
This commit is contained in:
Reinette Chatre
2026-07-13 10:39:37 -07:00
committed by Borislav Petkov (AMD)
parent a13c140cc2
commit 11b57be8e4
7 changed files with 39 additions and 32 deletions
Download Patch File Download Diff File Expand all files Collapse all files

4
arch/x86/kernel/cpu/resctrl/ctrlmondata.c
View File

@@ -53,7 +53,7 @@ int resctrl_arch_update_domains(struct rdt_resource *r, u32 closid)
/* Walking r->domains, ensure it can't race with cpuhp */
lockdep_assert_cpus_held();
list_for_each_entry(d, &r->ctrl_domains, hdr.list) {
list_for_each_entry_rcu(d, &r->ctrl_domains, hdr.list, lockdep_is_cpus_held()) {
hw_dom = resctrl_to_arch_ctrl_dom(d);
msr_param.res = NULL;
for (t = 0; t < CDP_NUM_TYPES; t++) {
@@ -115,7 +115,7 @@ static void _resctrl_sdciae_enable(struct rdt_resource *r, bool enable)
lockdep_assert_cpus_held();
/* Update MSR_IA32_L3_QOS_EXT_CFG MSR on all the CPUs in all domains */
list_for_each_entry(d, &r->ctrl_domains, hdr.list)
list_for_each_entry_rcu(d, &r->ctrl_domains, hdr.list, lockdep_is_cpus_held())
on_each_cpu_mask(&d->hdr.cpu_mask, resctrl_sdciae_set_one_amd, &enable, 1);
}

2
arch/x86/kernel/cpu/resctrl/monitor.c
View File

@@ -510,7 +510,7 @@ static void _resctrl_abmc_enable(struct rdt_resource *r, bool enable)
lockdep_assert_cpus_held();
list_for_each_entry(d, &r->mon_domains, hdr.list) {
list_for_each_entry_rcu(d, &r->mon_domains, hdr.list, lockdep_is_cpus_held()) {
on_each_cpu_mask(&d->hdr.cpu_mask, resctrl_abmc_set_one_amd,
&enable, 1);
resctrl_arch_reset_rmid_all(r, d);

4
arch/x86/kernel/cpu/resctrl/rdtgroup.c
View File

@@ -151,7 +151,7 @@ static int set_cache_qos_cfg(int level, bool enable)
return -ENOMEM;
r_l = &rdt_resources_all[level].r_resctrl;
list_for_each_entry(d, &r_l->ctrl_domains, hdr.list) {
list_for_each_entry_rcu(d, &r_l->ctrl_domains, hdr.list, lockdep_is_cpus_held()) {
if (r_l->cache.arch_has_per_cpu_cfg)
/* Pick all the CPUs in the domain instance */
for_each_cpu(cpu, &d->hdr.cpu_mask)
@@ -249,7 +249,7 @@ void resctrl_arch_reset_all_ctrls(struct rdt_resource *r)
* CBMs in all ctrl_domains to the maximum mask value. Pick one CPU
* from each domain to update the MSRs below.
*/
list_for_each_entry(d, &r->ctrl_domains, hdr.list) {
list_for_each_entry_rcu(d, &r->ctrl_domains, hdr.list, lockdep_is_cpus_held()) {
hw_dom = resctrl_to_arch_ctrl_dom(d);
for (i = 0; i < hw_res->num_closid; i++)

12
fs/resctrl/ctrlmondata.c
View File

@@ -261,7 +261,7 @@ static int parse_line(char *line, struct resctrl_schema *s,
return -EINVAL;
}
dom = strim(dom);
list_for_each_entry(d, &r->ctrl_domains, hdr.list) {
list_for_each_entry_rcu(d, &r->ctrl_domains, hdr.list, lockdep_is_cpus_held()) {
if (d->hdr.id == dom_id) {
data.buf = dom;
data.closid = rdtgrp->closid;
@@ -397,7 +397,7 @@ static void show_doms(struct seq_file *s, struct resctrl_schema *schema,
if (resource_name)
seq_printf(s, "%*s:", max_name_width, resource_name);
list_for_each_entry(dom, &r->ctrl_domains, hdr.list) {
list_for_each_entry_rcu(dom, &r->ctrl_domains, hdr.list, lockdep_is_cpus_held()) {
if (sep)
seq_puts(s, ";");
@@ -535,6 +535,8 @@ struct rdt_domain_hdr *resctrl_find_domain(struct list_head *h, int id,
struct rdt_domain_hdr *d;
struct list_head *l;
lockdep_assert_cpus_held();
list_for_each(l, h) {
d = list_entry(l, struct rdt_domain_hdr, list);
/* When id is found, return its domain. */
@@ -717,7 +719,7 @@ int rdtgroup_mondata_show(struct seq_file *m, void *arg)
* struct mon_data. Search all domains in the resource for
* one that matches this cache id.
*/
list_for_each_entry(d, &r->mon_domains, hdr.list) {
list_for_each_entry_rcu(d, &r->mon_domains, hdr.list, lockdep_is_cpus_held()) {
if (d->ci_id == domid) {
cpu = cpumask_any(&d->hdr.cpu_mask);
ci = get_cpu_cacheinfo_level(cpu, RESCTRL_L3_CACHE);
@@ -817,7 +819,7 @@ static int resctrl_io_alloc_init_cbm(struct resctrl_schema *s, u32 closid)
/* Keep CDP_CODE and CDP_DATA of io_alloc CLOSID's CBM in sync. */
if (resctrl_arch_get_cdp_enabled(r->rid)) {
peer_type = resctrl_peer_type(s->conf_type);
list_for_each_entry(d, &s->res->ctrl_domains, hdr.list)
list_for_each_entry_rcu(d, &s->res->ctrl_domains, hdr.list, lockdep_is_cpus_held())
memcpy(&d->staged_config[peer_type],
&d->staged_config[s->conf_type],
sizeof(d->staged_config[0]));
@@ -980,7 +982,7 @@ static int resctrl_io_alloc_parse_line(char *line, struct rdt_resource *r,
}
dom = strim(dom);
list_for_each_entry(d, &r->ctrl_domains, hdr.list) {
list_for_each_entry_rcu(d, &r->ctrl_domains, hdr.list, lockdep_is_cpus_held()) {
if (update_all || d->hdr.id == dom_id) {
data.buf = dom;
data.mode = RDT_MODE_SHAREABLE;

23
fs/resctrl/monitor.c
View File

@@ -309,7 +309,7 @@ static void add_rmid_to_limbo(struct rmid_entry *entry)
idx = resctrl_arch_rmid_idx_encode(entry->closid, entry->rmid);
entry->busy = 0;
list_for_each_entry(d, &r->mon_domains, hdr.list) {
list_for_each_entry_rcu(d, &r->mon_domains, hdr.list, lockdep_is_cpus_held()) {
/*
* For the first limbo RMID in the domain,
* setup up the limbo worker.
@@ -507,6 +507,11 @@ static int __l3_mon_event_count_sum(struct rdtgroup *rdtgrp, struct rmid_read *r
* all domains fail for any reason.
*/
ret = -EINVAL;
/*
* RCU list being traversed with CPU hotplug lock held. lockdep
* unable to help prove this here since this work is scheduled via
* smp_call*(). Not called from MBM overflow handler.
*/
list_for_each_entry(d, &rr->r->mon_domains, hdr.list) {
if (d->ci_id != rr->ci->id)
continue;
@@ -1231,7 +1236,7 @@ static int rdtgroup_assign_cntr_event(struct rdt_l3_mon_domain *d, struct rdtgro
int ret = 0;
if (!d) {
list_for_each_entry(d, &r->mon_domains, hdr.list) {
list_for_each_entry_rcu(d, &r->mon_domains, hdr.list, lockdep_is_cpus_held()) {
int err;
err = rdtgroup_alloc_assign_cntr(r, d, rdtgrp, mevt);
@@ -1303,7 +1308,7 @@ static void rdtgroup_unassign_cntr_event(struct rdt_l3_mon_domain *d, struct rdt
struct rdt_resource *r = resctrl_arch_get_resource(mevt->rid);
if (!d) {
list_for_each_entry(d, &r->mon_domains, hdr.list)
list_for_each_entry_rcu(d, &r->mon_domains, hdr.list, lockdep_is_cpus_held())
rdtgroup_free_unassign_cntr(r, d, rdtgrp, mevt);
} else {
rdtgroup_free_unassign_cntr(r, d, rdtgrp, mevt);
@@ -1375,7 +1380,7 @@ static void rdtgroup_update_cntr_event(struct rdt_resource *r, struct rdtgroup *
struct rdt_l3_mon_domain *d;
int cntr_id;
list_for_each_entry(d, &r->mon_domains, hdr.list) {
list_for_each_entry_rcu(d, &r->mon_domains, hdr.list, lockdep_is_cpus_held()) {
cntr_id = mbm_cntr_get(r, d, rdtgrp, evtid);
if (cntr_id >= 0)
rdtgroup_assign_cntr(r, d, evtid, rdtgrp->mon.rmid,
@@ -1545,7 +1550,7 @@ ssize_t resctrl_mbm_assign_mode_write(struct kernfs_open_file *of, char *buf,
/*
* Reset all the non-achitectural RMID state and assignable counters.
*/
list_for_each_entry(d, &r->mon_domains, hdr.list) {
list_for_each_entry_rcu(d, &r->mon_domains, hdr.list, lockdep_is_cpus_held()) {
mbm_cntr_free_all(r, d);
resctrl_reset_rmid_all(r, d);
}
@@ -1568,7 +1573,7 @@ int resctrl_num_mbm_cntrs_show(struct kernfs_open_file *of,
cpus_read_lock();
mutex_lock(&rdtgroup_mutex);
list_for_each_entry(dom, &r->mon_domains, hdr.list) {
list_for_each_entry_rcu(dom, &r->mon_domains, hdr.list, lockdep_is_cpus_held()) {
if (sep)
seq_putc(s, ';');
@@ -1602,7 +1607,7 @@ int resctrl_available_mbm_cntrs_show(struct kernfs_open_file *of,
goto out_unlock;
}
list_for_each_entry(dom, &r->mon_domains, hdr.list) {
list_for_each_entry_rcu(dom, &r->mon_domains, hdr.list, lockdep_is_cpus_held()) {
if (sep)
seq_putc(s, ';');
@@ -1652,7 +1657,7 @@ int mbm_L3_assignments_show(struct kernfs_open_file *of, struct seq_file *s, voi
sep = false;
seq_printf(s, "%s:", mevt->name);
list_for_each_entry(d, &r->mon_domains, hdr.list) {
list_for_each_entry_rcu(d, &r->mon_domains, hdr.list, lockdep_is_cpus_held()) {
if (sep)
seq_putc(s, ';');
@@ -1750,7 +1755,7 @@ static int resctrl_parse_mbm_assignment(struct rdt_resource *r, struct rdtgroup
}
/* Verify if the dom_id is valid */
list_for_each_entry(d, &r->mon_domains, hdr.list) {
list_for_each_entry_rcu(d, &r->mon_domains, hdr.list, lockdep_is_cpus_held()) {
if (d->hdr.id == dom_id) {
ret = rdtgroup_modify_assign_state(dom_str, d, rdtgrp, mevt);
if (ret) {

2
fs/resctrl/pseudo_lock.c
View File

@@ -656,7 +656,7 @@ bool rdtgroup_pseudo_locked_in_hierarchy(struct rdt_ctrl_domain *d)
* associated with them.
*/
for_each_alloc_capable_rdt_resource(r) {
list_for_each_entry(d_i, &r->ctrl_domains, hdr.list) {
list_for_each_entry_rcu(d_i, &r->ctrl_domains, hdr.list, lockdep_is_cpus_held()) {
if (d_i->plr)
cpumask_or(cpu_with_psl, cpu_with_psl,
&d_i->hdr.cpu_mask);

24
fs/resctrl/rdtgroup.c
View File

@@ -119,7 +119,7 @@ void rdt_staged_configs_clear(void)
lockdep_assert_held(&rdtgroup_mutex);
for_each_alloc_capable_rdt_resource(r) {
list_for_each_entry(dom, &r->ctrl_domains, hdr.list)
list_for_each_entry_rcu(dom, &r->ctrl_domains, hdr.list, lockdep_is_cpus_held())
memset(dom->staged_config, 0, sizeof(dom->staged_config));
}
}
@@ -1071,7 +1071,7 @@ static int rdt_bit_usage_show(struct kernfs_open_file *of,
cpus_read_lock();
mutex_lock(&rdtgroup_mutex);
list_for_each_entry(dom, &r->ctrl_domains, hdr.list) {
list_for_each_entry_rcu(dom, &r->ctrl_domains, hdr.list, lockdep_is_cpus_held()) {
if (sep)
seq_putc(seq, ';');
hw_shareable = r->cache.shareable_bits;
@@ -1423,7 +1423,7 @@ static bool rdtgroup_mode_test_exclusive(struct rdtgroup *rdtgrp)
if (r->rid == RDT_RESOURCE_MBA || r->rid == RDT_RESOURCE_SMBA)
continue;
has_cache = true;
list_for_each_entry(d, &r->ctrl_domains, hdr.list) {
list_for_each_entry_rcu(d, &r->ctrl_domains, hdr.list, lockdep_is_cpus_held()) {
ctrl = resctrl_arch_get_config(r, d, closid,
s->conf_type);
if (rdtgroup_cbm_overlaps(s, d, ctrl, closid, false)) {
@@ -1612,7 +1612,7 @@ static int rdtgroup_size_show(struct kernfs_open_file *of,
type = schema->conf_type;
sep = false;
seq_printf(s, "%*s:", max_name_width, schema->name);
list_for_each_entry(d, &r->ctrl_domains, hdr.list) {
list_for_each_entry_rcu(d, &r->ctrl_domains, hdr.list, lockdep_is_cpus_held()) {
if (sep)
seq_putc(s, ';');
if (rdtgrp->mode == RDT_MODE_PSEUDO_LOCKSETUP) {
@@ -1657,7 +1657,7 @@ static int mbm_config_show(struct seq_file *s, struct rdt_resource *r, u32 evtid
cpus_read_lock();
mutex_lock(&rdtgroup_mutex);
list_for_each_entry(dom, &r->mon_domains, hdr.list) {
list_for_each_entry_rcu(dom, &r->mon_domains, hdr.list, lockdep_is_cpus_held()) {
if (sep)
seq_puts(s, ";");
@@ -1771,7 +1771,7 @@ static int mon_config_write(struct rdt_resource *r, char *tok, u32 evtid)
return -EINVAL;
}
list_for_each_entry(d, &r->mon_domains, hdr.list) {
list_for_each_entry_rcu(d, &r->mon_domains, hdr.list, lockdep_is_cpus_held()) {
if (d->hdr.id == dom_id) {
mbm_config_write_domain(r, d, evtid, val);
goto next;
@@ -2562,7 +2562,7 @@ static int set_mba_sc(bool mba_sc)
rdtgroup_default.mba_mbps_event = mba_mbps_default_event;
list_for_each_entry(d, &r->ctrl_domains, hdr.list) {
list_for_each_entry_rcu(d, &r->ctrl_domains, hdr.list, lockdep_is_cpus_held()) {
for (i = 0; i < num_closid; i++)
d->mbps_val[i] = MBA_MAX_MBPS;
}
@@ -2893,7 +2893,7 @@ static int rdt_get_tree(struct fs_context *fc)
if (resctrl_is_mbm_enabled()) {
r = resctrl_arch_get_resource(RDT_RESOURCE_L3);
list_for_each_entry(dom, &r->mon_domains, hdr.list)
list_for_each_entry_rcu(dom, &r->mon_domains, hdr.list, lockdep_is_cpus_held())
mbm_setup_overflow_handler(dom, MBM_OVERFLOW_INTERVAL,
RESCTRL_PICK_ANY_CPU);
}
@@ -3453,7 +3453,7 @@ static int mkdir_mondata_subdir_alldom(struct kernfs_node *parent_kn,
/* Walking r->domains, ensure it can't race with cpuhp */
lockdep_assert_cpus_held();
list_for_each_entry(hdr, &r->mon_domains, list) {
list_for_each_entry_rcu(hdr, &r->mon_domains, list, lockdep_is_cpus_held()) {
ret = mkdir_mondata_subdir(parent_kn, hdr, r, prgrp);
if (ret)
return ret;
@@ -3638,7 +3638,7 @@ int rdtgroup_init_cat(struct resctrl_schema *s, u32 closid)
struct rdt_ctrl_domain *d;
int ret;
list_for_each_entry(d, &s->res->ctrl_domains, hdr.list) {
list_for_each_entry_rcu(d, &s->res->ctrl_domains, hdr.list, lockdep_is_cpus_held()) {
ret = __init_one_rdt_domain(d, s, closid);
if (ret < 0)
return ret;
@@ -3653,7 +3653,7 @@ static void rdtgroup_init_mba(struct rdt_resource *r, u32 closid)
struct resctrl_staged_config *cfg;
struct rdt_ctrl_domain *d;
list_for_each_entry(d, &r->ctrl_domains, hdr.list) {
list_for_each_entry_rcu(d, &r->ctrl_domains, hdr.list, lockdep_is_cpus_held()) {
if (is_mba_sc(r)) {
d->mbps_val[closid] = MBA_MAX_MBPS;
continue;
@@ -4525,7 +4525,7 @@ static struct rdt_l3_mon_domain *get_mon_domain_from_cpu(int cpu,
lockdep_assert_cpus_held();
list_for_each_entry(d, &r->mon_domains, hdr.list) {
list_for_each_entry_rcu(d, &r->mon_domains, hdr.list, lockdep_is_cpus_held()) {
/* Find the domain that contains this CPU */
if (cpumask_test_cpu(cpu, &d->hdr.cpu_mask))
return d;