x86,fs/resctrl: Document safe RCU list traversal

Browse source

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

Show all changes Ignore whitespace when comparing lines Ignore changes in amount of whitespace Ignore changes in whitespace at EOL

Download patch file Download diff file Expand all files Collapse all files

4

arch/x86/kernel/cpu/resctrl/ctrlmondata.c

View file

2

arch/x86/kernel/cpu/resctrl/monitor.c

View file

4

arch/x86/kernel/cpu/resctrl/rdtgroup.c

View file

12

fs/resctrl/ctrlmondata.c

View file

23

fs/resctrl/monitor.c

View file

2

fs/resctrl/pseudo_lock.c

View file

24

fs/resctrl/rdtgroup.c

View file