sched/cache: Annotate lockless accesses to mm->sc_stat.cpu

Browse source

mm->sc_stat.cpu is written by task_cache_work() and could be read
locklessly by several functions on other CPUs.  Use READ_ONCE and
WRITE_ONCE on mm->sc_stat.cpu access and write to prevent inconsistent
values from compiler optimizations when there are multiple accesses.

For example in get_pref_llc(), if the writer updated the field between
two compiler-generated loads, the validation (e.g., cpu != -1) and
subsequent use (e.g., llc_id(cpu)) could operate on different values,
allowing a negative CPU ID to be used as an index.

Leave plain write in mm_init_sched(), where the mm is not
yet visible to other CPUs.

This bug was reported by sashiko.

Fixes: 47d8696b95 ("sched/cache: Assign preferred LLC ID to processes")
Signed-off-by: Chen Yu <yu.c.chen@intel.com>
Co-developed-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/63ea494f12efcf265d7134400a06cd75d7f2c310.1778703694.git.tim.c.chen@linux.intel.com

...

This commit is contained in:

Chen Yu 2026-05-13 13:39:20 -07:00 • committed by Peter Zijlstra

parent 9f23469401

commit 91d07324c9

1 changed files with 15 additions and 14 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

29

kernel/sched/fair.c

View file