From 5a7f173601c5df604f5f2a4fdda61f8152507d4b Mon Sep 17 00:00:00 2001 From: Kan Liang Date: Wed, 6 Nov 2024 14:58:41 +0100 Subject: [PATCH] perf: Fix missing RCU reader protection in perf_event_clear_cpumask() Running rcutorture scenario TREE05, the below warning is triggered. [ 32.604594] WARNING: suspicious RCU usage [ 32.605928] 6.11.0-rc5-00040-g4ba4f1afb6a9 #55238 Not tainted [ 32.607812] ----------------------------- [ 32.609140] kernel/events/core.c:13946 RCU-list traversed in non-reader section!! [ 32.611595] other info that might help us debug this: [ 32.614247] rcu_scheduler_active = 2, debug_locks = 1 [ 32.616392] 3 locks held by cpuhp/4/35: [ 32.617687] #0: ffffffffb666a650 (cpu_hotplug_lock){++++}-{0:0}, at: cpuhp_thread_fun+0x4e/0x200 [ 32.620563] #1: ffffffffb666cd20 (cpuhp_state-down){+.+.}-{0:0}, at: cpuhp_thread_fun+0x4e/0x200 [ 32.623412] #2: ffffffffb677c288 (pmus_lock){+.+.}-{3:3}, at: perf_event_exit_cpu_context+0x32/0x2f0 In perf_event_clear_cpumask(), uses list_for_each_entry_rcu() without an obvious RCU read-side critical section. Either pmus_srcu or pmus_lock is good enough to protect the pmus list. In the current context, pmus_lock is already held. The list_for_each_entry_rcu() is not required. Fixes: 4ba4f1afb6a9 ("perf: Generic hotplug support for a PMU with a scope") Reported-by: Paul E. McKenney Closes: https://lore.kernel.org/lkml/2b66dff8-b827-494b-b151-1ad8d56f13e6@paulmck-laptop/ Tested-by: Paul E. McKenney Reported-by: kernel test robot Closes: https://lore.kernel.org/oe-lkp/202409131559.545634cc-oliver.sang@intel.com Signed-off-by: Kan Liang Suggested-by: Peter Zijlstra --- kernel/events/core.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/events/core.c b/kernel/events/core.c index cdd09769e6c5..df27d08a7232 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -13959,7 +13959,7 @@ static void perf_event_clear_cpumask(unsigned int cpu) } /* migrate */ - list_for_each_entry_rcu(pmu, &pmus, entry, lockdep_is_held(&pmus_srcu)) { + list_for_each_entry(pmu, &pmus, entry) { if (pmu->scope == PERF_PMU_SCOPE_NONE || WARN_ON_ONCE(pmu->scope >= PERF_PMU_MAX_SCOPE)) continue;