tree fd43f8bde33e8135e00fee274e99ff8a48adf939
parent 4291154ca3d267b53196a67435fc9e6dfcb8b0b3
author Kan Liang <kan.liang@linux.intel.com> 1726244620 -0700
committer Paul E. McKenney <paulmck@kernel.org> 1728491485 -0700

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 <paulmck@kernel.org>
Closes: https://lore.kernel.org/lkml/2b66dff8-b827-494b-b151-1ad8d56f13e6@paulmck-laptop/
Tested-by: Paul E. McKenney <paulmck@kernel.org>
Reported-by: kernel test robot <oliver.sang@intel.com>
Closes: https://lore.kernel.org/oe-lkp/202409131559.545634cc-oliver.sang@intel.com
Signed-off-by: Kan Liang <kan.liang@linux.intel.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>