Subsystems that want to register CPU hotplug callbacks, as well as perform
initialization for the CPUs that are already online, often do it as shown
below:
get_online_cpus();
for_each_online_cpu(cpu)
init_cpu(cpu);
register_cpu_notifier(&foobar_cpu_notifier);
put_online_cpus();
This is wrong, since it is prone to ABBA deadlocks involving the
cpu_add_remove_lock and the cpu_hotplug.lock (when running concurrently
with CPU hotplug operations).
Instead, the correct and race-free way of performing the callback
registration is:
cpu_notifier_register_begin();
for_each_online_cpu(cpu)
init_cpu(cpu);
/* Note the use of the double underscored version of the API */
__register_cpu_notifier(&foobar_cpu_notifier);
cpu_notifier_register_done();
Fix the profile code by using this latter form of callback registration.
Cc: Al Viro <v...@zeniv.linux.org.uk>
Cc: Mauro Carvalho Chehab <mche...@redhat.com>
Cc: Ingo Molnar <mi...@kernel.org>
Signed-off-by: Srivatsa S. Bhat <srivatsa.b...@linux.vnet.ibm.com>
---
kernel/profile.c | 20 +++++++++++++++-----
1 file changed, 15 insertions(+), 5 deletions(-)
diff --git a/kernel/profile.c b/kernel/profile.c
index 6631e1e..4c0cb95 100644
--- a/kernel/profile.c
+++ b/kernel/profile.c
@@ -591,18 +591,28 @@ out_cleanup:
int __ref create_proc_profile(void) /* false positive from hotcpu_notifier */
{
struct proc_dir_entry *entry;
+ int err = 0;
if (!prof_on)
return 0;
- if (create_hash_tables())
- return -ENOMEM;
+
+ cpu_notifier_register_begin();
+
+ if (create_hash_tables()) {
+ err = -ENOMEM;
+ goto out;
+ }
+
entry = proc_create("profile", S_IWUSR | S_IRUGO,
NULL, &proc_profile_operations);
if (!entry)
- return 0;
+ goto out;
proc_set_size(entry, (1 + prof_len) * sizeof(atomic_t));
- hotcpu_notifier(profile_cpu_callback, 0);
- return 0;
+ __hotcpu_notifier(profile_cpu_callback, 0);
+
+out:
+ cpu_notifier_register_done();
+ return err;
}
module_init(create_proc_profile);
#endif /* CONFIG_PROC_FS */
--
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