| From | "Srivatsa S. Bhat" <> | Subject | [PATCH 47/51] profile: Fix CPU hotplug callback registration | Date | Thu, 06 Feb 2014 03:43:10 +0530 |
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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_maps_update_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_maps_update_done();
Fix the profile code by using this latter form of callback registration.
Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Mauro Carvalho Chehab <mchehab@redhat.com> Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@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..df27769 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_maps_update_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_maps_update_done(); + return err; } module_init(create_proc_profile); #endif /* CONFIG_PROC_FS */
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