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profile: Fix CPU hotplug callback registration

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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_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 <viro@zeniv.linux.org.uk>
Cc: Mauro Carvalho Chehab <mchehab@redhat.com>
Cc: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Git-commit: c270a817196a9374a2dc730624d1501dced40b4d
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
Signed-off-by: Osvaldo Banuelos <osvaldob@codeaurora.org>
This commit is contained in:
Srivatsa S. Bhat 2014-02-14 12:13:37 +05:30 committed by Osvaldo Banuelos
parent 276902b629
commit 284c1cd4b8
1 changed files with 15 additions and 5 deletions
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20
kernel/profile.c
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@ -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 */