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md/raid5: 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).

Interestingly, the raid5 code can actually prevent double initialization and
hence can use the following simplified form of callback registration:

	register_cpu_notifier(&foobar_cpu_notifier);

	get_online_cpus();

	for_each_online_cpu(cpu)
		init_cpu(cpu);

	put_online_cpus();

A hotplug operation that occurs between registering the notifier and calling
get_online_cpus(), won't disrupt anything, because the code takes care to
perform the memory allocations only once.

So reorganize the code in raid5 this way to fix the deadlock with callback
registration.

Cc: linux-raid@vger.kernel.org
Cc: stable@vger.kernel.org (v2.6.32+)
Fixes: 36d1c6476b
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
[Srivatsa: Fixed the unregister_cpu_notifier() deadlock, added the
free_scratch_buffer() helper to condense code further and wrote the changelog.]
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Signed-off-by: NeilBrown <neilb@suse.de>
This commit is contained in:
Oleg Nesterov 2014-02-06 03:42:45 +05:30 committed by NeilBrown
parent 1877db7558
commit 789b5e0315
1 changed files with 45 additions and 47 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

92
drivers/md/raid5.c
View File

@ -5514,23 +5514,43 @@ raid5_size(struct mddev *mddev, sector_t sectors, int raid_disks)
return sectors * (raid_disks - conf->max_degraded);
}
static void free_scratch_buffer(struct r5conf *conf, struct raid5_percpu *percpu)
{
safe_put_page(percpu->spare_page);
kfree(percpu->scribble);
percpu->spare_page = NULL;
percpu->scribble = NULL;
}
static int alloc_scratch_buffer(struct r5conf *conf, struct raid5_percpu *percpu)
{
if (conf->level == 6 && !percpu->spare_page)
percpu->spare_page = alloc_page(GFP_KERNEL);
if (!percpu->scribble)
percpu->scribble = kmalloc(conf->scribble_len, GFP_KERNEL);
if (!percpu->scribble || (conf->level == 6 && !percpu->spare_page)) {
free_scratch_buffer(conf, percpu);
return -ENOMEM;
}
return 0;
}
static void raid5_free_percpu(struct r5conf *conf)
{
struct raid5_percpu *percpu;
unsigned long cpu;
if (!conf->percpu)
return;
get_online_cpus();
for_each_possible_cpu(cpu) {
percpu = per_cpu_ptr(conf->percpu, cpu);
safe_put_page(percpu->spare_page);
kfree(percpu->scribble);
}
#ifdef CONFIG_HOTPLUG_CPU
unregister_cpu_notifier(&conf->cpu_notify);
#endif
get_online_cpus();
for_each_possible_cpu(cpu)
free_scratch_buffer(conf, per_cpu_ptr(conf->percpu, cpu));
put_online_cpus();
free_percpu(conf->percpu);
@ -5557,15 +5577,7 @@ static int raid456_cpu_notify(struct notifier_block *nfb, unsigned long action,
switch (action) {
case CPU_UP_PREPARE:
case CPU_UP_PREPARE_FROZEN:
if (conf->level == 6 && !percpu->spare_page)
percpu->spare_page = alloc_page(GFP_KERNEL);
if (!percpu->scribble)
percpu->scribble = kmalloc(conf->scribble_len, GFP_KERNEL);
if (!percpu->scribble ||
(conf->level == 6 && !percpu->spare_page)) {
safe_put_page(percpu->spare_page);
kfree(percpu->scribble);
if (alloc_scratch_buffer(conf, percpu)) {
pr_err("%s: failed memory allocation for cpu%ld\n",
__func__, cpu);
return notifier_from_errno(-ENOMEM);
@ -5573,10 +5585,7 @@ static int raid456_cpu_notify(struct notifier_block *nfb, unsigned long action,
break;
case CPU_DEAD:
case CPU_DEAD_FROZEN:
safe_put_page(percpu->spare_page);
kfree(percpu->scribble);
percpu->spare_page = NULL;
percpu->scribble = NULL;
free_scratch_buffer(conf, per_cpu_ptr(conf->percpu, cpu));
break;
default:
break;
@ -5588,40 +5597,29 @@ static int raid456_cpu_notify(struct notifier_block *nfb, unsigned long action,
static int raid5_alloc_percpu(struct r5conf *conf)
{
unsigned long cpu;
struct page *spare_page;
struct raid5_percpu __percpu *allcpus;
void *scribble;
int err;
int err = 0;
allcpus = alloc_percpu(struct raid5_percpu);
if (!allcpus)
conf->percpu = alloc_percpu(struct raid5_percpu);
if (!conf->percpu)
return -ENOMEM;
conf->percpu = allcpus;
get_online_cpus();
err = 0;
for_each_present_cpu(cpu) {
if (conf->level == 6) {
spare_page = alloc_page(GFP_KERNEL);
if (!spare_page) {
err = -ENOMEM;
break;
}
per_cpu_ptr(conf->percpu, cpu)->spare_page = spare_page;
}
scribble = kmalloc(conf->scribble_len, GFP_KERNEL);
if (!scribble) {
err = -ENOMEM;
break;
}
per_cpu_ptr(conf->percpu, cpu)->scribble = scribble;
}
#ifdef CONFIG_HOTPLUG_CPU
conf->cpu_notify.notifier_call = raid456_cpu_notify;
conf->cpu_notify.priority = 0;
if (err == 0)
err = register_cpu_notifier(&conf->cpu_notify);
err = register_cpu_notifier(&conf->cpu_notify);
if (err)
return err;
#endif
get_online_cpus();
for_each_present_cpu(cpu) {
err = alloc_scratch_buffer(conf, per_cpu_ptr(conf->percpu, cpu));
if (err) {
pr_err("%s: failed memory allocation for cpu%ld\n",
__func__, cpu);
break;
}
}
put_online_cpus();
return err;