Hi Rafael,
On 08/26/2013 10:43 PM, Rafael J. Wysocki wrote:
> On Monday, August 26, 2013 02:42:09 PM Rafael J. Wysocki wrote:
>> On Monday, August 26, 2013 11:13:13 AM Gu Zheng wrote:
>>> Hi Rafael,
>>
>> Hi,
>>
>>> On 08/26/2013 04:09 AM, Rafael J. Wysocki wrote:
>>>
>>>> From: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
>>>>
>>>> There are two mutexes, device_hotplug_lock and acpi_scan_lock, held
>>>> around the acpi_bus_trim() call in acpi_scan_hot_remove() which
>>>> generally removes devices (it removes ACPI device objects at least,
>>>> but it may also remove "physical" device objects through .detach()
>>>> callbacks of ACPI scan handlers). Thus, potentially, device sysfs
>>>> attributes are removed under these locks and to remove those
>>>> attributes it is necessary to hold the s_active references of their
>>>> directory entries for writing.
>>>>
>>>> On the other hand, the execution of a .show() or .store() callback
>>>> from a sysfs attribute is carried out with that attribute's s_active
>>>> reference held for reading. Consequently, if any device sysfs
>>>> attribute that may be removed from within acpi_scan_hot_remove()
>>>> through acpi_bus_trim() has a .store() or .show() callback which
>>>> acquires either acpi_scan_lock or device_hotplug_lock, the execution
>>>> of that callback may deadlock with the removal of the attribute.
>>>> [Unfortunately, the "online" device attribute of CPUs and memory
>>>> blocks and the "eject" attribute of ACPI device objects are affected
>>>> by this issue.]
>>>>
>>>> To avoid those deadlocks introduce a new protection mechanism that
>>>> can be used by the device sysfs attributes in question. Namely,
>>>> if a device sysfs attribute's .store() or .show() callback routine
>>>> is about to acquire device_hotplug_lock or acpi_scan_lock, it can
>>>> first execute read_lock_device_remove() and return an error code if
>>>> that function returns false. If true is returned, the lock in
>>>> question may be acquired and read_unlock_device_remove() must be
>>>> called. [This mechanism is implemented by means of an additional
>>>> rwsem in drivers/base/core.c.]
>>>>
>>>> Make the affected sysfs attributes in the driver core and ACPI core
>>>> use read_lock_device_remove() and read_unlock_device_remove() as
>>>> described above.
>>>>
>>>> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
>>>> Reported-by: Gu Zheng <guz.fnst@xxxxxxxxxxxxxx>
>>>
>>> I'm sorry to forget to mention that the original reporter is
>>> Yasuaki Ishimatsu <isimatu.yasuaki@xxxxxxxxxxxxxx>. I continued
>>> the investigation and found more issues.
>>>
>>> We tested this patch on kernel 3.11-rc6, but it seems that the
>>> issue is still there. Detail info as following.
>>
>> Well, taking pm_mutex under acpi_scan_lock (trace #2) is a bad idea anyway,
>> because we'll need to take acpi_scan_lock during system suspend for PCI hot
>> remove to work and that's under pm_mutex. So I wonder if we can simply
>> drop the system sleep locking from lock/unlock_memory_hotplug(). But that's
>> a side note, because dropping it won't help here.
>>
>> Now ->
>>
>>> ======================================================
>>> [ INFO: possible circular locking dependency detected ]
>>> 3.11.0-rc6-lockdebug-refea+ #162 Tainted: GF
>>> -------------------------------------------------------
>>> kworker/0:2/754 is trying to acquire lock:
>>> (s_active#73){++++.+}, at: [<ffffffff8121062b>] sysfs_addrm_finish+0x3b/0x70
>>>
>>> but task is already holding lock:
>>> (mem_sysfs_mutex){+.+.+.}, at: [<ffffffff813b949d>] remove_memory_block+0x1d/0xa0
>>>
>>> which lock already depends on the new lock.
>>>
>>>
>>> the existing dependency chain (in reverse order) is:
>>>
>>> -> #4 (mem_sysfs_mutex){+.+.+.}:
>>> [<ffffffff810ba88c>] validate_chain+0x70c/0x870
>>> [<ffffffff810bad5f>] __lock_acquire+0x36f/0x5f0
>>> [<ffffffff810bb080>] lock_acquire+0xa0/0x130
>>> [<ffffffff8159781b>] mutex_lock_nested+0x7b/0x3b0
>>> [<ffffffff813b9361>] add_memory_section+0x51/0x150
>>> [<ffffffff813b947b>] register_new_memory+0x1b/0x20
>>> [<ffffffff81590d21>] __add_pages+0x111/0x120
>>> [<ffffffff81041224>] arch_add_memory+0x64/0xf0
>>> [<ffffffff81590e07>] add_memory+0xd7/0x1e0
>>> [<ffffffff81347db4>] acpi_memory_enable_device+0x77/0x12b
>>> [<ffffffff8134801e>] acpi_memory_device_add+0x18f/0x198
>>> [<ffffffff8131aa5a>] acpi_bus_device_attach+0x9a/0x100
>>> [<ffffffff8133666d>] acpi_ns_walk_namespace+0xbe/0x17d
>>> [<ffffffff81336b03>] acpi_walk_namespace+0x8a/0xc4
>>> [<ffffffff8131c126>] acpi_bus_scan+0x91/0x9c
>>> [<ffffffff8131c1af>] acpi_scan_bus_device_check+0x7e/0x10f
>>> [<ffffffff8131c253>] acpi_scan_device_check+0x13/0x15
>>> [<ffffffff81315dac>] acpi_os_execute_deferred+0x27/0x34
>>> [<ffffffff8106bec8>] process_one_work+0x1e8/0x560
>>> [<ffffffff8106d0a0>] worker_thread+0x120/0x3a0
>>> [<ffffffff81073b5e>] kthread+0xee/0x100
>>> [<ffffffff815a605c>] ret_from_fork+0x7c/0xb0
>>>
>>> -> #3 (pm_mutex){+.+.+.}:
>>> [<ffffffff810ba88c>] validate_chain+0x70c/0x870
>>> [<ffffffff810bad5f>] __lock_acquire+0x36f/0x5f0
>>> [<ffffffff810bb080>] lock_acquire+0xa0/0x130
>>> [<ffffffff8159781b>] mutex_lock_nested+0x7b/0x3b0
>>> [<ffffffff81188795>] lock_memory_hotplug+0x35/0x40
>>> [<ffffffff81590d5f>] add_memory+0x2f/0x1e0
>>> [<ffffffff81347db4>] acpi_memory_enable_device+0x77/0x12b
>>> [<ffffffff8134801e>] acpi_memory_device_add+0x18f/0x198
>>> [<ffffffff8131aa5a>] acpi_bus_device_attach+0x9a/0x100
>>> [<ffffffff8133666d>] acpi_ns_walk_namespace+0xbe/0x17d
>>> [<ffffffff81336b03>] acpi_walk_namespace+0x8a/0xc4
>>> [<ffffffff8131c126>] acpi_bus_scan+0x91/0x9c
>>> [<ffffffff81d39862>] acpi_scan_init+0x66/0x15a
>>> [<ffffffff81d397a0>] acpi_init+0xa1/0xbb
>>> [<ffffffff810002c2>] do_one_initcall+0xf2/0x1a0
>>> [<ffffffff81d018da>] do_basic_setup+0x9d/0xbb
>>> [<ffffffff81d01b02>] kernel_init_freeable+0x20a/0x28a
>>> [<ffffffff8158f20e>] kernel_init+0xe/0xf0
>>> [<ffffffff815a605c>] ret_from_fork+0x7c/0xb0
>>>
>>> -> #2 (mem_hotplug_mutex){+.+.+.}:
>>> [<ffffffff810ba88c>] validate_chain+0x70c/0x870
>>> [<ffffffff810bad5f>] __lock_acquire+0x36f/0x5f0
>>> [<ffffffff810bb080>] lock_acquire+0xa0/0x130
>>> [<ffffffff8159781b>] mutex_lock_nested+0x7b/0x3b0
>>> [<ffffffff81188777>] lock_memory_hotplug+0x17/0x40
>>> [<ffffffff81590d5f>] add_memory+0x2f/0x1e0
>>> [<ffffffff81347db4>] acpi_memory_enable_device+0x77/0x12b
>>> [<ffffffff8134801e>] acpi_memory_device_add+0x18f/0x198
>>> [<ffffffff8131aa5a>] acpi_bus_device_attach+0x9a/0x100
>>> [<ffffffff8133666d>] acpi_ns_walk_namespace+0xbe/0x17d
>>> [<ffffffff81336b03>] acpi_walk_namespace+0x8a/0xc4
>>> [<ffffffff8131c126>] acpi_bus_scan+0x91/0x9c
>>> [<ffffffff8131c1af>] acpi_scan_bus_device_check+0x7e/0x10f
>>> [<ffffffff8131c253>] acpi_scan_device_check+0x13/0x15
>>> [<ffffffff81315dac>] acpi_os_execute_deferred+0x27/0x34
>>> [<ffffffff8106bec8>] process_one_work+0x1e8/0x560
>>> [<ffffffff8106d0a0>] worker_thread+0x120/0x3a0
>>> [<ffffffff81073b5e>] kthread+0xee/0x100
>>> [<ffffffff815a605c>] ret_from_fork+0x7c/0xb0
>>>
>>> -> #1 (device_hotplug_lock){+.+.+.}:
>>> [<ffffffff810ba88c>] validate_chain+0x70c/0x870
>>> [<ffffffff810bad5f>] __lock_acquire+0x36f/0x5f0
>>> [<ffffffff810bb080>] lock_acquire+0xa0/0x130
>>> [<ffffffff8159781b>] mutex_lock_nested+0x7b/0x3b0
>>> [<ffffffff813a16e7>] lock_device_hotplug+0x17/0x20
>>
>> -> we should have grabbed device_remove_rwsem for reading here with the patch
>> applied, which means that -->
>>
>>> [<ffffffff813a2553>] show_online+0x33/0x80
>>> [<ffffffff813a1ce7>] dev_attr_show+0x27/0x50
>>> [<ffffffff8120ee94>] fill_read_buffer+0x74/0x100
>>> [<ffffffff8120efcc>] sysfs_read_file+0xac/0xe0
>>> [<ffffffff81195d21>] vfs_read+0xb1/0x130
>>> [<ffffffff81196232>] SyS_read+0x62/0xb0
>>> [<ffffffff815a6102>] system_call_fastpath+0x16/0x1b
>>>
>>> -> #0 (s_active#73){++++.+}:
>>> [<ffffffff810ba148>] check_prev_add+0x598/0x5d0
>>> [<ffffffff810ba88c>] validate_chain+0x70c/0x870
>>> [<ffffffff810bad5f>] __lock_acquire+0x36f/0x5f0
>>> [<ffffffff810bb080>] lock_acquire+0xa0/0x130
>>> [<ffffffff8120fed7>] sysfs_deactivate+0x157/0x1c0
>>> [<ffffffff8121062b>] sysfs_addrm_finish+0x3b/0x70
>>> [<ffffffff8120e280>] sysfs_hash_and_remove+0x60/0xb0
>>> [<ffffffff8120f2a9>] sysfs_remove_file+0x39/0x50
>>> [<ffffffff813a2977>] device_remove_file+0x17/0x20
>>> [<ffffffff813a29aa>] device_remove_attrs+0x2a/0xe0
>>> [<ffffffff813a2b8b>] device_del+0x12b/0x1f0
>>> [<ffffffff813a2c72>] device_unregister+0x22/0x60
>>> [<ffffffff813b94ed>] remove_memory_block+0x6d/0xa0
>>> [<ffffffff813b953f>] unregister_memory_section+0x1f/0x30
>>> [<ffffffff81189468>] __remove_pages+0xc8/0x150
>>> [<ffffffff8158f994>] arch_remove_memory+0x94/0xd0
>>> [<ffffffff81590bef>] remove_memory+0x6f/0x90
>>> [<ffffffff81347ccc>] acpi_memory_remove_memory+0x7e/0xa3
>>> [<ffffffff81347d18>] acpi_memory_device_remove+0x27/0x33
>>> [<ffffffff8131a8a2>] acpi_bus_device_detach+0x3d/0x5e
>>> [<ffffffff81336685>] acpi_ns_walk_namespace+0xd6/0x17d
>>> [<ffffffff81336b03>] acpi_walk_namespace+0x8a/0xc4
>>> [<ffffffff8131a8f6>] acpi_bus_trim+0x33/0x7a
>>> [<ffffffff8131b4c0>] acpi_scan_hot_remove+0x160/0x281
>>
>> --> device_hotplug_lock is already held by show_online() at this point (or if
>> it is not held, that function will return -EBUSY after attempting to grab
>> device_remove_rwsem for reading), so acpi_scan_hot_remove() will wait for it
>> to be released before calling acpi_bus_trim().
>>
>> So the situation in which one thread holds s_active for reading and blocks on
>> device_hotplug_lock while another thread is holding it over device removal is
>> clearly impossible to me.
>>
>> So I'm not sure how device_hotplug_lock is still involved?
>
> Well, it is not involved, but lockdep doesn't see that anyway. Bummer.
>
>>> [<ffffffff8131b6fc>] acpi_bus_hot_remove_device+0x37/0x73
>>> [<ffffffff81315dac>] acpi_os_execute_deferred+0x27/0x34
>>> [<ffffffff8106bec8>] process_one_work+0x1e8/0x560
>>> [<ffffffff8106d0a0>] worker_thread+0x120/0x3a0
>>> [<ffffffff81073b5e>] kthread+0xee/0x100
>>> [<ffffffff815a605c>] ret_from_fork+0x7c/0xb0
>>>
>>> other info that might help us debug this:
>>>
>>> Chain exists of:
>>> s_active#73 --> pm_mutex --> mem_sysfs_mutex
>>>
>>> Possible unsafe locking scenario:
>>>
>>> CPU0 CPU1
>>> ---- ----
>>> lock(mem_sysfs_mutex);
>>> lock(pm_mutex);
>>> lock(mem_sysfs_mutex);
>>> lock(s_active#73);
>>>
>>> *** DEADLOCK ***
>
> OK, so the patch below is quick and dirty and overkill, but it should make the
> splat go away at least.
Yeah, this patch is the same as the one I attached in previous discussion threads.
It does make the splat go away, but as you said, it's a bit overkill.
Regards,
Gu
>
> Thanks,
> Rafael
>
>
> ---
> drivers/acpi/scan.c | 3 ++-
> drivers/base/core.c | 36 ++++++++++++++++++++----------------
> 2 files changed, 22 insertions(+), 17 deletions(-)
>
> Index: linux-pm/drivers/base/core.c
> ===================================================================
> --- linux-pm.orig/drivers/base/core.c
> +++ linux-pm/drivers/base/core.c
> @@ -49,6 +49,18 @@ static struct kobject *dev_kobj;
> struct kobject *sysfs_dev_char_kobj;
> struct kobject *sysfs_dev_block_kobj;
>
> +static DEFINE_MUTEX(device_hotplug_lock);
> +
> +void lock_device_hotplug(void)
> +{
> + mutex_lock(&device_hotplug_lock);
> +}
> +
> +void unlock_device_hotplug(void)
> +{
> + mutex_unlock(&device_hotplug_lock);
> +}
> +
> #ifdef CONFIG_BLOCK
> static inline int device_is_not_partition(struct device *dev)
> {
> @@ -408,9 +420,11 @@ static ssize_t show_online(struct device
> {
> bool val;
>
> - lock_device_hotplug();
> + if (!mutex_trylock(&device_hotplug_lock))
> + return -EAGAIN;
> +
> val = !dev->offline;
> - unlock_device_hotplug();
> + mutex_unlock(&device_hotplug_lock);
> return sprintf(buf, "%u\n", val);
> }
>
> @@ -424,9 +438,11 @@ static ssize_t store_online(struct devic
> if (ret < 0)
> return ret;
>
> - lock_device_hotplug();
> + if (!mutex_trylock(&device_hotplug_lock))
> + return -EAGAIN;
> +
> ret = val ? device_online(dev) : device_offline(dev);
> - unlock_device_hotplug();
> + mutex_unlock(&device_hotplug_lock);
> return ret < 0 ? ret : count;
> }
>
> @@ -1479,18 +1495,6 @@ EXPORT_SYMBOL_GPL(put_device);
> EXPORT_SYMBOL_GPL(device_create_file);
> EXPORT_SYMBOL_GPL(device_remove_file);
>
> -static DEFINE_MUTEX(device_hotplug_lock);
> -
> -void lock_device_hotplug(void)
> -{
> - mutex_lock(&device_hotplug_lock);
> -}
> -
> -void unlock_device_hotplug(void)
> -{
> - mutex_unlock(&device_hotplug_lock);
> -}
> -
> static int device_check_offline(struct device *dev, void *not_used)
> {
> int ret;
> Index: linux-pm/drivers/acpi/scan.c
> ===================================================================
> --- linux-pm.orig/drivers/acpi/scan.c
> +++ linux-pm/drivers/acpi/scan.c
> @@ -510,7 +510,8 @@ acpi_eject_store(struct device *d, struc
> if (ACPI_FAILURE(status) || !acpi_device->flags.ejectable)
> return -ENODEV;
>
> - mutex_lock(&acpi_scan_lock);
> + if (!mutex_trylock(&acpi_scan_lock))
> + return -EAGAIN;
>
> if (acpi_device->flags.eject_pending) {
> /* ACPI eject notification event. */
>
>
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