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.
Yeah, I also guess this is a wrong detection, but I'm not familiar with this filed.
If it is really so, the lockdep guys maybe need to fix it, rather than altering an overkill
solution to accommodate it. What's your opinion?
In fact, I think "[PATCH] driver core / ACPI: Avoid device removal locking problems" is
a good solution.:)
Regards,
Gu
>
>>> [<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.
>
> 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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