Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756057Ab3HZOcs (ORCPT ); Mon, 26 Aug 2013 10:32:48 -0400 Received: from hydra.sisk.pl ([212.160.235.94]:35002 "EHLO hydra.sisk.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751725Ab3HZOcq (ORCPT ); Mon, 26 Aug 2013 10:32:46 -0400 From: "Rafael J. Wysocki" To: Gu Zheng Cc: ACPI Devel Maling List , Greg Kroah-Hartman , Toshi Kani , LKML , Yasuaki Ishimatsu Subject: Re: [PATCH] driver core / ACPI: Avoid device removal locking problems Date: Mon, 26 Aug 2013 16:43:26 +0200 Message-ID: <3389643.Fdir3g6c6B@vostro.rjw.lan> User-Agent: KMail/4.10.5 (Linux/3.11.0-rc6+; KDE/4.10.5; x86_64; ; ) In-Reply-To: <4785337.sqQqDSPcpL@vostro.rjw.lan> References: <1543475.L7gSB7lLAu@vostro.rjw.lan> <521AC7C9.2000408@cn.fujitsu.com> <4785337.sqQqDSPcpL@vostro.rjw.lan> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="utf-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 32228 Lines: 325 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 > > > > > > 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 > > > Reported-by: Gu Zheng > > > > I'm sorry to forget to mention that the original reporter is > > Yasuaki Ishimatsu . 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: [] sysfs_addrm_finish+0x3b/0x70 > > > > but task is already holding lock: > > (mem_sysfs_mutex){+.+.+.}, at: [] 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){+.+.+.}: > > [] validate_chain+0x70c/0x870 > > [] __lock_acquire+0x36f/0x5f0 > > [] lock_acquire+0xa0/0x130 > > [] mutex_lock_nested+0x7b/0x3b0 > > [] add_memory_section+0x51/0x150 > > [] register_new_memory+0x1b/0x20 > > [] __add_pages+0x111/0x120 > > [] arch_add_memory+0x64/0xf0 > > [] add_memory+0xd7/0x1e0 > > [] acpi_memory_enable_device+0x77/0x12b > > [] acpi_memory_device_add+0x18f/0x198 > > [] acpi_bus_device_attach+0x9a/0x100 > > [] acpi_ns_walk_namespace+0xbe/0x17d > > [] acpi_walk_namespace+0x8a/0xc4 > > [] acpi_bus_scan+0x91/0x9c > > [] acpi_scan_bus_device_check+0x7e/0x10f > > [] acpi_scan_device_check+0x13/0x15 > > [] acpi_os_execute_deferred+0x27/0x34 > > [] process_one_work+0x1e8/0x560 > > [] worker_thread+0x120/0x3a0 > > [] kthread+0xee/0x100 > > [] ret_from_fork+0x7c/0xb0 > > > > -> #3 (pm_mutex){+.+.+.}: > > [] validate_chain+0x70c/0x870 > > [] __lock_acquire+0x36f/0x5f0 > > [] lock_acquire+0xa0/0x130 > > [] mutex_lock_nested+0x7b/0x3b0 > > [] lock_memory_hotplug+0x35/0x40 > > [] add_memory+0x2f/0x1e0 > > [] acpi_memory_enable_device+0x77/0x12b > > [] acpi_memory_device_add+0x18f/0x198 > > [] acpi_bus_device_attach+0x9a/0x100 > > [] acpi_ns_walk_namespace+0xbe/0x17d > > [] acpi_walk_namespace+0x8a/0xc4 > > [] acpi_bus_scan+0x91/0x9c > > [] acpi_scan_init+0x66/0x15a > > [] acpi_init+0xa1/0xbb > > [] do_one_initcall+0xf2/0x1a0 > > [] do_basic_setup+0x9d/0xbb > > [] kernel_init_freeable+0x20a/0x28a > > [] kernel_init+0xe/0xf0 > > [] ret_from_fork+0x7c/0xb0 > > > > -> #2 (mem_hotplug_mutex){+.+.+.}: > > [] validate_chain+0x70c/0x870 > > [] __lock_acquire+0x36f/0x5f0 > > [] lock_acquire+0xa0/0x130 > > [] mutex_lock_nested+0x7b/0x3b0 > > [] lock_memory_hotplug+0x17/0x40 > > [] add_memory+0x2f/0x1e0 > > [] acpi_memory_enable_device+0x77/0x12b > > [] acpi_memory_device_add+0x18f/0x198 > > [] acpi_bus_device_attach+0x9a/0x100 > > [] acpi_ns_walk_namespace+0xbe/0x17d > > [] acpi_walk_namespace+0x8a/0xc4 > > [] acpi_bus_scan+0x91/0x9c > > [] acpi_scan_bus_device_check+0x7e/0x10f > > [] acpi_scan_device_check+0x13/0x15 > > [] acpi_os_execute_deferred+0x27/0x34 > > [] process_one_work+0x1e8/0x560 > > [] worker_thread+0x120/0x3a0 > > [] kthread+0xee/0x100 > > [] ret_from_fork+0x7c/0xb0 > > > > -> #1 (device_hotplug_lock){+.+.+.}: > > [] validate_chain+0x70c/0x870 > > [] __lock_acquire+0x36f/0x5f0 > > [] lock_acquire+0xa0/0x130 > > [] mutex_lock_nested+0x7b/0x3b0 > > [] lock_device_hotplug+0x17/0x20 > > -> we should have grabbed device_remove_rwsem for reading here with the patch > applied, which means that --> > > > [] show_online+0x33/0x80 > > [] dev_attr_show+0x27/0x50 > > [] fill_read_buffer+0x74/0x100 > > [] sysfs_read_file+0xac/0xe0 > > [] vfs_read+0xb1/0x130 > > [] SyS_read+0x62/0xb0 > > [] system_call_fastpath+0x16/0x1b > > > > -> #0 (s_active#73){++++.+}: > > [] check_prev_add+0x598/0x5d0 > > [] validate_chain+0x70c/0x870 > > [] __lock_acquire+0x36f/0x5f0 > > [] lock_acquire+0xa0/0x130 > > [] sysfs_deactivate+0x157/0x1c0 > > [] sysfs_addrm_finish+0x3b/0x70 > > [] sysfs_hash_and_remove+0x60/0xb0 > > [] sysfs_remove_file+0x39/0x50 > > [] device_remove_file+0x17/0x20 > > [] device_remove_attrs+0x2a/0xe0 > > [] device_del+0x12b/0x1f0 > > [] device_unregister+0x22/0x60 > > [] remove_memory_block+0x6d/0xa0 > > [] unregister_memory_section+0x1f/0x30 > > [] __remove_pages+0xc8/0x150 > > [] arch_remove_memory+0x94/0xd0 > > [] remove_memory+0x6f/0x90 > > [] acpi_memory_remove_memory+0x7e/0xa3 > > [] acpi_memory_device_remove+0x27/0x33 > > [] acpi_bus_device_detach+0x3d/0x5e > > [] acpi_ns_walk_namespace+0xd6/0x17d > > [] acpi_walk_namespace+0x8a/0xc4 > > [] acpi_bus_trim+0x33/0x7a > > [] 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. > > [] acpi_bus_hot_remove_device+0x37/0x73 > > [] acpi_os_execute_deferred+0x27/0x34 > > [] process_one_work+0x1e8/0x560 > > [] worker_thread+0x120/0x3a0 > > [] kthread+0xee/0x100 > > [] 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. */ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/