On 08/01/2013 07:08 AM, Bjorn Helgaas wrote: > On Thu, May 9, 2013 at 10:53 AM, Bjorn Helgaas <bhelgaas@xxxxxxxxxx> wrote: >> On Thu, May 9, 2013 at 3:41 AM, Gu Zheng <guz.fnst@xxxxxxxxxxxxxx> wrote: >>> Hi Bjorn, >>> Very sorry to disturb you. This patch was sent a long time ago, but we have not get >>> any feedback until now. >>> It is used to fix a potential deadlock situation when doing pci-hotplug via pci-sysfs. >>> In the first version we sent: >>> https://patchwork.kernel.org/patch/1912351/ >>> replaced mutex_lock with mutex_trylock to avoid potential deadlock situation, but you suggested >>> that using a workqueue to queue these routines seems a good way to avoid the deadlock situation, >>> and this patch was followed your suggestion, can your split a while to review it? Or is there any >>> better way to fix this issue? Any comments is welcome! :) >> >> No problem, thanks for reminding me about this. I hadn't actually >> forgotten about this patch, but it does seem like it's tangled up with >> the whole pci_bus and pci_dev reference counting situation, so I was >> hoping that if we could figure out a clean resolution to that, it >> would make it more obvious what to do here. > > Gu, can you open a bugzilla for this (or include a URL here if a > bugzilla already exists)? Please include a recipe showing how to > reproduce the problem and attach a transcript, e.g., a complete dmesg > from which the portion below was extracted. Thanks! Hi Bjorn, I filed a bugzilla about this issue, and attached some useful infos, hope this can help you.:) bugzilla url:https://bugzilla.kernel.org/show_bug.cgi?id=60672 Regards, Gu > > Bjorn > >>> On 02/06/2013 06:16 PM, Gu Zheng wrote: >>> >>>> There is a potential deadlock situation when we manipulate the pci-sysfs user >>>> interfaces from different bus hierarchy simultaneously, described as following: >>>> >>>> path1: sysfs remove device: | path2: sysfs rescan device: >>>> sysfs_schedule_callback_work() | sysfs_write_file() >>>> remove_callback() | flush_write_buffer() >>>> *1* mutex_lock(&pci_remove_rescan_mutex)|*2* sysfs_get_active(attr_sd) >>>> ... | dev_attr_store() >>>> device_remove_file() | dev_rescan_store() >>>> ... |*4* >>>> mutex_lock(&pci_remove_rescan_mutex) >>>> *3* sysfs_deactivate(sd) | ... >>>> wait_for_completion() |*5* sysfs_put_active(attr_sd) >>>> *6* mutex_unlock(&pci_remove_rescan_mutex) >>>> >>>> If path1 first holds the pci_remove_rescan_mutex at *1*, then another path >>>> called path2 actived and runs to *2* before path1 runs to *3*, we now runs >>>> to a deadlock situation: >>>> Path1 holds the mutex waiting path2 to decrease sysfs_dirent's s_active >>>> counter at *5*, but path2 is blocked at *4* when trying to get the >>>> pci_remove_rescan_mutex. The mutex won't be put by path1 until it reach >>>> *6*, but it's now blocked at *3*. >>>> >>>> Under the suggestion of Bjorn, and base on Yinghai Lu's patch: >>>> http://git.kernel.org/?p=linux/kernel/git/yinghai/linux-yinghai.git;a=commitdiff;h=277df390baeab7ba6aa136356b677a096c890c0c >>>> >>>> The circumvent approach is queuing the sysfs rescan routine into workqueue just >>>> like removal to avoid manipulating(remove/scan) the pci-tree at the same time. >>>> >>>> >>>> *dmesg ifno*: >>>> (snip) >>>> 1000e 0000:1c:00.0: eth9: Intel(R) PRO/1000 Network Connection >>>> sd 13:2:0:0: [sdb] Attached SCSI disk >>>> e1000e 0000:1c:00.0: eth9: MAC: 0, PHY: 4, PBA No: D50228-005 >>>> e1000e 0000:1c:00.1: Disabling ASPM L1 >>>> e1000e 0000:1c:00.1: Interrupt Throttling Rate (ints/sec) set to dynamic >>>> conservative mode >>>> e1000e 0000:1c:00.1: irq 143 for MSI/MSI-X >>>> e1000e 0000:1c:00.1: eth10: (PCI Express:2.5GT/s:Width x4) 00:15:17:cd:96:bf >>>> e1000e 0000:1c:00.1: eth10: Intel(R) PRO/1000 Network Connection >>>> e1000e 0000:1c:00.1: eth10: MAC: 0, PHY: 4, PBA No: D50228-005 >>>> INFO: task bash:62982 blocked for more than 120 seconds. >>>> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. >>>> bash D 0000000000000000 0 62982 62978 0x00000080 >>>> ffff88038b277db8 0000000000000082 ffff88038b277fd8 0000000000013940 >>>> ffff88038b276010 0000000000013940 0000000000013940 0000000000013940 >>>> ffff88038b277fd8 0000000000013940 ffff880377449e30 ffff8806e822c670 >>>> Call Trace: >>>> [<ffffffff8151ba79>] schedule+0x29/0x70 >>>> [<ffffffff8151bd6e>] schedule_preempt_disabled+0xe/0x10 >>>> [<ffffffff8151a4e3>] __mutex_lock_slowpath+0xd3/0x150 >>>> [<ffffffff8151a3eb>] mutex_lock+0x2b/0x50 >>>> [<ffffffff812821dc>] dev_rescan_store+0x5c/0x80 >>>> [<ffffffff81341800>] dev_attr_store+0x20/0x30 >>>> [<ffffffff811e3eef>] sysfs_write_file+0xef/0x170 >>>> [<ffffffff81173d08>] vfs_write+0xc8/0x190 >>>> [<ffffffff81173ed1>] sys_write+0x51/0x90 >>>> [<ffffffff81524b29>] system_call_fastpath+0x16/0x1b >>>> INFO: task bash:64141 blocked for more than 120 seconds. >>>> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. >>>> bash D ffffffff81610460 0 64141 64136 0x00000080 >>>> ffff8803540e9db8 0000000000000086 ffff8803540e9fd8 0000000000013940 >>>> ffff8803540e8010 0000000000013940 0000000000013940 0000000000013940 >>>> ffff8803540e9fd8 0000000000013940 ffff8807db338a10 ffff8806f09abc60 >>>> Call Trace: >>>> [<ffffffff8151ba79>] schedule+0x29/0x70 >>>> [<ffffffff8151bd6e>] schedule_preempt_disabled+0xe/0x10 >>>> [<ffffffff8151a4e3>] __mutex_lock_slowpath+0xd3/0x150 >>>> [<ffffffff8151a3eb>] mutex_lock+0x2b/0x50 >>>> [<ffffffff812821dc>] dev_rescan_store+0x5c/0x80 >>>> [<ffffffff81341800>] dev_attr_store+0x20/0x30 >>>> [<ffffffff811e3eef>] sysfs_write_file+0xef/0x170 >>>> [<ffffffff81173d08>] vfs_write+0xc8/0x190 >>>> [<ffffffff81173ed1>] sys_write+0x51/0x90 >>>> [<ffffffff81524b29>] system_call_fastpath+0x16/0x1b >>>> INFO: task kworker/u:3:64451 blocked for more than 120 seconds. >>>> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. >>>> kworker/u:3 D ffffffff81610460 0 64451 2 0x00000080 >>>> ffff8807d51b7a30 0000000000000046 ffff8807d51b7fd8 0000000000013940 >>>> ffff8807d51b6010 0000000000013940 0000000000013940 0000000000013940 >>>> ffff8807d51b7fd8 0000000000013940 ffff8807db339420 ffff88037744b250 >>>> Call Trace: >>>> [<ffffffff8151ba79>] schedule+0x29/0x70 >>>> [<ffffffff81519ded>] schedule_timeout+0x19d/0x220 >>>> [<ffffffff81165f92>] ? __slab_free+0x1f2/0x2f0 >>>> [<ffffffff8151b8fe>] wait_for_common+0x11e/0x190 >>>> [<ffffffff8108a6e0>] ? try_to_wake_up+0x2c0/0x2c0 >>>> [<ffffffff8151ba4d>] wait_for_completion+0x1d/0x20 >>>> [<ffffffff811e53e8>] sysfs_addrm_finish+0xb8/0xd0 >>>> [<ffffffff811e4320>] ? sysfs_schedule_callback+0x1e0/0x1e0 >>>> [<ffffffff811e33f0>] sysfs_hash_and_remove+0x60/0xb0 >>>> [<ffffffff811e43c9>] sysfs_remove_file+0x39/0x50 >>>> [<ffffffff81342cb7>] device_remove_file+0x17/0x20 >>>> [<ffffffff8134505c>] bus_remove_device+0xdc/0x180 >>>> [<ffffffff81342eb0>] device_del+0x120/0x1d0 >>>> [<ffffffff81342f82>] device_unregister+0x22/0x60 >>>> [<ffffffff8127ade4>] pci_stop_bus_device+0x94/0xa0 >>>> [<ffffffff8127ad90>] pci_stop_bus_device+0x40/0xa0 >>>> [<ffffffff8127ad90>] pci_stop_bus_device+0x40/0xa0 >>>> [<ffffffff8127ad90>] pci_stop_bus_device+0x40/0xa0 >>>> [<ffffffff8127af66>] pci_stop_and_remove_bus_device+0x16/0x30 >>>> [<ffffffff81282359>] remove_callback+0x29/0x40 >>>> [<ffffffff811e4344>] sysfs_schedule_callback_work+0x24/0x70 >>>> [<ffffffff81070009>] process_one_work+0x179/0x4b0 >>>> [<ffffffff8107210e>] worker_thread+0x12e/0x330 >>>> [<ffffffff81071fe0>] ? manage_workers+0x110/0x110 >>>> [<ffffffff8107705e>] kthread+0x9e/0xb0 >>>> [<ffffffff81525bc4>] kernel_thread_helper+0x4/0x10 >>>> [<ffffffff81076fc0>] ? kthread_freezable_should_stop+0x70/0x70 >>>> [<ffffffff81525bc0>] ? gs_change+0x13/0x13 >>>> >>>> >>>> Signed-off-by: Yinghai Lu <yinghai@xxxxxxxxxx> >>>> Signed-off-by: Gu Zheng <guz.fnst@xxxxxxxxxxxxxx> >>>> Signed-off-by: Lin Feng <linfeng@xxxxxxxxxxxxxx> >>>> --- >>>> drivers/pci/pci-sysfs.c | 92 +++++++++++++++++++++++++++++++++-------------- >>>> 1 files changed, 65 insertions(+), 27 deletions(-) >>>> >>>> diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c >>>> index 9c6e9bb..e66b498 100644 >>>> --- a/drivers/pci/pci-sysfs.c >>>> +++ b/drivers/pci/pci-sysfs.c >>>> @@ -285,21 +285,34 @@ msi_bus_store(struct device *dev, struct device_attribute >>>> *attr, >>>> } >>>> >>>> static DEFINE_MUTEX(pci_remove_rescan_mutex); >>>> + >>>> +static void bus_rescan_callback(struct device *dev) >>>> +{ >>>> + struct pci_bus *b = NULL; >>>> + >>>> + mutex_lock(&pci_remove_rescan_mutex); >>>> + while ((b = pci_find_next_bus(b)) != NULL) >>>> + pci_rescan_bus(b); >>>> + mutex_unlock(&pci_remove_rescan_mutex); >>>> +} >>>> + >>>> static ssize_t bus_rescan_store(struct bus_type *bus, const char *buf, >>>> size_t count) >>>> { >>>> + int err; >>>> unsigned long val; >>>> - struct pci_bus *b = NULL; >>>> + struct device *dev = bus->dev_root; >>>> >>>> if (strict_strtoul(buf, 0, &val) < 0) >>>> return -EINVAL; >>>> >>>> - if (val) { >>>> - mutex_lock(&pci_remove_rescan_mutex); >>>> - while ((b = pci_find_next_bus(b)) != NULL) >>>> - pci_rescan_bus(b); >>>> - mutex_unlock(&pci_remove_rescan_mutex); >>>> - } >>>> + if (!val) >>>> + return count; >>>> + >>>> + err = device_schedule_callback(dev, bus_rescan_callback); >>>> + if (err) >>>> + return err; >>>> + >>>> return count; >>>> } >>>> >>>> @@ -308,21 +321,32 @@ struct bus_attribute pci_bus_attrs[] = { >>>> __ATTR_NULL >>>> }; >>>> >>>> +static void dev_rescan_callback(struct device *dev) >>>> +{ >>>> + struct pci_dev *pdev = to_pci_dev(dev); >>>> + >>>> + if (pdev->is_added) { >>>> + mutex_lock(&pci_remove_rescan_mutex); >>>> + pci_rescan_bus(pdev->bus); >>>> + mutex_unlock(&pci_remove_rescan_mutex); >>>> + } >>>> +} >>>> + >>>> static ssize_t >>>> dev_rescan_store(struct device *dev, struct device_attribute *attr, >>>> const char *buf, size_t count) >>>> { >>>> + int err; >>>> unsigned long val; >>>> - struct pci_dev *pdev = to_pci_dev(dev); >>>> >>>> if (strict_strtoul(buf, 0, &val) < 0) >>>> return -EINVAL; >>>> >>>> - if (val) { >>>> - mutex_lock(&pci_remove_rescan_mutex); >>>> - pci_rescan_bus(pdev->bus); >>>> - mutex_unlock(&pci_remove_rescan_mutex); >>>> - } >>>> + if (!val) >>>> + return count; >>>> + err = device_schedule_callback(dev, dev_rescan_callback); >>>> + if (err) >>>> + return err; >>>> return count; >>>> } >>>> >>>> @@ -339,7 +363,7 @@ static ssize_t >>>> remove_store(struct device *dev, struct device_attribute *dummy, >>>> const char *buf, size_t count) >>>> { >>>> - int ret = 0; >>>> + int err; >>>> unsigned long val; >>>> >>>> if (strict_strtoul(buf, 0, &val) < 0) >>>> @@ -348,31 +372,45 @@ remove_store(struct device *dev, struct device_attribute >>>> *dummy, >>>> /* An attribute cannot be unregistered by one of its own methods, >>>> * so we have to use this roundabout approach. >>>> */ >>>> - if (val) >>>> - ret = device_schedule_callback(dev, remove_callback); >>>> - if (ret) >>>> - count = ret; >>>> + if (!val) >>>> + return count; >>>> + >>>> + err = device_schedule_callback(dev, remove_callback); >>>> + if (err) >>>> + return err; >>>> + >>>> return count; >>>> } >>>> >>>> +static void dev_bus_rescan_callback(struct device *dev) >>>> +{ >>>> + struct pci_bus *bus = to_pci_bus(dev); >>>> + >>>> + mutex_lock(&pci_remove_rescan_mutex); >>>> + if (!pci_is_root_bus(bus) && list_empty(&bus->devices)) >>>> + pci_rescan_bus_bridge_resize(bus->self); >>>> + else >>>> + pci_rescan_bus(bus); >>>> + mutex_unlock(&pci_remove_rescan_mutex); >>>> +} >>>> + >>>> static ssize_t >>>> dev_bus_rescan_store(struct device *dev, struct device_attribute *attr, >>>> const char *buf, size_t count) >>>> { >>>> + int err; >>>> unsigned long val; >>>> - struct pci_bus *bus = to_pci_bus(dev); >>>> >>>> if (strict_strtoul(buf, 0, &val) < 0) >>>> return -EINVAL; >>>> >>>> - if (val) { >>>> - mutex_lock(&pci_remove_rescan_mutex); >>>> - if (!pci_is_root_bus(bus) && list_empty(&bus->devices)) >>>> - pci_rescan_bus_bridge_resize(bus->self); >>>> - else >>>> - pci_rescan_bus(bus); >>>> - mutex_unlock(&pci_remove_rescan_mutex); >>>> - } >>>> + if (!val) >>>> + return count; >>>> + >>>> + err = device_schedule_callback(dev, dev_bus_rescan_callback); >>>> + if (err) >>>> + return err; >>>> + >>>> return count; >>>> } >>>> >>>> -- 1.7.7 >>>> >>>> -- >>>> To unsubscribe from this list: send the line "unsubscribe linux-pci" in >>>> the body of a message to majordomo@xxxxxxxxxxxxxxx >>>> More majordomo info at http://vger.kernel.org/majordomo-info.html >>>> >>> >>> >>> -- >>> To unsubscribe from this list: send the line "unsubscribe linux-pci" in >>> the body of a message to majordomo@xxxxxxxxxxxxxxx >>> More 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