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! 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 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 majordomo info at http://vger.kernel.org/majordomo-info.html
