From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from cn.fujitsu.com ([222.73.24.84]:53797 "EHLO song.cn.fujitsu.com" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1752739Ab3ACBsI (ORCPT ); Wed, 2 Jan 2013 20:48:08 -0500 Message-ID: <50E4E325.6050203@cn.fujitsu.com> Date: Thu, 03 Jan 2013 09:47:17 +0800 From: Lin Feng MIME-Version: 1.0 To: bhelgaas@google.com CC: Lin Feng , linux-pci@vger.kernel.org, izumi.taku@jp.fujitsu.com, Yinghai Lu , Jiang Liu , rafael.j.wysocki@intel.com, achiang@hp.com, gregkh@linuxfoundation.org Subject: Re: [PATCH] pci-sysfs: replace mutex_lock with mutex_trylock to avoid potential deadlock situation References: <1356594177-29453-1-git-send-email-linfeng@cn.fujitsu.com> In-Reply-To: <1356594177-29453-1-git-send-email-linfeng@cn.fujitsu.com> Content-Type: text/plain; charset=UTF-8 Sender: linux-pci-owner@vger.kernel.org List-ID: Hi all, Sorry for making noise here. Is there anyone interested in this problem, any comments? thanks, linfeng On 12/27/2012 03:42 PM, Lin Feng 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 firstly 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*. > > The circumvented approach is to avoid manipulating(remove/scan) the pci-tree at > the same time. If we find someone else is manipulating the pci-tree we simply > abort current operation without touching the pci-tree concurrently. > > *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: > [] schedule+0x29/0x70 > [] schedule_preempt_disabled+0xe/0x10 > [] __mutex_lock_slowpath+0xd3/0x150 > [] mutex_lock+0x2b/0x50 > [] dev_rescan_store+0x5c/0x80 > [] dev_attr_store+0x20/0x30 > [] sysfs_write_file+0xef/0x170 > [] vfs_write+0xc8/0x190 > [] sys_write+0x51/0x90 > [] 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: > [] schedule+0x29/0x70 > [] schedule_preempt_disabled+0xe/0x10 > [] __mutex_lock_slowpath+0xd3/0x150 > [] mutex_lock+0x2b/0x50 > [] dev_rescan_store+0x5c/0x80 > [] dev_attr_store+0x20/0x30 > [] sysfs_write_file+0xef/0x170 > [] vfs_write+0xc8/0x190 > [] sys_write+0x51/0x90 > [] 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: > [] schedule+0x29/0x70 > [] schedule_timeout+0x19d/0x220 > [] ? __slab_free+0x1f2/0x2f0 > [] wait_for_common+0x11e/0x190 > [] ? try_to_wake_up+0x2c0/0x2c0 > [] wait_for_completion+0x1d/0x20 > [] sysfs_addrm_finish+0xb8/0xd0 > [] ? sysfs_schedule_callback+0x1e0/0x1e0 > [] sysfs_hash_and_remove+0x60/0xb0 > [] sysfs_remove_file+0x39/0x50 > [] device_remove_file+0x17/0x20 > [] bus_remove_device+0xdc/0x180 > [] device_del+0x120/0x1d0 > [] device_unregister+0x22/0x60 > [] pci_stop_bus_device+0x94/0xa0 > [] pci_stop_bus_device+0x40/0xa0 > [] pci_stop_bus_device+0x40/0xa0 > [] pci_stop_bus_device+0x40/0xa0 > [] pci_stop_and_remove_bus_device+0x16/0x30 > [] remove_callback+0x29/0x40 > [] sysfs_schedule_callback_work+0x24/0x70 > [] process_one_work+0x179/0x4b0 > [] worker_thread+0x12e/0x330 > [] ? manage_workers+0x110/0x110 > [] kthread+0x9e/0xb0 > [] kernel_thread_helper+0x4/0x10 > [] ? kthread_freezable_should_stop+0x70/0x70 > [] ? gs_change+0x13/0x13 > > Reported-by: Taku Izumi > Signed-off-by: Lin Feng > Signed-off-by: Gu Zheng > --- > drivers/pci/pci-sysfs.c | 42 ++++++++++++++++++++++++++---------------- > 1 files changed, 26 insertions(+), 16 deletions(-) > > diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c > index 05b78b1..d2efbb0 100644 > --- a/drivers/pci/pci-sysfs.c > +++ b/drivers/pci/pci-sysfs.c > @@ -295,10 +295,13 @@ static ssize_t bus_rescan_store(struct bus_type *bus, const char *buf, > 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 (mutex_trylock(&pci_remove_rescan_mutex)) { > + while ((b = pci_find_next_bus(b)) != NULL) > + pci_rescan_bus(b); > + mutex_unlock(&pci_remove_rescan_mutex); > + } else { > + return 0; > + } > } > return count; > } > @@ -319,9 +322,12 @@ dev_rescan_store(struct device *dev, struct device_attribute *attr, > return -EINVAL; > > if (val) { > - mutex_lock(&pci_remove_rescan_mutex); > - pci_rescan_bus(pdev->bus); > - mutex_unlock(&pci_remove_rescan_mutex); > + if (mutex_trylock(&pci_remove_rescan_mutex)) { > + pci_rescan_bus(pdev->bus); > + mutex_unlock(&pci_remove_rescan_mutex); > + } else { > + return 0; > + } > } > return count; > } > @@ -330,9 +336,10 @@ static void remove_callback(struct device *dev) > { > struct pci_dev *pdev = to_pci_dev(dev); > > - mutex_lock(&pci_remove_rescan_mutex); > - pci_stop_and_remove_bus_device(pdev); > - mutex_unlock(&pci_remove_rescan_mutex); > + if (mutex_trylock(&pci_remove_rescan_mutex)) { > + pci_stop_and_remove_bus_device(pdev); > + mutex_unlock(&pci_remove_rescan_mutex); > + } > } > > static ssize_t > @@ -366,12 +373,15 @@ dev_bus_rescan_store(struct device *dev, struct device_attribute *attr, > 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 (mutex_trylock(&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); > + } else { > + return 0; > + } > } > return count; > } >