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! :) Best regards, Gu 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
