On Wed, Oct 30, 2013 at 06:12:27PM +0800, Gu Zheng wrote: > There is a potential deadlock situation when we manipulate pci device > (remove&rescan) via the pci-sysfs user interfaces simultaneously. > > Privious patch: > https://lkml.org/lkml/2012/12/27/10 > > Related bug reports on bugzilla: > https://bugzilla.kernel.org/show_bug.cgi?id=60672 > https://bugzilla.kernel.org/show_bug.cgi?id=60695 > > deadlock info described as following: > > *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 > > 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*. > > So we use mutex_try_lock to avoid this deadlock, and additional wait/restart_syscall > steps are used to make the fail path of try_lock more friendly to user space task. > > Signed-off-by: Gu Zheng <guz.fnst@xxxxxxxxxxxxxx> > --- > drivers/pci/pci-sysfs.c | 48 +++++++++++++++++++++++++++++++++++++++------- > 1 files changed, 40 insertions(+), 8 deletions(-) > > diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c > index 7128cfd..0dac6f4 100644 > --- a/drivers/pci/pci-sysfs.c > +++ b/drivers/pci/pci-sysfs.c > @@ -29,6 +29,7 @@ > #include <linux/slab.h> > #include <linux/vgaarb.h> > #include <linux/pm_runtime.h> > +#include <linux/delay.h> > #include "pci.h" > > static int sysfs_initialized; /* = 0 */ > @@ -285,6 +286,25 @@ msi_bus_store(struct device *dev, struct device_attribute *attr, > } > > static DEFINE_MUTEX(pci_remove_rescan_mutex); > + > +static void pci_remove_rescan_lock(void) > +{ > + mutex_lock(&pci_remove_rescan_mutex); > +} > + > +static int pci_remove_rescan_lock_sysfs(void) > +{ > + if (mutex_trylock(&pci_remove_rescan_mutex)) > + return 0; > + /* Avoid busy looping (20 ms of sleep should do). */ > + msleep(20); > + return restart_syscall(); There are very few uses of restart_syscall(). I don't believe this situation is so unusual and special that we need to use it here. > +} > + > +static void pci_remove_rescan_unlock(void) > +{ > + mutex_unlock(&pci_remove_rescan_mutex); > +} > static ssize_t bus_rescan_store(struct bus_type *bus, const char *buf, > size_t count) > { > @@ -295,10 +315,14 @@ static ssize_t bus_rescan_store(struct bus_type *bus, const char *buf, > return -EINVAL; > > if (val) { > - mutex_lock(&pci_remove_rescan_mutex); > + int ret; > + > + ret = pci_remove_rescan_lock_sysfs(); > + if (ret) > + return ret; > while ((b = pci_find_next_bus(b)) != NULL) > pci_rescan_bus(b); > - mutex_unlock(&pci_remove_rescan_mutex); > + pci_remove_rescan_unlock(); > } > return count; > } > @@ -319,9 +343,13 @@ dev_rescan_store(struct device *dev, struct device_attribute *attr, > return -EINVAL; > > if (val) { > - mutex_lock(&pci_remove_rescan_mutex); > + int ret; > + > + ret = pci_remove_rescan_lock_sysfs(); > + if (ret) > + return ret; > pci_rescan_bus(pdev->bus); > - mutex_unlock(&pci_remove_rescan_mutex); > + pci_remove_rescan_unlock(); > } > return count; > } > @@ -332,9 +360,9 @@ static void remove_callback(struct device *dev) > { > struct pci_dev *pdev = to_pci_dev(dev); > > - mutex_lock(&pci_remove_rescan_mutex); > + pci_remove_rescan_lock(); > pci_stop_and_remove_bus_device(pdev); > - mutex_unlock(&pci_remove_rescan_mutex); > + pci_remove_rescan_unlock(); > } > > static ssize_t > @@ -370,12 +398,16 @@ dev_bus_rescan_store(struct device *dev, struct device_attribute *attr, > return -EINVAL; > > if (val) { > - mutex_lock(&pci_remove_rescan_mutex); > + int ret; > + > + ret = pci_remove_rescan_lock_sysfs(); > + if (ret) > + return ret; > 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); > + pci_remove_rescan_unlock(); > } > 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
