On Tuesday, November 26, 2013 12:13:50 PM Yinghai Lu wrote: > On Tue, Nov 26, 2013 at 11:34 AM, Yinghai Lu <ying...@kernel.org> wrote: > > On Mon, Nov 25, 2013 at 7:38 PM, Bjorn Helgaas <bhelg...@google.com> wrote: > >> On Mon, Nov 25, 2013 at 6:28 PM, Yinghai Lu <ying...@kernel.org> wrote: > >>> Mutliple removing via /sys will call pci_destroy_dev two times. > >>> > >>> | When concurent removing pci devices which are in the same pci subtree > >>> | via sysfs, such as: > >>> | echo -n 1 > /sys/bus/pci/devices/0000\:10\:00.0/remove ; echo -n 1 > > >>> | /sys/bus/pci/devices/0000\:1a\:01.0/remove > >>> | (1a:01.0 device is downstream from the 10:00.0 bridge) > >>> | > >>> | the following warning will show: > >>> | [ 1799.280918] ------------[ cut here ]------------ > >>> | [ 1799.336199] WARNING: CPU: 7 PID: 126 at lib/list_debug.c:53 > >>> __list_del_entry+0x63/0xd0() > >>> | [ 1799.433093] list_del corruption, ffff8807b4a7c000->next is > >>> LIST_POISON1 (dead000000100100) > >>> | [ 1800.276623] CPU: 7 PID: 126 Comm: kworker/u512:1 Tainted: G W > >>> 3.12.0-rc5+ #196 > >>> | [ 1800.508918] Workqueue: sysfsd sysfs_schedule_callback_work > >>> | [ 1800.574703] 0000000000000009 ffff8807adbadbd8 ffffffff8168b26c > >>> ffff8807c27d08a8 > >>> | [ 1800.663860] ffff8807adbadc28 ffff8807adbadc18 ffffffff810711dc > >>> ffff8807adbadc68 > >>> | [ 1800.753130] ffff8807b4a7c000 ffff8807b4a7c000 ffff8807ad089c00 > >>> 0000000000000000 > >>> | [ 1800.842282] Call Trace: > >>> | [ 1800.871651] [<ffffffff8168b26c>] dump_stack+0x55/0x76 > >>> | [ 1800.933301] [<ffffffff810711dc>] warn_slowpath_common+0x8c/0xc0 > >>> | [ 1801.005283] [<ffffffff810712c6>] warn_slowpath_fmt+0x46/0x50 > >>> | [ 1801.074081] [<ffffffff8135a343>] __list_del_entry+0x63/0xd0 > >>> | [ 1801.141839] [<ffffffff8135a3c1>] list_del+0x11/0x40 > >>> | [ 1801.201320] [<ffffffff813734da>] pci_remove_bus_device+0x6a/0xe0 > >>> | [ 1801.274279] [<ffffffff8137356e>] > >>> pci_stop_and_remove_bus_device+0x1e/0x30 > >>> | [ 1801.356606] [<ffffffff8137b20b>] remove_callback+0x2b/0x40 > >>> | [ 1801.423412] [<ffffffff81251848>] > >>> sysfs_schedule_callback_work+0x18/0x60 > >>> | [ 1801.503744] [<ffffffff8108eab5>] process_one_work+0x1f5/0x540 > >>> | [ 1801.573640] [<ffffffff8108ea53>] ? process_one_work+0x193/0x540 > >>> | [ 1801.645616] [<ffffffff8108f2ac>] worker_thread+0x11c/0x370 > >>> | [ 1801.712337] [<ffffffff8108f190>] ? rescuer_thread+0x350/0x350 > >>> | [ 1801.782178] [<ffffffff8109731d>] kthread+0xed/0x100 > >>> | [ 1801.841661] [<ffffffff81097230>] ? > >>> kthread_create_on_node+0x160/0x160 > >>> | [ 1801.919919] [<ffffffff8169cc3c>] ret_from_fork+0x7c/0xb0 > >>> | [ 1801.984608] [<ffffffff81097230>] ? > >>> kthread_create_on_node+0x160/0x160 > >>> | [ 1802.062825] ---[ end trace d77f2054de000fb7 ]--- > >>> | > >>> | This issue is related to the bug 54411: > >>> | https://bugzilla.kernel.org/show_bug.cgi?id=54411 > >>> > >>> Add is_removed to record if pci_destroy_dev is called already. > >>> > >>> During second calling, still have extra dev ref hold via > >>> device_schedule_call, so we are safe to check dev->is_removed. > >>> > >>> It fixs the problem In Gu's test. > >>> > >>> -v2: add partial changelog from Gu Zheng <guz.f...@cn.fujitsu.com> > >>> refresh after patch of moving device_del from Rafael. > >>> > >>> Signed-off-by: Yinghai Lu <ying...@kernel.org> > >>> --- > >>> drivers/pci/remove.c | 8 +++++--- > >>> include/linux/pci.h | 1 + > >>> 2 files changed, 6 insertions(+), 3 deletions(-) > >>> > >>> diff --git a/drivers/pci/remove.c b/drivers/pci/remove.c > >>> index f452148..b090cec 100644 > >>> --- a/drivers/pci/remove.c > >>> +++ b/drivers/pci/remove.c > >>> @@ -20,9 +20,11 @@ static void pci_stop_dev(struct pci_dev *dev) > >>> > >>> static void pci_destroy_dev(struct pci_dev *dev) > >>> { > >>> - device_del(&dev->dev); > >>> - > >>> - put_device(&dev->dev); > >>> + if (!dev->is_removed) { > >>> + device_del(&dev->dev); > >>> + dev->is_removed = 1; > >> > >> As Rafael pointed out, this looks like a race. What prevents two > >> concurrent calls to pci_destroy_dev() from seeing "dev->is_removed == > >> 0" and both calling device_del() on the same device? > > > > hope you are happy with this one: > > -v3: use atomic operations to prevent racing that Rafael and Bjorn concern. > > Signed-off-by: Yinghai Lu <ying...@kernel.org> > > --- > drivers/pci/probe.c | 2 ++ > drivers/pci/remove.c | 8 +++++--- > include/linux/pci.h | 1 + > 3 files changed, 8 insertions(+), 3 deletions(-) > > Index: linux-2.6/drivers/pci/remove.c > =================================================================== > --- linux-2.6.orig/drivers/pci/remove.c > +++ linux-2.6/drivers/pci/remove.c > @@ -20,9 +20,11 @@ static void pci_stop_dev(struct pci_dev > > static void pci_destroy_dev(struct pci_dev *dev) > { > - device_del(&dev->dev); > - > - put_device(&dev->dev); > + if (atomic_inc_and_test(&dev->removed_count)) { > + device_del(&dev->dev); > + put_device(&dev->dev); > + } else > + atomic_dec(&dev->removed_count); > }
So assume pci_destroy_dev() is called twice in parallel for the same dev by two different threads. Thread 1 does the atomic_inc_and_test() and finds that it is OK to do the device_del() and put_device() which causes the device object to be freed. Then thread 2 does the atomic_inc_and_test() on the already freed device object and crashes the kernel. I think we need to be much more clever here ... Rafael -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
