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Date: Wed, 27 Nov 2013 02:24:20 +0100
From: "Rafael J. Wysocki" <rjw@...ysocki.net>
To: Yinghai Lu <yinghai@...nel.org>
Cc: Bjorn Helgaas <bhelgaas@...gle.com>,
"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
Gu Zheng <guz.fnst@...fujitsu.com>,
Guo Chao <yan@...ux.vnet.ibm.com>,
"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 04/10] PCI: Destroy pci dev only once
On Tuesday, November 26, 2013 12:13:50 PM Yinghai Lu wrote:
> On Tue, Nov 26, 2013 at 11:34 AM, Yinghai Lu <yinghai@...nel.org> wrote:
> > On Mon, Nov 25, 2013 at 7:38 PM, Bjorn Helgaas <bhelgaas@...gle.com> wrote:
> >> On Mon, Nov 25, 2013 at 6:28 PM, Yinghai Lu <yinghai@...nel.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.fnst@...fujitsu.com>
> >>> refresh after patch of moving device_del from Rafael.
> >>>
> >>> Signed-off-by: Yinghai Lu <yinghai@...nel.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 <yinghai@...nel.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
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