Re: [PATCH v5] USB host: Fix lockdep warning in AMD PLL quirk

From: Sergei Shtylyov
Date: Mon Apr 11 2011 - 06:01:59 EST


On 11-04-2011 10:59, Roedel, Joerg wrote:

You mean 2.6.39-rc2 right? I'm asking because I hit the same warning
with 39-rc2 now too but it didn't appear with .38 - so it has to have
snuck in after the merge window. If so, you don't need the stable tag.

You were right, just tested plain 2.6.38 and it doesn't happen. So I
removed the stable tag. Here is the updated patch.

From 6b9a9018cf0b847dcd906c269d663668e67a097d Mon Sep 17 00:00:00 2001
From: Joerg Roedel<joerg.roedel@xxxxxxx>
Date: Wed, 6 Apr 2011 13:07:53 +0200
Subject: [PATCH] USB host: Fix lockdep warning in AMD PLL quirk

Booting 2.6.38 on my test machine produces a lockdep warning

You've just said that this doesn't happen with plain 2.6.38...

from the usb_amd_find_chipset_info() function:

WARNING: at /data/lemmy/linux.trees.git/kernel/lockdep.c:2465 lockdep_trace_alloc+0x95/0xc2()
Hardware name: Snook
Modules linked in:
Pid: 959, comm: work_for_cpu Not tainted 2.6.39-rc2+ #22
Call Trace:
[<ffffffff8103c0d4>] warn_slowpath_common+0x80/0x98
[<ffffffff812387e6>] ? T.492+0x24/0x26
[<ffffffff8103c101>] warn_slowpath_null+0x15/0x17
[<ffffffff81068667>] lockdep_trace_alloc+0x95/0xc2
[<ffffffff810ed9ac>] slab_pre_alloc_hook+0x18/0x3b
[<ffffffff810ef227>] kmem_cache_alloc_trace+0x25/0xba
[<ffffffff812387e6>] T.492+0x24/0x26
[<ffffffff81238816>] pci_get_subsys+0x2e/0x73
[<ffffffff8123886c>] pci_get_device+0x11/0x13
[<ffffffff814082a9>] usb_amd_find_chipset_info+0x3f/0x18a

It turns out that this function calls pci_get_device under a spin_lock
with irqs disabled, but the pci_get_device function is only allowed in
preemptible context.

This patch fixes the warning by making all data-structure
modifications on temporal storage and commiting this back
into the visible structure at the end. While at it, this
patch also moves the pci_dev_put calls out of the spinlocks
because this function might sleep too.

Signed-off-by: Joerg Roedel <joerg.roedel@xxxxxxx>
drivers/usb/host/pci-quirks.c | 117 ++++++++++++++++++++++++++---------------
1 files changed, 74 insertions(+), 43 deletions(-)

diff --git a/drivers/usb/host/pci-quirks.c b/drivers/usb/host/pci-quirks.c
index 1d586d4..c6eb69c 100644
--- a/drivers/usb/host/pci-quirks.c
+++ b/drivers/usb/host/pci-quirks.c
@@ -294,20 +322,23 @@ void usb_amd_dev_put(void)

- if (amd_chipset.nb_dev) {
- pci_dev_put(amd_chipset.nb_dev);
- amd_chipset.nb_dev = NULL;
- }
- if (amd_chipset.smbus_dev) {
- pci_dev_put(amd_chipset.smbus_dev);
- amd_chipset.smbus_dev = NULL;
- }
+ /* save them to pci_dev_put outside of spinlock */
+ nb = amd_chipset.nb_dev;
+ smbus = amd_chipset.smbus_dev;
+ amd_chipset.nb_dev = NULL;
+ amd_chipset.smbus_dev = NULL;
amd_chipset.nb_type = 0;
amd_chipset.sb_type = 0;
amd_chipset.isoc_reqs = 0;
amd_chipset.probe_result = 0;

spin_unlock_irqrestore(&amd_lock, flags);
+ if (nb)
+ pci_dev_put(nb);
+ if (smbus)
+ pci_dev_put(amd_chipset.smbus_dev);

Haven't you just set this to NULL?

WBR, Sergei
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