On 2020-11-12 22:05, John Stultz wrote:
In trying to handle a possible driver probe ordering issue
brought up by Robin Murphy, I ran across a separate null pointer
crash in the iommu core in iommu_group_remove_device():
[ 2.732803] dwc3-qcom a6f8800.usb: failed to get usb-ddr path: -517
[ 2.739281] Unable to handle kernel NULL pointer dereference at virtual address 00000000000000c0
...
[ 2.775619] [00000000000000c0] user address but active_mm is swapper
[ 2.782039] Internal error: Oops: 96000005 [#1] PREEMPT SMP
[ 2.787670] Modules linked in:
[ 2.790769] CPU: 6 PID: 1 Comm: swapper/0 Tainted: G W 5.10.0-rc1-mainline-00025-g272a618fc36-dirty #3973
[ 2.801719] Hardware name: Thundercomm Dragonboard 845c (DT)
[ 2.807431] pstate: 00c00005 (nzcv daif +PAN +UAO -TCO BTYPE=--)
[ 2.813508] pc : iommu_group_remove_device+0x30/0x1b0
[ 2.818611] lr : iommu_release_device+0x4c/0x78
[ 2.823189] sp : ffffffc01005b950
...
[ 2.907082] Call trace:
[ 2.909566] iommu_group_remove_device+0x30/0x1b0
[ 2.914323] iommu_release_device+0x4c/0x78
[ 2.918559] iommu_bus_notifier+0xe8/0x108
[ 2.922708] blocking_notifier_call_chain+0x78/0xb8
[ 2.927641] device_del+0x2ac/0x3d0
[ 2.931177] platform_device_del.part.9+0x20/0x98
[ 2.935933] platform_device_unregister+0x2c/0x40
[ 2.940694] of_platform_device_destroy+0xd8/0xe0
[ 2.945450] device_for_each_child_reverse+0x58/0xb0
[ 2.950471] of_platform_depopulate+0x4c/0x78
[ 2.954886] dwc3_qcom_probe+0x93c/0xcb8
[ 2.958858] platform_drv_probe+0x58/0xa8
[ 2.962917] really_probe+0xec/0x398
[ 2.966531] driver_probe_device+0x5c/0xb8
[ 2.970677] device_driver_attach+0x74/0x98
[ 2.974911] __driver_attach+0x60/0xe8
[ 2.978700] bus_for_each_dev+0x84/0xd8
[ 2.982581] driver_attach+0x30/0x40
[ 2.986194] bus_add_driver+0x160/0x208
[ 2.990076] driver_register+0x64/0x110
[ 2.993957] __platform_driver_register+0x58/0x68
[ 2.998716] dwc3_qcom_driver_init+0x20/0x28
[ 3.003041] do_one_initcall+0x6c/0x2d0
[ 3.006925] kernel_init_freeable+0x214/0x268
[ 3.011339] kernel_init+0x18/0x118
[ 3.014876] ret_from_fork+0x10/0x18
[ 3.018495] Code: d0006a21 f9417295 91130021 910162b6 (b940c2a2)
In the case above, the arm-smmu driver fails to probe with
EPROBE_DEFER, and I'm guessing I'm guessing that causes
iommu_group_add_device() to fail and sets the
dev->iommu_group = NULL, then somehow we hit
iommu_group_remove_device() and trip over the null value?
I'm not really sure...
Anyway, adding the null check seems to avoid the issue and the
system boots fine after the arm-smmu driver later reprobed.
Feedback or better ideas for a solution would be appreciated!
I think the real issue is that we shouldn't even be here. If the device
was still waiting for an IOMMU when it got torn down, then dev->iommu
would be non-NULL due to a fwspec being allocated, but it's possible
that none of the other setup would have been done, so
iommu_release_device() shouldn't be blindly trying to undo it. It
happens that iommu_device_unlink() and arm_smmu_release_device() still
have some left-over tolerance for invalid inputs, but even if we do make
iommu_group_remove_device() similarly tolerant of invalid input, the
subsequent module_put() could still be unbalanced if the fwspec and
deferral came from of_iommu_configure() without iommu_probe_device()
even being called. Therefore I think this needs to be fundamentally
fixed by making iommu_release_device() better at handling
partially-configured devices in the first place.
Robin.
Cc: Robin Murphy <robin.murphy@xxxxxxx>
Cc: Will Deacon <will@xxxxxxxxxx>
Cc: Andy Gross <agross@xxxxxxxxxx>
Cc: Maulik Shah <mkshah@xxxxxxxxxxxxxx>
Cc: Bjorn Andersson <bjorn.andersson@xxxxxxxxxx>
Cc: Saravana Kannan <saravanak@xxxxxxxxxx>
Cc: Marc Zyngier <maz@xxxxxxxxxx>
Cc: Lina Iyer <ilina@xxxxxxxxxxxxxx>
Cc: iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx
Cc: linux-arm-msm <linux-arm-msm@xxxxxxxxxxxxxxx>
Signed-off-by: John Stultz <john.stultz@xxxxxxxxxx>
---
drivers/iommu/iommu.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index b53446bb8c6b4..28229f7ef7d5a 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -877,6 +877,10 @@ void iommu_group_remove_device(struct device *dev)
struct iommu_group *group = dev->iommu_group;
struct group_device *tmp_device, *device = NULL;
+ /* Avoid crash if iommu_group value is null */
+ if (!group)
+ return;
+
dev_info(dev, "Removing from iommu group %d\n", group->id);
/* Pre-notify listeners that a device is being removed. */
