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bus: fsl_mc: Fix driver_managed_dma check

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Since it's not currently safe to take device_lock() in the IOMMU probe
path, that can race against really_probe() setting dev->driver before
attempting to bind. The race itself isn't so bad, since we're only
concerned with dereferencing dev->driver itself anyway, but sadly my
attempt to implement the check with minimal churn leads to a kind of
TOCTOU issue, where dev->driver becomes valid after to_fsl_mc_driver(NULL)
is already computed, and thus the check fails to work as intended.

Will and I both hit this with the platform bus, but the pattern here is
the same, so fix it for correctness too.

Reported-by: Will McVicker <willmcvicker@google.com>
Fixes: bcb81ac6ae ("iommu: Get DT/ACPI parsing into the proper probe path")
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Reviewed-by: Will McVicker <willmcvicker@google.com>
Link: https://lore.kernel.org/r/20250425133929.646493-3-robin.murphy@arm.com
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
This commit is contained in:
Robin Murphy 2025-04-25 14:39:28 +01:00 committed by Christophe Leroy
parent 23d0601368
commit 152f33ee30
1 changed files with 3 additions and 3 deletions
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6
drivers/bus/fsl-mc/fsl-mc-bus.c
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@ -139,9 +139,9 @@ static int fsl_mc_bus_uevent(const struct device *dev, struct kobj_uevent_env *e
static int fsl_mc_dma_configure(struct device *dev)
{
const struct device_driver *drv = READ_ONCE(dev->driver);
struct device *dma_dev = dev;
struct fsl_mc_device *mc_dev = to_fsl_mc_device(dev);
struct fsl_mc_driver *mc_drv = to_fsl_mc_driver(dev->driver);
u32 input_id = mc_dev->icid;
int ret;
@ -153,8 +153,8 @@ static int fsl_mc_dma_configure(struct device *dev)
else
ret = acpi_dma_configure_id(dev, DEV_DMA_COHERENT, &input_id);
/* @mc_drv may not be valid when we're called from the IOMMU layer */
if (!ret && dev->driver && !mc_drv->driver_managed_dma) {
/* @drv may not be valid when we're called from the IOMMU layer */
if (!ret && drv && !to_fsl_mc_driver(drv)->driver_managed_dma) {
ret = iommu_device_use_default_domain(dev);
if (ret)
arch_teardown_dma_ops(dev);