[PATCH 2/2] iommu/vt-d: Use rcu_lock in get_resv_regions

Lu Baolu
2022-09-27T05:37:42Z

Commit 5f64ce5411b46 ("iommu/vt-d: Duplicate iommu_resv_region objects
per device list") converted rcu_lock in get_resv_regions to
dmar_global_lock to allow sleeping in iommu_alloc_resv_region(). This
introduced possible recursive locking if get_resv_regions is called from
within a section where intel_iommu_init() already holds dmar_global_lock.

Especially after commit c919739ce4721 ("iommu/vt-d: Handle race between
registration and device probe"), below lockdep splats could always be
seen.

============================================
WARNING: possible recursive locking detected
6.0.0-rc4+ #325 Tainted: G I
--------------------------------------------
swapper/0/1 is trying to acquire lock:
ffffffffa8a18c90 (dmar_global_lock){++++}-{3:3}, at:
intel_iommu_get_resv_regions+0x25/0x270

but task is already holding lock:
ffffffffa8a18c90 (dmar_global_lock){++++}-{3:3}, at:
intel_iommu_init+0x36d/0x6ea

...

Call Trace:
<TASK>
dump_stack_lvl+0x48/0x5f
__lock_acquire.cold.73+0xad/0x2bb
lock_acquire+0xc2/0x2e0
? intel_iommu_get_resv_regions+0x25/0x270
? lock_is_held_type+0x9d/0x110
down_read+0x42/0x150
? intel_iommu_get_resv_regions+0x25/0x270
intel_iommu_get_resv_regions+0x25/0x270
iommu_create_device_direct_mappings.isra.28+0x8d/0x1c0
? iommu_get_dma_cookie+0x6d/0x90
bus_iommu_probe+0x19f/0x2e0
iommu_device_register+0xd4/0x130
intel_iommu_init+0x3e1/0x6ea
? iommu_setup+0x289/0x289
? rdinit_setup+0x34/0x34
pci_iommu_init+0x12/0x3a
do_one_initcall+0x65/0x320
? rdinit_setup+0x34/0x34
? rcu_read_lock_sched_held+0x5a/0x80
kernel_init_freeable+0x28a/0x2f3
? rest_init+0x1b0/0x1b0
kernel_init+0x1a/0x130
ret_from_fork+0x1f/0x30
</TASK>

This rolls back dmar_global_lock to rcu_lock to avoid the lockdep splat.

Fixes: c919739ce4721 ("iommu/vt-d: Handle race between registration and device probe")
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
---
drivers/iommu/intel/iommu.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
index d5965b4f8b60..b3cf0f991e29 100644
--- a/drivers/iommu/intel/iommu.c
+++ b/drivers/iommu/intel/iommu.c
@@ -4534,7 +4534,7 @@ static void intel_iommu_get_resv_regions(struct device *device,
struct device *i_dev;
int i;

- down_read(&dmar_global_lock);
+ rcu_read_lock();
for_each_rmrr_units(rmrr) {
for_each_active_dev_scope(rmrr->devices, rmrr->devices_cnt,
i, i_dev) {
@@ -4553,14 +4553,14 @@ static void intel_iommu_get_resv_regions(struct device *device,

resv = iommu_alloc_resv_region(rmrr->base_address,
length, prot, type,
- GFP_KERNEL);
+ GFP_ATOMIC);
if (!resv)
break;

list_add_tail(&resv->list, head);
}
}
- up_read(&dmar_global_lock);
+ rcu_read_unlock();

#ifdef CONFIG_INTEL_IOMMU_FLOPPY_WA
if (dev_is_pci(device)) {
--
2.34.1