Commit <d74169ceb0d2> ("iommu/vt-d: Allocate DMAR fault interrupts
locally") moved the call to enable_drhd_fault_handling() to a code
path that does not hold any lock while traversing the drhd list. Fix
it by ensuring the dmar_global_lock lock is held when traversing the
drhd list.
Without this fix, the following warning is triggered:
=============================
WARNING: suspicious RCU usage
6.14.0-rc3 #55 Not tainted
-----------------------------
drivers/iommu/intel/dmar.c:2046 RCU-list traversed in non-reader section!!
other info that might help us debug this:
rcu_scheduler_active = 1, debug_locks = 1
2 locks held by cpuhp/1/23:
#0: ffffffff84a67c50 (cpu_hotplug_lock){++++}-{0:0}, at: cpuhp_thread_fun+0x87/0x2c0
#1: ffffffff84a6a380 (cpuhp_state-up){+.+.}-{0:0}, at: cpuhp_thread_fun+0x87/0x2c0
stack backtrace:
CPU: 1 UID: 0 PID: 23 Comm: cpuhp/1 Not tainted 6.14.0-rc3 #55
Call Trace:
<TASK>
dump_stack_lvl+0xb7/0xd0
lockdep_rcu_suspicious+0x159/0x1f0
? __pfx_enable_drhd_fault_handling+0x10/0x10
enable_drhd_fault_handling+0x151/0x180
cpuhp_invoke_callback+0x1df/0x990
cpuhp_thread_fun+0x1ea/0x2c0
smpboot_thread_fn+0x1f5/0x2e0
? __pfx_smpboot_thread_fn+0x10/0x10
kthread+0x12a/0x2d0
? __pfx_kthread+0x10/0x10
ret_from_fork+0x4a/0x60
? __pfx_kthread+0x10/0x10
ret_from_fork_asm+0x1a/0x30
</TASK>
Simply holding the lock in enable_drhd_fault_handling() will trigger a
lock order splat. Avoid holding the dmar_global_lock when calling
iommu_device_register(), which starts the device probe process.
Fixes: d74169ceb0d2 ("iommu/vt-d: Allocate DMAR fault interrupts locally")
Reported-by: Ido Schimmel <idosch@xxxxxxxxxx>
Closes: https://lore.kernel.org/linux-iommu/Zx9OwdLIc_VoQ0-a@xxxxxxxxxxxxxxxx/
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
---
drivers/iommu/intel/dmar.c | 1 +
drivers/iommu/intel/iommu.c | 7 +++++++
2 files changed, 8 insertions(+)
diff --git a/drivers/iommu/intel/dmar.c b/drivers/iommu/intel/dmar.c
index 9f424acf474e..e540092d664d 100644
--- a/drivers/iommu/intel/dmar.c
+++ b/drivers/iommu/intel/dmar.c
@@ -2043,6 +2043,7 @@ int enable_drhd_fault_handling(unsigned int cpu)
/*
* Enable fault control interrupt.
*/
+ guard(rwsem_read)(&dmar_global_lock);
for_each_iommu(iommu, drhd) {
u32 fault_status;
int ret;
diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
index cc46098f875b..9a1e61b429ca 100644
--- a/drivers/iommu/intel/iommu.c
+++ b/drivers/iommu/intel/iommu.c
@@ -3146,7 +3146,14 @@ int __init intel_iommu_init(void)
iommu_device_sysfs_add(&iommu->iommu, NULL,
intel_iommu_groups,
"%s", iommu->name);
+ /*
+ * The iommu device probe is protected by the iommu_probe_device_lock.
+ * Release the dmar_global_lock before entering the device probe path
+ * to avoid unnecessary lock order splat.
+ */
+ up_read(&dmar_global_lock);
iommu_device_register(&iommu->iommu, &intel_iommu_ops, NULL);
+ down_read(&dmar_global_lock);
iommu_pmu_register(iommu);
}
--
2.43.0
