+ Breno who also encountered this issue
On Tue, Feb 18, 2025 at 10:24:21AM +0800, Lu Baolu wrote:
> 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>
Thanks for the fix. I tested it and the warning is gone.
Tested-by: Ido Schimmel <idosch@xxxxxxxxxx>
