Re: [PATCH 1/1] iommu/vt-d: Fix suspicious RCU usage

[Breno Leitao]

On Tue, Feb 18, 2025 at 12:14:53PM +0200, Ido Schimmel wrote:
> + Breno who also encountered this issue

Thanks. Please add the following if you feel appropriate.

Reported-by: Breno Leitao <leitao@xxxxxxxxxx>

> 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>

Tested-by: Breno Leitao <leitao@xxxxxxxxxx>