Re: [PATCH] powerpc/eeh_cache: Fix a possible debugfs deadlock

[Oliver O'Halloran]

On Thu, Oct 29, 2020 at 2:27 AM Qian Cai <cai@xxxxxxxxxx> wrote:
>
> Lockdep complains that a possible deadlock below in
> eeh_addr_cache_show() because it is acquiring a lock with IRQ enabled,
> but eeh_addr_cache_insert_dev() needs to acquire the same lock with IRQ
> disabled. Let's just make eeh_addr_cache_show() acquire the lock with
> IRQ disabled as well.
>
>         CPU0                    CPU1
>         ----                    ----
>    lock(&pci_io_addr_cache_root.piar_lock);
>                                 local_irq_disable();
>                                 lock(&tp->lock);
>                                 lock(&pci_io_addr_cache_root.piar_lock);
>    <Interrupt>
>      lock(&tp->lock);
>
>   *** DEADLOCK ***
>
>   lock_acquire+0x140/0x5f0
>   _raw_spin_lock_irqsave+0x64/0xb0
>   eeh_addr_cache_insert_dev+0x48/0x390
>   eeh_probe_device+0xb8/0x1a0
>   pnv_pcibios_bus_add_device+0x3c/0x80
>   pcibios_bus_add_device+0x118/0x290
>   pci_bus_add_device+0x28/0xe0
>   pci_bus_add_devices+0x54/0xb0
>   pcibios_init+0xc4/0x124
>   do_one_initcall+0xac/0x528
>   kernel_init_freeable+0x35c/0x3fc
>   kernel_init+0x24/0x148
>   ret_from_kernel_thread+0x5c/0x80
>
>   lock_acquire+0x140/0x5f0
>   _raw_spin_lock+0x4c/0x70
>   eeh_addr_cache_show+0x38/0x110
>   seq_read+0x1a0/0x660
>   vfs_read+0xc8/0x1f0
>   ksys_read+0x74/0x130
>   system_call_exception+0xf8/0x1d0
>   system_call_common+0xe8/0x218
>
> Fixes: 5ca85ae6318d ("powerpc/eeh_cache: Add a way to dump the EEH address cache")
> Signed-off-by: Qian Cai <cai@xxxxxxxxxx>

Good catch,

Reviewed-by: Oliver O'Halloran <oohall@xxxxxxxxx>