Re: [PATCH v3 01/30] kho: init new_physxa->phys_bits to fix lockdep

[Pratyush Yadav <pratyush@kernel.org>]

Hi Pasha,

On Thu, Aug 07 2025, Pasha Tatashin wrote:

> Lockdep shows the following warning:
>
> INFO: trying to register non-static key.
> The code is fine but needs lockdep annotation, or maybe
> you didn't initialize this object before use?
> turning off the locking correctness validator.
>
> [<ffffffff810133a6>] dump_stack_lvl+0x66/0xa0
> [<ffffffff8136012c>] assign_lock_key+0x10c/0x120
> [<ffffffff81358bb4>] register_lock_class+0xf4/0x2f0
> [<ffffffff813597ff>] __lock_acquire+0x7f/0x2c40
> [<ffffffff81360cb0>] ? __pfx_hlock_conflict+0x10/0x10
> [<ffffffff811707be>] ? native_flush_tlb_global+0x8e/0xa0
> [<ffffffff8117096e>] ? __flush_tlb_all+0x4e/0xa0
> [<ffffffff81172fc2>] ? __kernel_map_pages+0x112/0x140
> [<ffffffff813ec327>] ? xa_load_or_alloc+0x67/0xe0
> [<ffffffff81359556>] lock_acquire+0xe6/0x280
> [<ffffffff813ec327>] ? xa_load_or_alloc+0x67/0xe0
> [<ffffffff8100b9e0>] _raw_spin_lock+0x30/0x40
> [<ffffffff813ec327>] ? xa_load_or_alloc+0x67/0xe0
> [<ffffffff813ec327>] xa_load_or_alloc+0x67/0xe0
> [<ffffffff813eb4c0>] kho_preserve_folio+0x90/0x100
> [<ffffffff813ebb7f>] __kho_finalize+0xcf/0x400
> [<ffffffff813ebef4>] kho_finalize+0x34/0x70
>
> This is becase xa has its own lock, that is not initialized in
> xa_load_or_alloc.
>
> Modifiy __kho_preserve_order(), to properly call
> xa_init(&new_physxa->phys_bits);
>
> Fixes: fc33e4b44b27 ("kexec: enable KHO support for memory preservation")
> Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
> Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
> ---
>  kernel/kexec_handover.c | 29 +++++++++++++++++++++++++----
>  1 file changed, 25 insertions(+), 4 deletions(-)
>
> diff --git a/kernel/kexec_handover.c b/kernel/kexec_handover.c
> index e49743ae52c5..6240bc38305b 100644
> --- a/kernel/kexec_handover.c
> +++ b/kernel/kexec_handover.c
> @@ -144,14 +144,35 @@ static int __kho_preserve_order(struct kho_mem_track *track, unsigned long pfn,
>  				unsigned int order)
>  {
>  	struct kho_mem_phys_bits *bits;
> -	struct kho_mem_phys *physxa;
> +	struct kho_mem_phys *physxa, *new_physxa;
>  	const unsigned long pfn_high = pfn >> order;
>  
>  	might_sleep();
>  
> -	physxa = xa_load_or_alloc(&track->orders, order, sizeof(*physxa));
> -	if (IS_ERR(physxa))
> -		return PTR_ERR(physxa);
> +	physxa = xa_load(&track->orders, order);
> +	if (!physxa) {
> +		new_physxa = kzalloc(sizeof(*physxa), GFP_KERNEL);
> +		if (!new_physxa)
> +			return -ENOMEM;
> +
> +		xa_init(&new_physxa->phys_bits);
> +		physxa = xa_cmpxchg(&track->orders, order, NULL, new_physxa,
> +				    GFP_KERNEL);
> +		if (xa_is_err(physxa)) {
> +			int err = xa_err(physxa);
> +
> +			xa_destroy(&new_physxa->phys_bits);
> +			kfree(new_physxa);
> +
> +			return err;
> +		}
> +		if (physxa) {
> +			xa_destroy(&new_physxa->phys_bits);
> +			kfree(new_physxa);
> +		} else {
> +			physxa = new_physxa;
> +		}

I suppose this could be simplified a bit to:

	err = xa_err(physxa);
        if (err || physxa) {
        	xa_destroy(&new_physxa->phys_bits);
                kfree(new_physxa);

		if (err)
                	return err;
	} else {
        	physxa = new_physxa;
	}

No strong preference though, so fine either way. Up to you.

Reviewed-by: Pratyush Yadav <pratyush@kernel.org>

> +	}
>  
>  	bits = xa_load_or_alloc(&physxa->phys_bits, pfn_high / PRESERVE_BITS,
>  				sizeof(*bits));

-- 
Regards,
Pratyush Yadav