linux-kernel - Re: [PATCH] kho: print which scratch buffer failed to be reserved

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Message-ID: <CAAywjhTfAU-NH7+Wevp_UxquuJdUNuKvnv_Hzh6GDcFFxC1Bpg@mail.gmail.com>
Date: Thu, 22 Jan 2026 11:48:44 -0800
From: Samiullah Khawaja <skhawaja@...gle.com>
To: Pratyush Yadav <pratyush@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>, Alexander Graf <graf@...zon.com>, 
	Mike Rapoport <rppt@...nel.org>, Pasha Tatashin <pasha.tatashin@...een.com>, kexec@...ts.infradead.org, 
	linux-mm@...ck.org, linux-kernel@...r.kernel.org, 
	David Matlack <dmatlack@...gle.com>, Jason Miu <jasonmiu@...gle.com>
Subject: Re: [PATCH] kho: print which scratch buffer failed to be reserved

On Fri, Jan 16, 2026 at 8:54 AM Pratyush Yadav <pratyush@...nel.org> wrote:
>
> From: "Pratyush Yadav (Google)" <pratyush@...nel.org>
>
> When scratch area fails to reserve, KHO prints a message indicating
> that. But it doesn't say which scratch failed to allocate. This can be
> useful information for debugging. Even more so when the failure is hard
> to reproduce.
>
> Along with the current message, also print which exact scratch area
> failed to be reserved.
>
> Signed-off-by: Pratyush Yadav (Google) <pratyush@...nel.org>
> ---
>  kernel/liveupdate/kexec_handover.c | 16 ++++++++++++----
>  1 file changed, 12 insertions(+), 4 deletions(-)
>
> diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c
> index 49bf2cecab12..636bd96780ae 100644
> --- a/kernel/liveupdate/kexec_handover.c
> +++ b/kernel/liveupdate/kexec_handover.c
> @@ -651,8 +651,10 @@ static void __init kho_reserve_scratch(void)
>         kho_scratch_cnt = num_online_nodes() + 2;
>         size = kho_scratch_cnt * sizeof(*kho_scratch);
>         kho_scratch = memblock_alloc(size, PAGE_SIZE);
> -       if (!kho_scratch)
> +       if (!kho_scratch) {
> +               pr_err("Failed to reserve scratch array\n");
>                 goto err_disable_kho;
> +       }
>
>         /*
>          * reserve scratch area in low memory for lowmem allocations in the
> @@ -661,8 +663,10 @@ static void __init kho_reserve_scratch(void)
>         size = scratch_size_lowmem;
>         addr = memblock_phys_alloc_range(size, CMA_MIN_ALIGNMENT_BYTES, 0,
>                                          ARCH_LOW_ADDRESS_LIMIT);
> -       if (!addr)
> +       if (!addr) {
> +               pr_err("Failed to reserve lowmem scratch buffer\n");
>                 goto err_free_scratch_desc;
> +       }
>
>         kho_scratch[i].addr = addr;
>         kho_scratch[i].size = size;
> @@ -671,8 +675,10 @@ static void __init kho_reserve_scratch(void)
>         /* reserve large contiguous area for allocations without nid */
>         size = scratch_size_global;
>         addr = memblock_phys_alloc(size, CMA_MIN_ALIGNMENT_BYTES);
> -       if (!addr)
> +       if (!addr) {
> +               pr_err("Failed to reserve global scratch buffer\n");
>                 goto err_free_scratch_areas;
> +       }
>
>         kho_scratch[i].addr = addr;
>         kho_scratch[i].size = size;
> @@ -683,8 +689,10 @@ static void __init kho_reserve_scratch(void)
>                 addr = memblock_alloc_range_nid(size, CMA_MIN_ALIGNMENT_BYTES,
>                                                 0, MEMBLOCK_ALLOC_ACCESSIBLE,
>                                                 nid, true);
> -               if (!addr)
> +               if (!addr) {
> +                       pr_err("Failed to reserve nid %d scratch buffer\n", nid);
>                         goto err_free_scratch_areas;
> +               }
>
>                 kho_scratch[i].addr = addr;
>                 kho_scratch[i].size = size;
>
> base-commit: c37fac0551448c68e36f14782acaf662c7a1775e
> --
> 2.52.0.457.g6b5491de43-goog
>

Reviewed-by: Samiullah Khawaja <skhawaja@...gle.com>
Tested-by: Samiullah Khawaja <skhawaja@...gle.com>

Tested on my test machine while investigating the scratch space
allocation failure.