[PATCH] kho: print which scratch buffer failed to be reserved

[PATCH] kho: print which scratch buffer failed to be reserved

[Pratyush Yadav]

From: "Pratyush Yadav (Google)" <pratyush@kernel.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@kernel.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

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

[Mike Rapoport]

On Fri, Jan 16, 2026 at 04:54:11PM +0000, Pratyush Yadav wrote:
> From: "Pratyush Yadav (Google)" <pratyush@kernel.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@kernel.org>

Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>

-- 
Sincerely yours,
Mike.

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

[Pasha Tatashin]

On Fri, Jan 16, 2026 at 11:54 AM Pratyush Yadav <pratyush@kernel.org> wrote:
>
> From: "Pratyush Yadav (Google)" <pratyush@kernel.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@kernel.org>

Reviewed-by: Pasha Tatashin <pasha.tatashin@soleen.com>

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

[Samiullah Khawaja]

On Fri, Jan 16, 2026 at 8:54 AM Pratyush Yadav <pratyush@kernel.org> wrote:
>
> From: "Pratyush Yadav (Google)" <pratyush@kernel.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@kernel.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@google.com>
Tested-by: Samiullah Khawaja <skhawaja@google.com>

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