[PATCH] kdump: Give crashkernel CMA areas unique names

[PATCH] kdump: Give crashkernel CMA areas unique names

[Mikhail Zaslonko]

reserve_crashkernel_cma() names every CMA area it reserves
"crashkernel". If the requested size can't be reserved in one piece,
it falls back to several smaller areas, all with the same name.
With CONFIG_CMA_SYSFS, cma_sysfs_init() then fails to create the second
directory:

  sysfs: cannot create duplicate filename '/kernel/mm/cma/crashkernel'

and the error path removes the sysfs entries of all CMA areas.

With CONFIG_CMA_DEBUGFS, debugfs refuses the duplicate directories as
well:

  debugfs: 'crashkernel' already exists in 'cma'

so only the first area shows up in debugfs.

Keep the name of the first area and add the index to the others:
crashkernel, crashkernel1, crashkernel2, ...

Fixes: ab475510e042 ("kdump: implement reserve_crashkernel_cma")
Signed-off-by: Mikhail Zaslonko <zaslonko@linux.ibm.com>
---
Found while adding crashkernel CMA support for s390.

 kernel/crash_reserve.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/kernel/crash_reserve.c b/kernel/crash_reserve.c
index eee37a11380c..e58318b1e092 100644
--- a/kernel/crash_reserve.c
+++ b/kernel/crash_reserve.c
@@ -483,10 +483,16 @@ void __init reserve_crashkernel_cma(unsigned long long cma_size)
 	while (cma_size > reserved_size &&
 	       crashk_cma_cnt < CRASHKERNEL_CMA_RANGES_MAX) {
 
+		char name[CMA_MAX_NAME];
 		struct cma *res;
 
+		/* CMA area names show up in sysfs and debugfs, keep them unique */
+		if (crashk_cma_cnt)
+			snprintf(name, sizeof(name), "crashkernel%d", crashk_cma_cnt);
+		else
+			strscpy(name, "crashkernel");
 		if (cma_declare_contiguous(0, request_size, 0, 0, 0, false,
-				       "crashkernel", &res)) {
+				       name, &res)) {
 			/* reservation failed, try half-sized blocks */
 			if (request_size <= PAGE_SIZE)
 				break;

base-commit: f66469d9905b39d2c260a15d7d6db450f4db67c1
-- 
2.55.0

Re: [PATCH] kdump: Give crashkernel CMA areas unique names

[David Hildenbrand (Arm)]

On 11/6/26 11:43, Mikhail Zaslonko wrote:
> reserve_crashkernel_cma() names every CMA area it reserves
> "crashkernel". If the requested size can't be reserved in one piece,
> it falls back to several smaller areas, all with the same name.
> With CONFIG_CMA_SYSFS, cma_sysfs_init() then fails to create the second
> directory:
> 
>   sysfs: cannot create duplicate filename '/kernel/mm/cma/crashkernel'
> 
> and the error path removes the sysfs entries of all CMA areas.
> 
> With CONFIG_CMA_DEBUGFS, debugfs refuses the duplicate directories as
> well:
> 
>   debugfs: 'crashkernel' already exists in 'cma'
> 
> so only the first area shows up in debugfs.
> 
> Keep the name of the first area and add the index to the others:
> crashkernel, crashkernel1, crashkernel2, ...
> 
> Fixes: ab475510e042 ("kdump: implement reserve_crashkernel_cma")
> Signed-off-by: Mikhail Zaslonko <zaslonko@linux.ibm.com>
> ---

Acked-by: David Hildenbrand (Arm) <david@kernel.org>

-- 
Cheers,

David

Re: [PATCH] kdump: Give crashkernel CMA areas unique names

[Usama Arif]

On Fri,  6 Nov 2026 11:43:09 +0100 Mikhail Zaslonko <zaslonko@linux.ibm.com> wrote:

> reserve_crashkernel_cma() names every CMA area it reserves
> "crashkernel". If the requested size can't be reserved in one piece,
> it falls back to several smaller areas, all with the same name.
> With CONFIG_CMA_SYSFS, cma_sysfs_init() then fails to create the second
> directory:
> 
>   sysfs: cannot create duplicate filename '/kernel/mm/cma/crashkernel'
> 
> and the error path removes the sysfs entries of all CMA areas.
> 
> With CONFIG_CMA_DEBUGFS, debugfs refuses the duplicate directories as
> well:
> 
>   debugfs: 'crashkernel' already exists in 'cma'
> 
> so only the first area shows up in debugfs.
> 
> Keep the name of the first area and add the index to the others:
> crashkernel, crashkernel1, crashkernel2, ...
> 
> Fixes: ab475510e042 ("kdump: implement reserve_crashkernel_cma")
> Signed-off-by: Mikhail Zaslonko <zaslonko@linux.ibm.com>
> ---
> Found while adding crashkernel CMA support for s390.
> 
>  kernel/crash_reserve.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)

Thanks for the fix and pointing me to it in [1]!

Acked-by: Usama Arif <usama.arif@linux.dev>

[1] https://lore.kernel.org/all/20261106104309.3669583-1-zaslonko@linux.ibm.com/

> 
> diff --git a/kernel/crash_reserve.c b/kernel/crash_reserve.c
> index eee37a11380c..e58318b1e092 100644
> --- a/kernel/crash_reserve.c
> +++ b/kernel/crash_reserve.c
> @@ -483,10 +483,16 @@ void __init reserve_crashkernel_cma(unsigned long long cma_size)
>  	while (cma_size > reserved_size &&
>  	       crashk_cma_cnt < CRASHKERNEL_CMA_RANGES_MAX) {
>  
> +		char name[CMA_MAX_NAME];
>  		struct cma *res;
>  
> +		/* CMA area names show up in sysfs and debugfs, keep them unique */
> +		if (crashk_cma_cnt)
> +			snprintf(name, sizeof(name), "crashkernel%d", crashk_cma_cnt);
> +		else
> +			strscpy(name, "crashkernel");
>  		if (cma_declare_contiguous(0, request_size, 0, 0, 0, false,
> -				       "crashkernel", &res)) {
> +				       name, &res)) {
>  			/* reservation failed, try half-sized blocks */
>  			if (request_size <= PAGE_SIZE)
>  				break;
> 
> base-commit: f66469d9905b39d2c260a15d7d6db450f4db67c1
> -- 
> 2.55.0
> 
> 

Re: [PATCH] kdump: Give crashkernel CMA areas unique names

[Jiri Bohac]

On Fri, Nov 06, 2026 at 11:43:09AM +0100, Mikhail Zaslonko wrote:
> reserve_crashkernel_cma() names every CMA area it reserves
> "crashkernel". If the requested size can't be reserved in one piece,
> it falls back to several smaller areas, all with the same name.
> With CONFIG_CMA_SYSFS, cma_sysfs_init() then fails to create the second
> directory:
> 
>   sysfs: cannot create duplicate filename '/kernel/mm/cma/crashkernel'
> 
> and the error path removes the sysfs entries of all CMA areas.
> 
> With CONFIG_CMA_DEBUGFS, debugfs refuses the duplicate directories as
> well:
> 
>   debugfs: 'crashkernel' already exists in 'cma'
> 
> so only the first area shows up in debugfs.
> 
> Keep the name of the first area and add the index to the others:
> crashkernel, crashkernel1, crashkernel2, ...
> 
> Fixes: ab475510e042 ("kdump: implement reserve_crashkernel_cma")
> Signed-off-by: Mikhail Zaslonko <zaslonko@linux.ibm.com>

Thanks for fixing this.

I don't think we really need the special case for crashk_cma_cnt == 0 
and that "crashkernel0" would be fine. But I don't mind either way.

Acked-by: Jiri Bohac <jbohac@suse.cz>

-- 
Jiri Bohac <jbohac@suse.cz>
SUSE Labs, Prague, Czechia