The last_cmd_status file is intended to report details about the most
recent resctrl filesystem operation, specifically to aid in diagnosing
failures.

However, when parsing io_alloc_cbm, if a user provides a domain ID that
does not exist in the resource, the operation fails with -EINVAL without
updating last_cmd_status. This results in inconsistent behaviour where
the system call returns an error, but last_cmd_status misleadingly reports
"ok", leaving the user unaware that the failure was caused by an invalid
domain ID.

Write an error message to last_cmd_status when the target domain ID cannot
be found.

Fixes: 28fa2cce7a83 ("fs/resctrl: Introduce interface to modify io_alloc capacity bitmasks")
Suggested-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: Aaron Tomlin <atomlin@atomlin.com>
---
 fs/resctrl/ctrlmondata.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/resctrl/ctrlmondata.c b/fs/resctrl/ctrlmondata.c
index cc4237c57cbe..2ef53161ce11 100644
--- a/fs/resctrl/ctrlmondata.c
+++ b/fs/resctrl/ctrlmondata.c
@@ -992,6 +992,7 @@ static int resctrl_io_alloc_parse_line(char *line,  struct rdt_resource *r,
 		}
 	}
 
+	rdt_last_cmd_printf("Invalid domain %lu\n", dom_id);
 	return -EINVAL;
 }
 
-- 
2.51.0

Hi Aaron,

On 3/24/26 5:11 PM, Aaron Tomlin wrote:
> The last_cmd_status file is intended to report details about the most
> recent resctrl filesystem operation, specifically to aid in diagnosing
> failures.
> 
> However, when parsing io_alloc_cbm, if a user provides a domain ID that
> does not exist in the resource, the operation fails with -EINVAL without
> updating last_cmd_status. This results in inconsistent behaviour where
> the system call returns an error, but last_cmd_status misleadingly reports
> "ok", leaving the user unaware that the failure was caused by an invalid
> domain ID.
> 
> Write an error message to last_cmd_status when the target domain ID cannot
> be found.
> 
> Fixes: 28fa2cce7a83 ("fs/resctrl: Introduce interface to modify io_alloc capacity bitmasks")
> Suggested-by: Reinette Chatre <reinette.chatre@intel.com>
> Signed-off-by: Aaron Tomlin <atomlin@atomlin.com>
> ---

Thank you.

Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>

Reinette

The following commit has been merged into the x86/cache branch of tip:

Commit-ID:     d06b8e7c97c3290e61006e30b32beb9e715fab82
Gitweb:        https://git.kernel.org/tip/d06b8e7c97c3290e61006e30b32beb9e715fab82
Author:        Aaron Tomlin <atomlin@atomlin.com>
AuthorDate:    Tue, 24 Mar 2026 20:11:58 -04:00
Committer:     Borislav Petkov (AMD) <bp@alien8.de>
CommitterDate: Thu, 02 Apr 2026 00:11:35 +02:00

fs/resctrl: Report invalid domain ID when parsing io_alloc_cbm

The last_cmd_status file is intended to report details about the most recent
resctrl filesystem operation, specifically to aid in diagnosing failures.

However, when parsing io_alloc_cbm, if a user provides a domain ID that does
not exist in the resource, the operation fails with -EINVAL without updating
last_cmd_status. This results in inconsistent behaviour where the system call
returns an error, but last_cmd_status misleadingly reports "ok", leaving the
user unaware that the failure was caused by an invalid domain ID.

Write an error message to last_cmd_status when the target domain ID cannot
be found.

Fixes: 28fa2cce7a83 ("fs/resctrl: Introduce interface to modify io_alloc capacity bitmasks")
Suggested-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: Aaron Tomlin <atomlin@atomlin.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
Reviewed-by: Babu Moger <babu.moger@amd.com>
Tested-by: Babu Moger <babu.moger@amd.com>
Link: https://patch.msgid.link/20260325001159.447075-2-atomlin@atomlin.com
---
 fs/resctrl/ctrlmondata.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/resctrl/ctrlmondata.c b/fs/resctrl/ctrlmondata.c
index cc4237c..2ef5316 100644
--- a/fs/resctrl/ctrlmondata.c
+++ b/fs/resctrl/ctrlmondata.c
@@ -992,6 +992,7 @@ next:
 		}
 	}
 
+	rdt_last_cmd_printf("Invalid domain %lu\n", dom_id);
 	return -EINVAL;
 }