[tip:x86/cache] x86/intel_rdt: Fix a silent failure when writing zero value schemata

[tip-bot for Xiaochen Shen <tipbot@zytor.com>]

Commit-ID:  2244645ab194fe45ffcbaa08f235c8f0c7fb54fc
Gitweb:     https://git.kernel.org/tip/2244645ab194fe45ffcbaa08f235c8f0c7fb54fc
Author:     Xiaochen Shen <xiaochen.shen@intel.com>
AuthorDate: Fri, 10 Nov 2017 11:16:24 -0800
Committer:  Thomas Gleixner <tglx@linutronix.de>
CommitDate: Sun, 12 Nov 2017 09:01:40 +0100

x86/intel_rdt: Fix a silent failure when writing zero value schemata

Writing an invalid schemata with no domain values (e.g., "(L3|MB):"),
results in a silent failure, i.e. the last_cmd_status returns OK,

Check for an empty value and set the result string with a proper error
message and return -EINVAL.

Before the fix:
 # mkdir /sys/fs/resctrl/p1

 # echo "L3:" > /sys/fs/resctrl/p1/schemata
 (silent failure)
 # cat /sys/fs/resctrl/info/last_cmd_status
 ok

 # echo "MB:" > /sys/fs/resctrl/p1/schemata
 (silent failure)
 # cat /sys/fs/resctrl/info/last_cmd_status
 ok

After the fix:
 # mkdir /sys/fs/resctrl/p1

 # echo "L3:" > /sys/fs/resctrl/p1/schemata
 -bash: echo: write error: Invalid argument
 # cat /sys/fs/resctrl/info/last_cmd_status
 Missing 'L3' value

 # echo "MB:" > /sys/fs/resctrl/p1/schemata
 -bash: echo: write error: Invalid argument
 # cat /sys/fs/resctrl/info/last_cmd_status
 Missing 'MB' value

[ Tony: This is an unintended side effect of the patch earlier to allow the
    	user to just write the value they want to change.  While allowing
    	user to specify less than all of the values, it also allows an
    	empty value. ]

Fixes: c4026b7b95a4 ("x86/intel_rdt: Implement "update" mode when writing schemata file")
Signed-off-by: Xiaochen Shen <xiaochen.shen@intel.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Vikas Shivappa <vikas.shivappa@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Link: https://lkml.kernel.org/r/20171110191624.20280-1-tony.luck@intel.com

---
 arch/x86/kernel/cpu/intel_rdt_ctrlmondata.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/x86/kernel/cpu/intel_rdt_ctrlmondata.c b/arch/x86/kernel/cpu/intel_rdt_ctrlmondata.c
index 30aeb26..23e1d5c 100644
--- a/arch/x86/kernel/cpu/intel_rdt_ctrlmondata.c
+++ b/arch/x86/kernel/cpu/intel_rdt_ctrlmondata.c
@@ -257,6 +257,11 @@ ssize_t rdtgroup_schemata_write(struct kernfs_open_file *of,
 			ret = -EINVAL;
 			goto out;
 		}
+		if (tok[0] == '\0') {
+			rdt_last_cmd_printf("Missing '%s' value\n", resname);
+			ret = -EINVAL;
+			goto out;
+		}
 		ret = rdtgroup_parse_resource(resname, tok, closid);
 		if (ret)
 			goto out;