sched/isolation: Allow "isolcpus=" to skip unknown sub-parameters

The "isolcpus=" parameter allows sub-parameters before the cpulist is
specified, and if the parser detects an unknown sub-parameters the whole
parameter will be ignored.

This design is incompatible with itself when new sub-parameters are added.
An older kernel will not recognize the new sub-parameter and will
invalidate the whole parameter so the CPU isolation will not take
effect. It emits a warning:

    isolcpus: Error, unknown flag

The better and compatible way is to allow "isolcpus=" to skip unknown
sub-parameters, so that even if new sub-parameters are added an older
kernel will still be able to behave as usual even if with the new
sub-parameter specified on the command line.

Ideally this should have been there when the first sub-parameter for
"isolcpus=" was introduced.

Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20200403223517.406353-1-peterx@redhat.com

diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c
index 008d6ac2342b7536fff293b2ce7054cf9d9cfc98..808244f3ddd9842d684503a493cd8a69092cff74 100644 (file)
--- a/kernel/sched/isolation.c
+++ b/kernel/sched/isolation.c
@@ -149,6 +149,9 @@ __setup("nohz_full=", housekeeping_nohz_full_setup);
 static int __init housekeeping_isolcpus_setup(char *str)
 {
        unsigned int flags = 0;
+       bool illegal = false;
+       char *par;
+       int len;
 
        while (isalpha(*str)) {
                if (!strncmp(str, "nohz,", 5)) {
@@ -169,8 +172,22 @@ static int __init housekeeping_isolcpus_setup(char *str)
                        continue;
                }
 
-               pr_warn("isolcpus: Error, unknown flag\n");
-               return 0;
+               /*
+                * Skip unknown sub-parameter and validate that it is not
+                * containing an invalid character.
+                */
+               for (par = str, len = 0; *str && *str != ','; str++, len++) {
+                       if (!isalpha(*str) && *str != '_')
+                               illegal = true;
+               }
+
+               if (illegal) {
+                       pr_warn("isolcpus: Invalid flag %.*s\n", len, par);
+                       return 0;
+               }
+
+               pr_info("isolcpus: Skipped unknown flag %.*s\n", len, par);
+               str++;
        }
 
        /* Default behaviour for isolcpus without flags */