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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
This commit is contained in:
Peter Xu 2020-04-03 18:35:17 -04:00 committed by Thomas Gleixner
parent 8f3d9f3542
commit 3662daf023
1 changed files with 19 additions and 2 deletions
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21
kernel/sched/isolation.c
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@ -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 */