[PATCH v3] sched/isolation: Allow "isolcpus=" to skip unknown sub-parameters

[PATCH v3] sched/isolation: Allow "isolcpus=" to skip unknown sub-parameters

[Peter Xu]

The "isolcpus=" parameter allows sub-parameters to exist before the
cpulist is specified, and if it sees unknown sub-parameters the whole
parameter will be ignored.  This design is incompatible with itself
when we add more sub-parameters to "isolcpus=", because the old
kernels will not recognize the new "isolcpus=" sub-parameters, then it
will invalidate the whole parameter so the CPU isolation will not
really take effect if we start to use the new sub-parameters while
later we reboot into an old kernel. Instead we will see this when
booting the old kernel:

    isolcpus: Error, unknown flag

The better and compatible way is to allow "isolcpus=" to skip unknown
sub-parameters, so that even if we add new sub-parameters to it the
old kernel will still be able to behave as usual even if with the new
sub-parameter is specified.

Ideally this patch should be there when we introduce the first
sub-parameter for "isolcpus=", so it's already a bit late.  However
late is better than nothing.

CC: Ming Lei <ming.lei@redhat.com>
CC: Ingo Molnar <mingo@redhat.com>
CC: Peter Zijlstra <peterz@infradead.org>
CC: Juri Lelli <juri.lelli@redhat.com>
CC: Luiz Capitulino <lcapitulino@redhat.com>
Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Xu <peterx@redhat.com>
---
v3:
- add brackets for for loop
- move "illegal" a bit higher, which may look tiny bit nicer
- also allow '_'
v2:
- only allow isalpha() for sub-parameters [tglx]
---
 kernel/sched/isolation.c | 21 +++++++++++++++++++--
 1 file changed, 19 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c
index 008d6ac2342b..808244f3ddd9 100644
--- 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 */
-- 
2.24.1

Re: [PATCH v3] sched/isolation: Allow "isolcpus=" to skip unknown sub-parameters

[Peter Xu]

Ping - Thomas, do you think this version is ok to you?

This has missed 5.7 already, am I right?

Thanks,

On Fri, Apr 03, 2020 at 06:35:17PM -0400, Peter Xu wrote:
> The "isolcpus=" parameter allows sub-parameters to exist before the
> cpulist is specified, and if it sees unknown sub-parameters the whole
> parameter will be ignored.  This design is incompatible with itself
> when we add more sub-parameters to "isolcpus=", because the old
> kernels will not recognize the new "isolcpus=" sub-parameters, then it
> will invalidate the whole parameter so the CPU isolation will not
> really take effect if we start to use the new sub-parameters while
> later we reboot into an old kernel. Instead we will see this when
> booting the old kernel:
> 
>     isolcpus: Error, unknown flag
> 
> The better and compatible way is to allow "isolcpus=" to skip unknown
> sub-parameters, so that even if we add new sub-parameters to it the
> old kernel will still be able to behave as usual even if with the new
> sub-parameter is specified.
> 
> Ideally this patch should be there when we introduce the first
> sub-parameter for "isolcpus=", so it's already a bit late.  However
> late is better than nothing.
> 
> CC: Ming Lei <ming.lei@redhat.com>
> CC: Ingo Molnar <mingo@redhat.com>
> CC: Peter Zijlstra <peterz@infradead.org>
> CC: Juri Lelli <juri.lelli@redhat.com>
> CC: Luiz Capitulino <lcapitulino@redhat.com>
> Suggested-by: Thomas Gleixner <tglx@linutronix.de>
> Signed-off-by: Peter Xu <peterx@redhat.com>
> ---
> v3:
> - add brackets for for loop
> - move "illegal" a bit higher, which may look tiny bit nicer
> - also allow '_'
> v2:
> - only allow isalpha() for sub-parameters [tglx]
> ---
>  kernel/sched/isolation.c | 21 +++++++++++++++++++--
>  1 file changed, 19 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c
> index 008d6ac2342b..808244f3ddd9 100644
> --- 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 */
> -- 
> 2.24.1
> 

-- 
Peter Xu

[tip: sched/core] sched/isolation: Allow "isolcpus=" to skip unknown sub-parameters

[tip-bot2 for Peter Xu]

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     3662daf023500dc084fa3b96f68a6f46179ddc73
Gitweb:        https://git.kernel.org/tip/3662daf023500dc084fa3b96f68a6f46179ddc73
Author:        Peter Xu <peterx@redhat.com>
AuthorDate:    Fri, 03 Apr 2020 18:35:17 -04:00
Committer:     Thomas Gleixner <tglx@linutronix.de>
CommitterDate: Wed, 15 Apr 2020 10:38:26 +02:00

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

---
 kernel/sched/isolation.c | 21 +++++++++++++++++++--
 1 file changed, 19 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c
index 008d6ac..808244f 100644
--- 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 */