Messages in this thread Patch in this message | | | From | Peter Xu <> | Subject | [PATCH v3] sched/isolation: Allow "isolcpus=" to skip unknown sub-parameters | Date | Fri, 3 Apr 2020 18:35:17 -0400 |
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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
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