This is a note to let you know that I've just added the patch titled sched/isolation: Allow "isolcpus=" to skip unknown sub-parameters to the 5.6-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: sched-isolation-allow-isolcpus-to-skip-unknown-sub-p.patch and it can be found in the queue-5.6 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. commit 7552d9131edfdf6f2c1f890c36060266c08c6ff2 Author: Peter Xu <peterx@xxxxxxxxxx> Date: Fri Apr 3 18:35:17 2020 -0400 sched/isolation: Allow "isolcpus=" to skip unknown sub-parameters [ Upstream commit 3662daf023500dc084fa3b96f68a6f46179ddc73 ] 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@xxxxxxxxxxxxx> Signed-off-by: Peter Xu <peterx@xxxxxxxxxx> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Link: https://lkml.kernel.org/r/20200403223517.406353-1-peterx@xxxxxxxxxx Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c index 008d6ac2342b7..808244f3ddd98 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 */