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    Subject[PATCH 5.6 086/106] sched/isolation: Allow "isolcpus=" to skip unknown sub-parameters
    Date
    From: Peter Xu <peterx@redhat.com>

    [ 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@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
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    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 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 */
    --
    2.20.1


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