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    Subject[PATCH] introduce a default off mode for kmemleak
    Hi,

    Kmemleak can be very useful in figuring out where a kernel leak is
    suspected, but I've run into issues it which makes it hard to enable
    by default - reports false positives, oom kills on low memory systems (512 MB).
    Although these can be addressed, there is still the memory footprint,
    and runtime overhead, so I think it might make sense to create mode
    where it is disabled by default, but can still be enabled on the command
    line via: kmemleak=on.

    thanks,

    -Jason

    Introduce a new DEBUG_KMEMLEAK_DEFAULT_OFF config parameter that allows
    kmemleak to be disabled by default, but enabled on the command line via:
    kmemleak=on. Although a reboot is required to turn it on, its still
    useful to not require a re-compile.

    Signed-off-by: Jason Baron <jbaron@redhat.com>
    ---
    lib/Kconfig.debug | 7 +++++++
    mm/kmemleak.c | 26 +++++++++++++++++++++++++-
    2 files changed, 32 insertions(+), 1 deletions(-)

    diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
    index e722e9d..95ab402 100644
    --- a/lib/Kconfig.debug
    +++ b/lib/Kconfig.debug
    @@ -400,6 +400,13 @@ config DEBUG_KMEMLEAK_TEST

    If unsure, say N.

    +config DEBUG_KMEMLEAK_DEFAULT_OFF
    + bool "Default kmemleak to off"
    + depends on DEBUG_KMEMLEAK
    + help
    + Say Y here to disable kmemleak by default. It can then be enabled
    + on the command line via kmemleak=on.
    +
    config DEBUG_PREEMPT
    bool "Debug preemptible kernel"
    depends on DEBUG_KERNEL && PREEMPT && TRACE_IRQFLAGS_SUPPORT
    diff --git a/mm/kmemleak.c b/mm/kmemleak.c
    index 2c0d032..1006267 100644
    --- a/mm/kmemleak.c
    +++ b/mm/kmemleak.c
    @@ -211,6 +211,11 @@ static signed long jiffies_scan_wait;
    static int kmemleak_stack_scan = 1;
    /* protects the memory scanning, parameters and debug/kmemleak file access */
    static DEFINE_MUTEX(scan_mutex);
    +#ifdef CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF
    +/* setting kmemleak=on, will set this var, skipping the disable */
    +static int kmemleak_skip_disable;
    +#endif
    +

    /*
    * Early object allocation/freeing logging. Kmemleak is initialized after the
    @@ -1600,10 +1605,22 @@ static int kmemleak_boot_config(char *str)
    {
    if (!str)
    return -EINVAL;
    +
    if (strcmp(str, "off") == 0)
    +#ifdef CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF
    + return -EINVAL;
    +#else
    kmemleak_disable();
    - else if (strcmp(str, "on") != 0)
    +#endif
    + else if (strcmp(str, "on") == 0)
    +#ifdef CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF
    + kmemleak_skip_disable = 1;
    +#else
    + return -EINVAL;
    +#endif
    + else
    return -EINVAL;
    +
    return 0;
    }
    early_param("kmemleak", kmemleak_boot_config);
    @@ -1616,6 +1633,13 @@ void __init kmemleak_init(void)
    int i;
    unsigned long flags;

    +#ifdef CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF
    + if (!kmemleak_skip_disable) {
    + kmemleak_disable();
    + return;
    + }
    +#endif
    +
    jiffies_min_age = msecs_to_jiffies(MSECS_MIN_AGE);
    jiffies_scan_wait = msecs_to_jiffies(SECS_SCAN_WAIT * 1000);

    --
    1.7.1


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