On Thu 18-05-17 14:00:41, Miroslav Benes wrote:
> Add write-only force attribute to livepatch sysfs infrastructure. We can
> use it later to force couple of events during a live patching process.
> Be it a sending of a fake signal or forcing of the tasks' successful
> conversion.
>
> It does not make sense to use the force facility when there is no
> transaction running (although there is no harm doing that). Therefore we
> limit only to situations when klp_transition_patch variable is set.
> Normally, klp_mutex lock should be grabbed, because the variable is
> shared. However that would hold the action back unnecessarily because of
> waiting for the lock, so we omit the lock here. The resulting race
> window is harmless (using force when there is no transaction running).
>
> Signed-off-by: Miroslav Benes <mbenes@xxxxxxx>
> ---
> Documentation/ABI/testing/sysfs-kernel-livepatch | 9 +++++
> kernel/livepatch/core.c | 45 ++++++++++++++++++++++++
> 2 files changed, 54 insertions(+)
>
> diff --git a/Documentation/ABI/testing/sysfs-kernel-livepatch b/Documentation/ABI/testing/sysfs-kernel-livepatch
> index d5d39748382f..26e9f58cea9e 100644
> --- a/Documentation/ABI/testing/sysfs-kernel-livepatch
> +++ b/Documentation/ABI/testing/sysfs-kernel-livepatch
> @@ -8,6 +8,15 @@ Contact: live-patching@xxxxxxxxxxxxxxx
> The /sys/kernel/livepatch directory contains subdirectories for
> each loaded live patch module.
>
> +What: /sys/kernel/livepatch/force
> +Date: May 2017
> +KernelVersion: 4.13.0
> +Contact: live-patching@xxxxxxxxxxxxxxx
> +Description:
> + A write-only attribute that allows administrator to affect the
> + course of an existing transition. A fake signal can be send or
^^^^
"sent"
> + tasks TIF can be cleared.
> +
> What: /sys/kernel/livepatch/<patch>
> Date: Nov 2014
> KernelVersion: 3.19.0
> diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
> index b9628e43c78f..84f8944704ad 100644
> --- a/kernel/livepatch/core.c
> +++ b/kernel/livepatch/core.c
> @@ -437,6 +437,7 @@ EXPORT_SYMBOL_GPL(klp_enable_patch);
> * Sysfs Interface
> *
> * /sys/kernel/livepatch
> + * /sys/kernel/livepatch/force
> * /sys/kernel/livepatch/<patch>
> * /sys/kernel/livepatch/<patch>/enabled
> * /sys/kernel/livepatch/<patch>/transition
> @@ -444,6 +445,43 @@ EXPORT_SYMBOL_GPL(klp_enable_patch);
> * /sys/kernel/livepatch/<patch>/<object>/<function,sympos>
> */
>
> +static ssize_t force_store(struct kobject *kobj, struct kobj_attribute *attr,
> + const char *buf, size_t count)
> +{
> + unsigned long val;
> + int ret;
> +
> + ret = kstrtoul(buf, 10, &val);
> + if (ret)
> + return ret;
> +
> + /*
> + * klp_mutex lock is not grabbed here intentionally. It is not really
> + * needed. The race window is harmless and grabbing the lock would only
> + * hold the action back.
> + */
> + if (!klp_transition_patch) {
> + pr_info("no patching in progress. Force not allowed\n");
proposing smoother wording and information sharing
pr_info("no patching in progress, forced action (%d) ineffective", val);
> + return -EINVAL;
> + }
> +
> + switch (val) {
I felt strong confusion for a while looking at a function what does nothing. A
comment that this is intentionally an empty shell, at this stage, would be
welcome.
> + default:
> + return -EINVAL;
> + }
> +
> + return count;
> +}
> +
> +static struct kobj_attribute force_kobj_attr = __ATTR_WO(force);
> +static struct attribute *klp_attrs[] = {
> + &force_kobj_attr.attr,
> + NULL
> +};
> +static struct attribute_group klp_sysfs_group = {
> + .attrs = klp_attrs,
> +};
> +
> static ssize_t enabled_store(struct kobject *kobj, struct kobj_attribute *attr,
> const char *buf, size_t count)
> {
> @@ -954,6 +992,13 @@ static int __init klp_init(void)
> if (!klp_root_kobj)
> return -ENOMEM;
>
> + ret = sysfs_create_group(klp_root_kobj, &klp_sysfs_group);
> + if (ret) {
> + pr_err("cannot create livepatch attributes in sysfs\n");
> + kobject_put(klp_root_kobj);
> + return ret;
> + }
> +
> return 0;
> }
>
Libor
> --
> 2.12.2
>
> --
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--
Libor Pechacek
SUSE Labs
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