On Fri, Mar 24, 2023 at 09:54:48AM +0100, Vlastimil Babka wrote:
> On 3/24/23 01:18, Masami Hiramatsu (Google) wrote:
> > Hi Beau,
> >
> > On Tue, 21 Feb 2023 13:11:43 -0800
> > Beau Belgrave <beaub@xxxxxxxxxxxxxxxxxxx> wrote:
> >
> >> Operators want to be able to ensure enough tracepoints exist on the
> >> system for kernel components as well as for user components. Since there
> >> are only up to 64K events, by default allow up to half to be used by
> >> user events.
> >>
> >> Add a boot parameter (user_events_max=%d) and a kernel sysctl parameter
> >> (kernel.user_events_max) to set a global limit that is honored among all
> >> groups on the system. This ensures hard limits can be setup to prevent
> >> user processes from consuming all event IDs on the system.
> >
> > sysctl is good to me, but would we really need the kernel parameter?
> > The user_events starts using when user-space is up, so I think setting
> > the limit with sysctl is enough.
> >
> > BTW, Vlastimil tried to add 'sysctl.*' kernel parameter support(*). If we
> > need a kernel cmdline support, I think this is more generic way. But it
> > seems the discussion has been stopped.
>
> It was actually merged in 5.8. So sysctl should be sufficient with that.
> But maybe it's weird to start adding sysctls, when the rest of tracing
> tunables is AFAIK under /sys/kernel/tracing/ ?
>
During the TraceFS meetings Steven runs I was asked to add a boot
parameter and sysctl for user_events to limit the max.
To me, it seems when user_events moves toward namespace awareness
sysctl might be easier to use from within a namespace to turn knobs.
Happy to change to whatever, but I want to see Steven and Masami agree
on the approach before doing so.
Steven, do you agree with Masami to move to just sysctl?
Thanks,
-Beau
>
> > (*) https://patchwork.kernel.org/project/linux-mm/patch/20200427180433.7029-2-vbabka@xxxxxxx/
> >
> > Thank you,
> >
> >>
> >> Signed-off-by: Beau Belgrave <beaub@xxxxxxxxxxxxxxxxxxx>
> >> ---
> >> kernel/trace/trace_events_user.c | 59 ++++++++++++++++++++++++++++++++
> >> 1 file changed, 59 insertions(+)
> >>
> >> diff --git a/kernel/trace/trace_events_user.c b/kernel/trace/trace_events_user.c
> >> index 222f2eb59c7c..6a5ebe243999 100644
> >> --- a/kernel/trace/trace_events_user.c
> >> +++ b/kernel/trace/trace_events_user.c
> >> @@ -20,6 +20,7 @@
> >> #include <linux/types.h>
> >> #include <linux/uaccess.h>
> >> #include <linux/highmem.h>
> >> +#include <linux/init.h>
> >> #include <linux/user_events.h>
> >> #include "trace.h"
> >> #include "trace_dynevent.h"
> >> @@ -61,6 +62,12 @@ struct user_event_group {
> >> /* Group for init_user_ns mapping, top-most group */
> >> static struct user_event_group *init_group;
> >>
> >> +/* Max allowed events for the whole system */
> >> +static unsigned int max_user_events = 32768;
> >> +
> >> +/* Current number of events on the whole system */
> >> +static unsigned int current_user_events;
> >> +
> >> /*
> >> * Stores per-event properties, as users register events
> >> * within a file a user_event might be created if it does not
> >> @@ -1241,6 +1248,8 @@ static int destroy_user_event(struct user_event *user)
> >> {
> >> int ret = 0;
> >>
> >> + lockdep_assert_held(&event_mutex);
> >> +
> >> /* Must destroy fields before call removal */
> >> user_event_destroy_fields(user);
> >>
> >> @@ -1257,6 +1266,11 @@ static int destroy_user_event(struct user_event *user)
> >> kfree(EVENT_NAME(user));
> >> kfree(user);
> >>
> >> + if (current_user_events > 0)
> >> + current_user_events--;
> >> + else
> >> + pr_alert("BUG: Bad current_user_events\n");
> >> +
> >> return ret;
> >> }
> >>
> >> @@ -1744,6 +1758,11 @@ static int user_event_parse(struct user_event_group *group, char *name,
> >>
> >> mutex_lock(&event_mutex);
> >>
> >> + if (current_user_events >= max_user_events) {
> >> + ret = -EMFILE;
> >> + goto put_user_lock;
> >> + }
> >> +
> >> ret = user_event_trace_register(user);
> >>
> >> if (ret)
> >> @@ -1755,6 +1774,7 @@ static int user_event_parse(struct user_event_group *group, char *name,
> >> dyn_event_init(&user->devent, &user_event_dops);
> >> dyn_event_add(&user->devent, &user->call);
> >> hash_add(group->register_table, &user->node, key);
> >> + current_user_events++;
> >>
> >> mutex_unlock(&event_mutex);
> >>
> >> @@ -2386,6 +2406,43 @@ static int create_user_tracefs(void)
> >> return -ENODEV;
> >> }
> >>
> >> +static int __init set_max_user_events(char *str)
> >> +{
> >> + if (!str)
> >> + return 0;
> >> +
> >> + if (kstrtouint(str, 0, &max_user_events))
> >> + return 0;
> >> +
> >> + return 1;
> >> +}
> >> +__setup("user_events_max=", set_max_user_events);
> >> +
> >> +static int set_max_user_events_sysctl(struct ctl_table *table, int write,
> >> + void *buffer, size_t *lenp, loff_t *ppos)
> >> +{
> >> + int ret;
> >> +
> >> + mutex_lock(&event_mutex);
> >> +
> >> + ret = proc_douintvec(table, write, buffer, lenp, ppos);
> >> +
> >> + mutex_unlock(&event_mutex);
> >> +
> >> + return ret;
> >> +}
> >> +
> >> +static struct ctl_table user_event_sysctls[] = {
> >> + {
> >> + .procname = "user_events_max",
> >> + .data = &max_user_events,
> >> + .maxlen = sizeof(unsigned int),
> >> + .mode = 0644,
> >> + .proc_handler = set_max_user_events_sysctl,
> >> + },
> >> + {}
> >> +};
> >> +
> >> static int __init trace_events_user_init(void)
> >> {
> >> int ret;
> >> @@ -2415,6 +2472,8 @@ static int __init trace_events_user_init(void)
> >> if (dyn_event_register(&user_event_dops))
> >> pr_warn("user_events could not register with dyn_events\n");
> >>
> >> + register_sysctl_init("kernel", user_event_sysctls);
> >> +
> >> return 0;
> >> }
> >>
> >> --
> >> 2.25.1
> >>
> >
> >
|