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. (*) 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 > -- Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
