perf: Avoid horrible stack usage

Both Linus (most recent) and Steve (a while ago) reported that perf
related callbacks have massive stack bloat.

The problem is that software events need a pt_regs in order to
properly report the event location and unwind stack. And because we
could not assume one was present we allocated one on stack and filled
it with minimal bits required for operation.

Now, pt_regs is quite large, so this is undesirable. Furthermore it
turns out that most sites actually have a pt_regs pointer available,
making this even more onerous, as the stack space is pointless waste.

This patch addresses the problem by observing that software events
have well defined nesting semantics, therefore we can use static
per-cpu storage instead of on-stack.

Linus made the further observation that all but the scheduler callers
of perf_sw_event() have a pt_regs available, so we change the regular
perf_sw_event() to require a valid pt_regs (where it used to be
optional) and add perf_sw_event_sched() for the scheduler.

We have a scheduler specific call instead of a more generic _noregs()
like construct because we can assume non-recursion from the scheduler
and thereby simplify the code further (_noregs would have to put the
recursion context call inline in order to assertain which __perf_regs
element to use).

One last note on the implementation of perf_trace_buf_prepare(); we
allow .regs = NULL for those cases where we already have a pt_regs
pointer available and do not need another.

Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Reported-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Javi Merino <javi.merino@arm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Petr Mladek <pmladek@suse.cz>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Tom Zanussi <tom.zanussi@linux.intel.com>
Cc: Vaibhav Nagarnaik <vnagarnaik@google.com>
Link: http://lkml.kernel.org/r/20141216115041.GW3337@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/include/linux/ftrace_event.h b/include/linux/ftrace_event.h
index 0bebb5c348b8268eff6135f24f1635c0adf2dbb1..d36f68b08acc1fc95c0df5867df545ac2976d0d6 100644 (file)
--- a/include/linux/ftrace_event.h
+++ b/include/linux/ftrace_event.h
@@ -595,7 +595,7 @@ extern int  ftrace_profile_set_filter(struct perf_event *event, int event_id,
                                     char *filter_str);
 extern void ftrace_profile_free_filter(struct perf_event *event);
 extern void *perf_trace_buf_prepare(int size, unsigned short type,
-                                   struct pt_regs *regs, int *rctxp);
+                                   struct pt_regs **regs, int *rctxp);
 
 static inline void
 perf_trace_buf_submit(void *raw_data, int size, int rctx, u64 addr,

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 4f7a61ca4b393dc837cb4ad278c4a66306247cbd..3a7bd80b4db8b5f8f74f94bfdad17e76389aff77 100644 (file)
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -665,6 +665,7 @@ static inline int is_software_event(struct perf_event *event)
 
 extern struct static_key perf_swevent_enabled[PERF_COUNT_SW_MAX];
 
+extern void ___perf_sw_event(u32, u64, struct pt_regs *, u64);
 extern void __perf_sw_event(u32, u64, struct pt_regs *, u64);
 
 #ifndef perf_arch_fetch_caller_regs
@@ -689,14 +690,25 @@ static inline void perf_fetch_caller_regs(struct pt_regs *regs)
 static __always_inline void
 perf_sw_event(u32 event_id, u64 nr, struct pt_regs *regs, u64 addr)
 {
-       struct pt_regs hot_regs;
+       if (static_key_false(&perf_swevent_enabled[event_id]))
+               __perf_sw_event(event_id, nr, regs, addr);
+}
+
+DECLARE_PER_CPU(struct pt_regs, __perf_regs[4]);
 
+/*
+ * 'Special' version for the scheduler, it hard assumes no recursion,
+ * which is guaranteed by us not actually scheduling inside other swevents
+ * because those disable preemption.
+ */
+static __always_inline void
+perf_sw_event_sched(u32 event_id, u64 nr, u64 addr)
+{
        if (static_key_false(&perf_swevent_enabled[event_id])) {
-               if (!regs) {
-                       perf_fetch_caller_regs(&hot_regs);
-                       regs = &hot_regs;
-               }
-               __perf_sw_event(event_id, nr, regs, addr);
+               struct pt_regs *regs = this_cpu_ptr(&__perf_regs[0]);
+
+               perf_fetch_caller_regs(regs);
+               ___perf_sw_event(event_id, nr, regs, addr);
        }
 }
 
@@ -712,7 +724,7 @@ static inline void perf_event_task_sched_in(struct task_struct *prev,
 static inline void perf_event_task_sched_out(struct task_struct *prev,
                                             struct task_struct *next)
 {
-       perf_sw_event(PERF_COUNT_SW_CONTEXT_SWITCHES, 1, NULL, 0);
+       perf_sw_event_sched(PERF_COUNT_SW_CONTEXT_SWITCHES, 1, 0);
 
        if (static_key_false(&perf_sched_events.key))
                __perf_event_task_sched_out(prev, next);
@@ -823,6 +835,8 @@ static inline int perf_event_refresh(struct perf_event *event, int refresh)
 static inline void
 perf_sw_event(u32 event_id, u64 nr, struct pt_regs *regs, u64 addr)    { }
 static inline void
+perf_sw_event_sched(u32 event_id, u64 nr, u64 addr)                    { }
+static inline void
 perf_bp_event(struct perf_event *event, void *data)                    { }
 
 static inline int perf_register_guest_info_callbacks

diff --git a/include/trace/ftrace.h b/include/trace/ftrace.h
index 139b5067345b2ecb2daa1881d8b484ad76cf382a..27609dfcce25916120521b23215dd473fab0051a 100644 (file)
--- a/include/trace/ftrace.h
+++ b/include/trace/ftrace.h
@@ -763,7 +763,7 @@ perf_trace_##call(void *__data, proto)                                      \
        struct ftrace_event_call *event_call = __data;                  \
        struct ftrace_data_offsets_##call __maybe_unused __data_offsets;\
        struct ftrace_raw_##call *entry;                                \
-       struct pt_regs __regs;                                          \
+       struct pt_regs *__regs;                                         \
        u64 __addr = 0, __count = 1;                                    \
        struct task_struct *__task = NULL;                              \
        struct hlist_head *head;                                        \
@@ -782,18 +782,19 @@ perf_trace_##call(void *__data, proto)                                    \
                             sizeof(u64));                              \
        __entry_size -= sizeof(u32);                                    \
                                                                        \
-       perf_fetch_caller_regs(&__regs);                                \
        entry = perf_trace_buf_prepare(__entry_size,                    \
                        event_call->event.type, &__regs, &rctx);        \
        if (!entry)                                                     \
                return;                                                 \
                                                                        \
+       perf_fetch_caller_regs(__regs);                                 \
+                                                                       \
        tstruct                                                         \
                                                                        \
        { assign; }                                                     \
                                                                        \
        perf_trace_buf_submit(entry, __entry_size, rctx, __addr,        \
-               __count, &__regs, head, __task);                        \
+               __count, __regs, head, __task);                         \
 }
 
 /*

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 882f835a0d859e011848069ed6ee716f3def4dee..c10124b772c44bbf1131c294fb5feaa0bb659a96 100644 (file)
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -5889,6 +5889,8 @@ end:
        rcu_read_unlock();
 }
 
+DEFINE_PER_CPU(struct pt_regs, __perf_regs[4]);
+
 int perf_swevent_get_recursion_context(void)
 {
        struct swevent_htable *swhash = this_cpu_ptr(&swevent_htable);
@@ -5904,21 +5906,30 @@ inline void perf_swevent_put_recursion_context(int rctx)
        put_recursion_context(swhash->recursion, rctx);
 }
 
-void __perf_sw_event(u32 event_id, u64 nr, struct pt_regs *regs, u64 addr)
+void ___perf_sw_event(u32 event_id, u64 nr, struct pt_regs *regs, u64 addr)
 {
        struct perf_sample_data data;
-       int rctx;
 
-       preempt_disable_notrace();
-       rctx = perf_swevent_get_recursion_context();
-       if (rctx < 0)
+       if (WARN_ON_ONCE(!regs))
                return;
 
        perf_sample_data_init(&data, addr, 0);
-
        do_perf_sw_event(PERF_TYPE_SOFTWARE, event_id, nr, &data, regs);
+}
+
+void __perf_sw_event(u32 event_id, u64 nr, struct pt_regs *regs, u64 addr)
+{
+       int rctx;
+
+       preempt_disable_notrace();
+       rctx = perf_swevent_get_recursion_context();
+       if (unlikely(rctx < 0))
+               goto fail;
+
+       ___perf_sw_event(event_id, nr, regs, addr);
 
        perf_swevent_put_recursion_context(rctx);
+fail:
        preempt_enable_notrace();
 }
 

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index c0accc00566eb774a022870635c60e63da6ee198..d22fb16a715397eadcf76a5f42c15cea37985e93 100644 (file)
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1082,7 +1082,7 @@ void set_task_cpu(struct task_struct *p, unsigned int new_cpu)
                if (p->sched_class->migrate_task_rq)
                        p->sched_class->migrate_task_rq(p, new_cpu);
                p->se.nr_migrations++;
-               perf_sw_event(PERF_COUNT_SW_CPU_MIGRATIONS, 1, NULL, 0);
+               perf_sw_event_sched(PERF_COUNT_SW_CPU_MIGRATIONS, 1, 0);
        }
 
        __set_task_cpu(p, new_cpu);

diff --git a/kernel/trace/trace_event_perf.c b/kernel/trace/trace_event_perf.c
index 4b9c114ee9de87d10edd154239c7cb18d237af00..6fa484de2ba1811ada052f451d1bc147e7241068 100644 (file)
--- a/kernel/trace/trace_event_perf.c
+++ b/kernel/trace/trace_event_perf.c
@@ -261,7 +261,7 @@ void perf_trace_del(struct perf_event *p_event, int flags)
 }
 
 void *perf_trace_buf_prepare(int size, unsigned short type,
-                            struct pt_regs *regs, int *rctxp)
+                            struct pt_regs **regs, int *rctxp)
 {
        struct trace_entry *entry;
        unsigned long flags;
@@ -280,6 +280,8 @@ void *perf_trace_buf_prepare(int size, unsigned short type,
        if (*rctxp < 0)
                return NULL;
 
+       if (regs)
+               *regs = this_cpu_ptr(&__perf_regs[*rctxp]);
        raw_data = this_cpu_ptr(perf_trace_buf[*rctxp]);
 
        /* zero the dead bytes from align to not leak stack to user */

diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
index 5edb518be3458a01096351f0562fb84ce5f9b231..296079ae658300123e157d3265fe9e0f5a352bcf 100644 (file)
--- a/kernel/trace/trace_kprobe.c
+++ b/kernel/trace/trace_kprobe.c
@@ -1148,7 +1148,7 @@ kprobe_perf_func(struct trace_kprobe *tk, struct pt_regs *regs)
        size = ALIGN(__size + sizeof(u32), sizeof(u64));
        size -= sizeof(u32);
 
-       entry = perf_trace_buf_prepare(size, call->event.type, regs, &rctx);
+       entry = perf_trace_buf_prepare(size, call->event.type, NULL, &rctx);
        if (!entry)
                return;
 
@@ -1179,7 +1179,7 @@ kretprobe_perf_func(struct trace_kprobe *tk, struct kretprobe_instance *ri,
        size = ALIGN(__size + sizeof(u32), sizeof(u64));
        size -= sizeof(u32);
 
-       entry = perf_trace_buf_prepare(size, call->event.type, regs, &rctx);
+       entry = perf_trace_buf_prepare(size, call->event.type, NULL, &rctx);
        if (!entry)
                return;
 

diff --git a/kernel/trace/trace_syscalls.c b/kernel/trace/trace_syscalls.c
index c6ee36fcbf9071a22e4b86d7ba4b3da3bd047a32..f97f6e3a676ce35b1606b58fc9da694e38d83204 100644 (file)
--- a/kernel/trace/trace_syscalls.c
+++ b/kernel/trace/trace_syscalls.c
@@ -574,7 +574,7 @@ static void perf_syscall_enter(void *ignore, struct pt_regs *regs, long id)
        size -= sizeof(u32);
 
        rec = (struct syscall_trace_enter *)perf_trace_buf_prepare(size,
-                               sys_data->enter_event->event.type, regs, &rctx);
+                               sys_data->enter_event->event.type, NULL, &rctx);
        if (!rec)
                return;
 
@@ -647,7 +647,7 @@ static void perf_syscall_exit(void *ignore, struct pt_regs *regs, long ret)
        size -= sizeof(u32);
 
        rec = (struct syscall_trace_exit *)perf_trace_buf_prepare(size,
-                               sys_data->exit_event->event.type, regs, &rctx);
+                               sys_data->exit_event->event.type, NULL, &rctx);
        if (!rec)
                return;
 

diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
index 8520acc34b185f7cb05fcbc4a2a30685dce0ef13..b11441321e7a473a6e7086f28d791dcd44b8a6f3 100644 (file)
--- a/kernel/trace/trace_uprobe.c
+++ b/kernel/trace/trace_uprobe.c
@@ -1111,7 +1111,7 @@ static void __uprobe_perf_func(struct trace_uprobe *tu,
        if (hlist_empty(head))
                goto out;
 
-       entry = perf_trace_buf_prepare(size, call->event.type, regs, &rctx);
+       entry = perf_trace_buf_prepare(size, call->event.type, NULL, &rctx);
        if (!entry)
                goto out;