[PATCH/RFC] perf core: Allow setting up max frame stack depth via sysctl

From: Arnaldo Carvalho de Melo
Date: Wed Apr 20 2016 - 18:47:42 EST

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The default remains 127, which is good for most cases, and not even hit
most of the time, but then for some cases, as reported by Brendan, 1024+
deep frames are appearing on the radar for things like groovy, ruby.

And in some workloads putting a _lower_ cap on this may make sense. One
that is per event still needs to be put in place tho.

The new file is:

# cat /proc/sys/kernel/perf_event_max_stack
127

Chaging it:

# echo 256 > /proc/sys/kernel/perf_event_max_stack
# cat /proc/sys/kernel/perf_event_max_stack
256

But as soon as there is some event using callchains we get:

# echo 512 > /proc/sys/kernel/perf_event_max_stack
-bash: echo: write error: Device or resource busy
#

Because we only allocate the callchain percpu data structures when there
is a user, which allows for changing the max easily, its just a matter
of having no callchain users at that point.

Reported-by: Brendan Gregg <brendan.d.gregg@xxxxxxxxx>
Link: http://lkml.kernel.org/n/tip-cgls6uuncwjtq969tys1j6b0@xxxxxxxxxxxxxx
Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>

diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt
index 57653a44b128..260cde08e92e 100644
--- a/Documentation/sysctl/kernel.txt
+++ b/Documentation/sysctl/kernel.txt
@@ -60,6 +60,7 @@ show up in /proc/sys/kernel:
- panic_on_warn
- perf_cpu_time_max_percent
- perf_event_paranoid
+- perf_event_max_stack
- pid_max
- powersave-nap [ PPC only ]
- printk
@@ -654,6 +655,19 @@ users (without CAP_SYS_ADMIN). The default value is 1.

==============================================================

+perf_event_max_stack:
+
+Controls maximum number of stack frames to copy for (attr.sample_type &
+PERF_SAMPLE_CALLCHAIN) configured events, for instance, when using
+'perf record -g' or 'perf trace --call-graph fp'.
+
+This can only be done when no events are in use that have callchains
+enabled, otherwise writing to this file will return -EBUSY.
+
+The default value is 127.
+
+==============================================================
+
pid_max:

PID allocation wrap value. When the kernel's next PID value
diff --git a/arch/arm/kernel/perf_callchain.c b/arch/arm/kernel/perf_callchain.c
index 4e02ae5950ff..27563befa8a2 100644
--- a/arch/arm/kernel/perf_callchain.c
+++ b/arch/arm/kernel/perf_callchain.c
@@ -75,7 +75,7 @@ perf_callchain_user(struct perf_callchain_entry *entry, struct pt_regs *regs)

tail = (struct frame_tail __user *)regs->ARM_fp - 1;

- while ((entry->nr < PERF_MAX_STACK_DEPTH) &&
+ while ((entry->nr < sysctl_perf_event_max_stack) &&
tail && !((unsigned long)tail & 0x3))
tail = user_backtrace(tail, entry);
}
diff --git a/arch/arm64/kernel/perf_callchain.c b/arch/arm64/kernel/perf_callchain.c
index ff4665462a02..32c3c6e70119 100644
--- a/arch/arm64/kernel/perf_callchain.c
+++ b/arch/arm64/kernel/perf_callchain.c
@@ -122,7 +122,7 @@ void perf_callchain_user(struct perf_callchain_entry *entry,

tail = (struct frame_tail __user *)regs->regs[29];

- while (entry->nr < PERF_MAX_STACK_DEPTH &&
+ while (entry->nr < sysctl_perf_event_max_stack &&
tail && !((unsigned long)tail & 0xf))
tail = user_backtrace(tail, entry);
} else {
@@ -132,7 +132,7 @@ void perf_callchain_user(struct perf_callchain_entry *entry,

tail = (struct compat_frame_tail __user *)regs->compat_fp - 1;

- while ((entry->nr < PERF_MAX_STACK_DEPTH) &&
+ while ((entry->nr < sysctl_perf_event_max_stack) &&
tail && !((unsigned long)tail & 0x3))
tail = compat_user_backtrace(tail, entry);
#endif
diff --git a/arch/metag/kernel/perf_callchain.c b/arch/metag/kernel/perf_callchain.c
index 315633461a94..252abc12a5a3 100644
--- a/arch/metag/kernel/perf_callchain.c
+++ b/arch/metag/kernel/perf_callchain.c
@@ -65,7 +65,7 @@ perf_callchain_user(struct perf_callchain_entry *entry, struct pt_regs *regs)

--frame;

- while ((entry->nr < PERF_MAX_STACK_DEPTH) && frame)
+ while ((entry->nr < sysctl_perf_event_max_stack) && frame)
frame = user_backtrace(frame, entry);
}

diff --git a/arch/mips/kernel/perf_event.c b/arch/mips/kernel/perf_event.c
index c1cf9c6c3f77..5021c546ad07 100644
--- a/arch/mips/kernel/perf_event.c
+++ b/arch/mips/kernel/perf_event.c
@@ -35,7 +35,7 @@ static void save_raw_perf_callchain(struct perf_callchain_entry *entry,
addr = *sp++;
if (__kernel_text_address(addr)) {
perf_callchain_store(entry, addr);
- if (entry->nr >= PERF_MAX_STACK_DEPTH)
+ if (entry->nr >= sysctl_perf_event_max_stack)
break;
}
}
@@ -59,7 +59,7 @@ void perf_callchain_kernel(struct perf_callchain_entry *entry,
}
do {
perf_callchain_store(entry, pc);
- if (entry->nr >= PERF_MAX_STACK_DEPTH)
+ if (entry->nr >= sysctl_perf_event_max_stack)
break;
pc = unwind_stack(current, &sp, pc, &ra);
} while (pc);
diff --git a/arch/powerpc/perf/callchain.c b/arch/powerpc/perf/callchain.c
index e04a6752b399..22d9015c1acc 100644
--- a/arch/powerpc/perf/callchain.c
+++ b/arch/powerpc/perf/callchain.c
@@ -247,7 +247,7 @@ static void perf_callchain_user_64(struct perf_callchain_entry *entry,
sp = regs->gpr[1];
perf_callchain_store(entry, next_ip);

- while (entry->nr < PERF_MAX_STACK_DEPTH) {
+ while (entry->nr < sysctl_perf_event_max_stack) {
fp = (unsigned long __user *) sp;
if (!valid_user_sp(sp, 1) || read_user_stack_64(fp, &next_sp))
return;
@@ -453,7 +453,7 @@ static void perf_callchain_user_32(struct perf_callchain_entry *entry,
sp = regs->gpr[1];
perf_callchain_store(entry, next_ip);

- while (entry->nr < PERF_MAX_STACK_DEPTH) {
+ while (entry->nr < sysctl_perf_event_max_stack) {
fp = (unsigned int __user *) (unsigned long) sp;
if (!valid_user_sp(sp, 0) || read_user_stack_32(fp, &next_sp))
return;
diff --git a/arch/sparc/kernel/perf_event.c b/arch/sparc/kernel/perf_event.c
index 6596f66ce112..a4b8b5aed21c 100644
--- a/arch/sparc/kernel/perf_event.c
+++ b/arch/sparc/kernel/perf_event.c
@@ -1756,7 +1756,7 @@ void perf_callchain_kernel(struct perf_callchain_entry *entry,
}
}
#endif
- } while (entry->nr < PERF_MAX_STACK_DEPTH);
+ } while (entry->nr < sysctl_perf_event_max_stack);
}

static inline int
@@ -1790,7 +1790,7 @@ static void perf_callchain_user_64(struct perf_callchain_entry *entry,
pc = sf.callers_pc;
ufp = (unsigned long)sf.fp + STACK_BIAS;
perf_callchain_store(entry, pc);
- } while (entry->nr < PERF_MAX_STACK_DEPTH);
+ } while (entry->nr < sysctl_perf_event_max_stack);
}

static void perf_callchain_user_32(struct perf_callchain_entry *entry,
@@ -1822,7 +1822,7 @@ static void perf_callchain_user_32(struct perf_callchain_entry *entry,
ufp = (unsigned long)sf.fp;
}
perf_callchain_store(entry, pc);
- } while (entry->nr < PERF_MAX_STACK_DEPTH);
+ } while (entry->nr < sysctl_perf_event_max_stack);
}

void
diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
index 041e442a3e28..41d93d0e972b 100644
--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c
@@ -2277,7 +2277,7 @@ perf_callchain_user32(struct pt_regs *regs, struct perf_callchain_entry *entry)

fp = compat_ptr(ss_base + regs->bp);
pagefault_disable();
- while (entry->nr < PERF_MAX_STACK_DEPTH) {
+ while (entry->nr < sysctl_perf_event_max_stack) {
unsigned long bytes;
frame.next_frame = 0;
frame.return_address = 0;
@@ -2337,7 +2337,7 @@ perf_callchain_user(struct perf_callchain_entry *entry, struct pt_regs *regs)
return;

pagefault_disable();
- while (entry->nr < PERF_MAX_STACK_DEPTH) {
+ while (entry->nr < sysctl_perf_event_max_stack) {
unsigned long bytes;
frame.next_frame = NULL;
frame.return_address = 0;
diff --git a/arch/xtensa/kernel/perf_event.c b/arch/xtensa/kernel/perf_event.c
index 54f01188c29c..a6b00b3af429 100644
--- a/arch/xtensa/kernel/perf_event.c
+++ b/arch/xtensa/kernel/perf_event.c
@@ -332,14 +332,14 @@ static int callchain_trace(struct stackframe *frame, void *data)
void perf_callchain_kernel(struct perf_callchain_entry *entry,
struct pt_regs *regs)
{
- xtensa_backtrace_kernel(regs, PERF_MAX_STACK_DEPTH,
+ xtensa_backtrace_kernel(regs, sysctl_perf_event_max_stack,
callchain_trace, NULL, entry);
}

void perf_callchain_user(struct perf_callchain_entry *entry,
struct pt_regs *regs)
{
- xtensa_backtrace_user(regs, PERF_MAX_STACK_DEPTH,
+ xtensa_backtrace_user(regs, sysctl_perf_event_max_stack,
callchain_trace, entry);
}

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index b8b195fbe787..d599ed32af92 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -58,7 +58,7 @@ struct perf_guest_info_callbacks {

struct perf_callchain_entry {
__u64 nr;
- __u64 ip[PERF_MAX_STACK_DEPTH];
+ __u64 ip[0]; /* /proc/sys/kernel/perf_event_max_stack */
};

struct perf_raw_record {
@@ -983,9 +983,11 @@ get_perf_callchain(struct pt_regs *regs, u32 init_nr, bool kernel, bool user,
extern int get_callchain_buffers(void);
extern void put_callchain_buffers(void);

+extern int sysctl_perf_event_max_stack;
+
static inline int perf_callchain_store(struct perf_callchain_entry *entry, u64 ip)
{
- if (entry->nr < PERF_MAX_STACK_DEPTH) {
+ if (entry->nr < sysctl_perf_event_max_stack) {
entry->ip[entry->nr++] = ip;
return 0;
} else {
@@ -1007,6 +1009,8 @@ extern int perf_cpu_time_max_percent_handler(struct ctl_table *table, int write,
void __user *buffer, size_t *lenp,
loff_t *ppos);

+int perf_event_max_stack_handler(struct ctl_table *table, int write,
+ void __user *buffer, size_t *lenp, loff_t *ppos);

static inline bool perf_paranoid_tracepoint_raw(void)
{
diff --git a/kernel/events/callchain.c b/kernel/events/callchain.c
index 343c22f5e867..1390747b2195 100644
--- a/kernel/events/callchain.c
+++ b/kernel/events/callchain.c
@@ -18,6 +18,14 @@ struct callchain_cpus_entries {
struct perf_callchain_entry *cpu_entries[0];
};

+int sysctl_perf_event_max_stack __read_mostly = PERF_MAX_STACK_DEPTH;
+
+static size_t perf_callchain_entry__sizeof(void)
+{
+ return sizeof(struct perf_callchain_entry) +
+ sizeof(__u64) * sysctl_perf_event_max_stack;
+}
+
static DEFINE_PER_CPU(int, callchain_recursion[PERF_NR_CONTEXTS]);
static atomic_t nr_callchain_events;
static DEFINE_MUTEX(callchain_mutex);
@@ -73,7 +81,7 @@ static int alloc_callchain_buffers(void)
if (!entries)
return -ENOMEM;

- size = sizeof(struct perf_callchain_entry) * PERF_NR_CONTEXTS;
+ size = perf_callchain_entry__sizeof() * PERF_NR_CONTEXTS;

for_each_possible_cpu(cpu) {
entries->cpu_entries[cpu] = kmalloc_node(size, GFP_KERNEL,
@@ -215,3 +223,25 @@ exit_put:

return entry;
}
+
+int perf_event_max_stack_handler(struct ctl_table *table, int write,
+ void __user *buffer, size_t *lenp, loff_t *ppos)
+{
+ int new_value = sysctl_perf_event_max_stack, ret;
+ struct ctl_table new_table = *table;
+
+ new_table.data = &new_value;
+ ret = proc_dointvec_minmax(&new_table, write, buffer, lenp, ppos);
+ if (ret || !write)
+ return ret;
+
+ mutex_lock(&callchain_mutex);
+ if (atomic_read(&nr_callchain_events))
+ ret = -EBUSY;
+ else
+ sysctl_perf_event_max_stack = new_value;
+
+ mutex_unlock(&callchain_mutex);
+
+ return ret;
+}
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 725587f10667..afbe9fb32ec5 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -1144,6 +1144,14 @@ static struct ctl_table kern_table[] = {
.extra1 = &zero,
.extra2 = &one_hundred,
},
+ {
+ .procname = "perf_event_max_stack",
+ .data = NULL, /* filled in by handler */
+ .maxlen = sizeof(sysctl_perf_event_max_stack),
+ .mode = 0644,
+ .proc_handler = perf_event_max_stack_handler,
+ .extra1 = &zero,
+ },
#endif
#ifdef CONFIG_KMEMCHECK
{

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