![Aaron Tomlin](/assets/img/avatar_default.png)
It is difficult to detect a stack overrun when it actually occurs. We have observed that this type of corruption is often silent and can go unnoticed. Once the corrupted region is examined, the outcome is undefined and often results in sporadic system crashes. When the stack tracing feature is enabled, let's check for this condition and take appropriate action. Note: init_task doesn't get its stack end location set to STACK_END_MAGIC. Link: http://lkml.kernel.org/r/1395669837-30209-1-git-send-email-atomlin@redhat.com Signed-off-by: Aaron Tomlin <atomlin@redhat.com> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
459 lines
10 KiB
C
459 lines
10 KiB
C
/*
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* Copyright (C) 2008 Steven Rostedt <srostedt@redhat.com>
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*
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*/
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#include <linux/stacktrace.h>
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#include <linux/kallsyms.h>
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#include <linux/seq_file.h>
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#include <linux/spinlock.h>
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#include <linux/uaccess.h>
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#include <linux/debugfs.h>
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#include <linux/ftrace.h>
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#include <linux/module.h>
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#include <linux/sysctl.h>
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#include <linux/init.h>
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#include <linux/fs.h>
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#include <linux/magic.h>
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#include <asm/setup.h>
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#include "trace.h"
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#define STACK_TRACE_ENTRIES 500
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#ifdef CC_USING_FENTRY
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# define fentry 1
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#else
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# define fentry 0
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#endif
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static unsigned long stack_dump_trace[STACK_TRACE_ENTRIES+1] =
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{ [0 ... (STACK_TRACE_ENTRIES)] = ULONG_MAX };
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static unsigned stack_dump_index[STACK_TRACE_ENTRIES];
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/*
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* Reserve one entry for the passed in ip. This will allow
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* us to remove most or all of the stack size overhead
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* added by the stack tracer itself.
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*/
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static struct stack_trace max_stack_trace = {
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.max_entries = STACK_TRACE_ENTRIES - 1,
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.entries = &stack_dump_trace[1],
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};
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static unsigned long max_stack_size;
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static arch_spinlock_t max_stack_lock =
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(arch_spinlock_t)__ARCH_SPIN_LOCK_UNLOCKED;
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static DEFINE_PER_CPU(int, trace_active);
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static DEFINE_MUTEX(stack_sysctl_mutex);
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int stack_tracer_enabled;
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static int last_stack_tracer_enabled;
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static inline void
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check_stack(unsigned long ip, unsigned long *stack)
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{
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unsigned long this_size, flags;
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unsigned long *p, *top, *start;
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static int tracer_frame;
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int frame_size = ACCESS_ONCE(tracer_frame);
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int i;
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this_size = ((unsigned long)stack) & (THREAD_SIZE-1);
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this_size = THREAD_SIZE - this_size;
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/* Remove the frame of the tracer */
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this_size -= frame_size;
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if (this_size <= max_stack_size)
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return;
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/* we do not handle interrupt stacks yet */
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if (!object_is_on_stack(stack))
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return;
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local_irq_save(flags);
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arch_spin_lock(&max_stack_lock);
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/* In case another CPU set the tracer_frame on us */
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if (unlikely(!frame_size))
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this_size -= tracer_frame;
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/* a race could have already updated it */
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if (this_size <= max_stack_size)
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goto out;
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max_stack_size = this_size;
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max_stack_trace.nr_entries = 0;
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max_stack_trace.skip = 3;
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save_stack_trace(&max_stack_trace);
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/*
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* Add the passed in ip from the function tracer.
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* Searching for this on the stack will skip over
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* most of the overhead from the stack tracer itself.
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*/
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stack_dump_trace[0] = ip;
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max_stack_trace.nr_entries++;
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/*
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* Now find where in the stack these are.
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*/
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i = 0;
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start = stack;
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top = (unsigned long *)
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(((unsigned long)start & ~(THREAD_SIZE-1)) + THREAD_SIZE);
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/*
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* Loop through all the entries. One of the entries may
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* for some reason be missed on the stack, so we may
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* have to account for them. If they are all there, this
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* loop will only happen once. This code only takes place
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* on a new max, so it is far from a fast path.
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*/
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while (i < max_stack_trace.nr_entries) {
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int found = 0;
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stack_dump_index[i] = this_size;
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p = start;
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for (; p < top && i < max_stack_trace.nr_entries; p++) {
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if (*p == stack_dump_trace[i]) {
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this_size = stack_dump_index[i++] =
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(top - p) * sizeof(unsigned long);
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found = 1;
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/* Start the search from here */
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start = p + 1;
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/*
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* We do not want to show the overhead
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* of the stack tracer stack in the
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* max stack. If we haven't figured
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* out what that is, then figure it out
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* now.
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*/
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if (unlikely(!tracer_frame) && i == 1) {
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tracer_frame = (p - stack) *
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sizeof(unsigned long);
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max_stack_size -= tracer_frame;
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}
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}
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}
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if (!found)
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i++;
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}
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BUG_ON(current != &init_task &&
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*(end_of_stack(current)) != STACK_END_MAGIC);
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out:
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arch_spin_unlock(&max_stack_lock);
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local_irq_restore(flags);
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}
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static void
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stack_trace_call(unsigned long ip, unsigned long parent_ip,
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struct ftrace_ops *op, struct pt_regs *pt_regs)
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{
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unsigned long stack;
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int cpu;
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preempt_disable_notrace();
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cpu = raw_smp_processor_id();
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/* no atomic needed, we only modify this variable by this cpu */
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if (per_cpu(trace_active, cpu)++ != 0)
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goto out;
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/*
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* When fentry is used, the traced function does not get
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* its stack frame set up, and we lose the parent.
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* The ip is pretty useless because the function tracer
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* was called before that function set up its stack frame.
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* In this case, we use the parent ip.
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*
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* By adding the return address of either the parent ip
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* or the current ip we can disregard most of the stack usage
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* caused by the stack tracer itself.
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*
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* The function tracer always reports the address of where the
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* mcount call was, but the stack will hold the return address.
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*/
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if (fentry)
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ip = parent_ip;
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else
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ip += MCOUNT_INSN_SIZE;
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check_stack(ip, &stack);
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out:
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per_cpu(trace_active, cpu)--;
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/* prevent recursion in schedule */
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preempt_enable_notrace();
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}
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static struct ftrace_ops trace_ops __read_mostly =
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{
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.func = stack_trace_call,
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.flags = FTRACE_OPS_FL_RECURSION_SAFE,
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};
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static ssize_t
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stack_max_size_read(struct file *filp, char __user *ubuf,
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size_t count, loff_t *ppos)
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{
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unsigned long *ptr = filp->private_data;
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char buf[64];
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int r;
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r = snprintf(buf, sizeof(buf), "%ld\n", *ptr);
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if (r > sizeof(buf))
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r = sizeof(buf);
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return simple_read_from_buffer(ubuf, count, ppos, buf, r);
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}
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static ssize_t
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stack_max_size_write(struct file *filp, const char __user *ubuf,
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size_t count, loff_t *ppos)
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{
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long *ptr = filp->private_data;
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unsigned long val, flags;
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int ret;
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int cpu;
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ret = kstrtoul_from_user(ubuf, count, 10, &val);
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if (ret)
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return ret;
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local_irq_save(flags);
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/*
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* In case we trace inside arch_spin_lock() or after (NMI),
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* we will cause circular lock, so we also need to increase
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* the percpu trace_active here.
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*/
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cpu = smp_processor_id();
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per_cpu(trace_active, cpu)++;
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arch_spin_lock(&max_stack_lock);
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*ptr = val;
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arch_spin_unlock(&max_stack_lock);
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per_cpu(trace_active, cpu)--;
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local_irq_restore(flags);
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return count;
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}
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static const struct file_operations stack_max_size_fops = {
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.open = tracing_open_generic,
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.read = stack_max_size_read,
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.write = stack_max_size_write,
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.llseek = default_llseek,
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};
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static void *
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__next(struct seq_file *m, loff_t *pos)
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{
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long n = *pos - 1;
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if (n >= max_stack_trace.nr_entries || stack_dump_trace[n] == ULONG_MAX)
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return NULL;
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m->private = (void *)n;
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return &m->private;
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}
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static void *
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t_next(struct seq_file *m, void *v, loff_t *pos)
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{
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(*pos)++;
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return __next(m, pos);
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}
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static void *t_start(struct seq_file *m, loff_t *pos)
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{
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int cpu;
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local_irq_disable();
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cpu = smp_processor_id();
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per_cpu(trace_active, cpu)++;
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arch_spin_lock(&max_stack_lock);
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if (*pos == 0)
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return SEQ_START_TOKEN;
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return __next(m, pos);
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}
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static void t_stop(struct seq_file *m, void *p)
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{
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int cpu;
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arch_spin_unlock(&max_stack_lock);
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cpu = smp_processor_id();
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per_cpu(trace_active, cpu)--;
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local_irq_enable();
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}
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static int trace_lookup_stack(struct seq_file *m, long i)
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{
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unsigned long addr = stack_dump_trace[i];
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return seq_printf(m, "%pS\n", (void *)addr);
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}
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static void print_disabled(struct seq_file *m)
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{
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seq_puts(m, "#\n"
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"# Stack tracer disabled\n"
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"#\n"
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"# To enable the stack tracer, either add 'stacktrace' to the\n"
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"# kernel command line\n"
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"# or 'echo 1 > /proc/sys/kernel/stack_tracer_enabled'\n"
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"#\n");
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}
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static int t_show(struct seq_file *m, void *v)
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{
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long i;
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int size;
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if (v == SEQ_START_TOKEN) {
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seq_printf(m, " Depth Size Location"
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" (%d entries)\n"
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" ----- ---- --------\n",
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max_stack_trace.nr_entries - 1);
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if (!stack_tracer_enabled && !max_stack_size)
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print_disabled(m);
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return 0;
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}
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i = *(long *)v;
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if (i >= max_stack_trace.nr_entries ||
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stack_dump_trace[i] == ULONG_MAX)
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return 0;
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if (i+1 == max_stack_trace.nr_entries ||
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stack_dump_trace[i+1] == ULONG_MAX)
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size = stack_dump_index[i];
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else
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size = stack_dump_index[i] - stack_dump_index[i+1];
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seq_printf(m, "%3ld) %8d %5d ", i, stack_dump_index[i], size);
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trace_lookup_stack(m, i);
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return 0;
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}
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static const struct seq_operations stack_trace_seq_ops = {
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.start = t_start,
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.next = t_next,
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.stop = t_stop,
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.show = t_show,
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};
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static int stack_trace_open(struct inode *inode, struct file *file)
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{
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return seq_open(file, &stack_trace_seq_ops);
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}
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static const struct file_operations stack_trace_fops = {
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.open = stack_trace_open,
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.read = seq_read,
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.llseek = seq_lseek,
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.release = seq_release,
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};
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static int
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stack_trace_filter_open(struct inode *inode, struct file *file)
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{
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return ftrace_regex_open(&trace_ops, FTRACE_ITER_FILTER,
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inode, file);
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}
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static const struct file_operations stack_trace_filter_fops = {
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.open = stack_trace_filter_open,
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.read = seq_read,
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.write = ftrace_filter_write,
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.llseek = tracing_lseek,
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.release = ftrace_regex_release,
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};
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int
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stack_trace_sysctl(struct ctl_table *table, int write,
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void __user *buffer, size_t *lenp,
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loff_t *ppos)
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{
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int ret;
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mutex_lock(&stack_sysctl_mutex);
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ret = proc_dointvec(table, write, buffer, lenp, ppos);
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if (ret || !write ||
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(last_stack_tracer_enabled == !!stack_tracer_enabled))
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goto out;
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last_stack_tracer_enabled = !!stack_tracer_enabled;
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if (stack_tracer_enabled)
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register_ftrace_function(&trace_ops);
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else
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unregister_ftrace_function(&trace_ops);
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out:
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mutex_unlock(&stack_sysctl_mutex);
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return ret;
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}
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static char stack_trace_filter_buf[COMMAND_LINE_SIZE+1] __initdata;
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static __init int enable_stacktrace(char *str)
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{
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if (strncmp(str, "_filter=", 8) == 0)
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strncpy(stack_trace_filter_buf, str+8, COMMAND_LINE_SIZE);
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stack_tracer_enabled = 1;
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last_stack_tracer_enabled = 1;
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return 1;
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}
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__setup("stacktrace", enable_stacktrace);
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static __init int stack_trace_init(void)
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{
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struct dentry *d_tracer;
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d_tracer = tracing_init_dentry();
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if (!d_tracer)
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return 0;
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trace_create_file("stack_max_size", 0644, d_tracer,
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&max_stack_size, &stack_max_size_fops);
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trace_create_file("stack_trace", 0444, d_tracer,
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NULL, &stack_trace_fops);
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trace_create_file("stack_trace_filter", 0444, d_tracer,
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NULL, &stack_trace_filter_fops);
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if (stack_trace_filter_buf[0])
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ftrace_set_early_filter(&trace_ops, stack_trace_filter_buf, 1);
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if (stack_tracer_enabled)
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register_ftrace_function(&trace_ops);
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return 0;
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}
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device_initcall(stack_trace_init);
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