![Steven Rostedt (VMware)](/assets/img/avatar_default.png)
The stack tracer records a stack dump whenever it sees a stack usage that is more than what it ever saw before. This can happen at any function that is being traced. If it happens when the CPU is going idle (or other strange locations), RCU may not be watching, and in this case, the recording of the stack trace will trigger a warning. There's been lots of efforts to make hacks to allow stack tracing to proceed even if RCU is not watching, but this only causes more issues to appear. Simply do not trace a stack if RCU is not watching. It probably isn't a bad stack anyway. Acked-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
489 lines
11 KiB
C
489 lines
11 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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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/sched/task_stack.h>
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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/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 <asm/setup.h>
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#include "trace.h"
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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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unsigned stack_trace_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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struct stack_trace stack_trace_max = {
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.max_entries = STACK_TRACE_ENTRIES - 1,
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.entries = &stack_dump_trace[0],
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};
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unsigned long stack_trace_max_size;
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arch_spinlock_t stack_trace_max_lock =
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(arch_spinlock_t)__ARCH_SPIN_LOCK_UNLOCKED;
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DEFINE_PER_CPU(int, disable_stack_tracer);
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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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void stack_trace_print(void)
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{
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long i;
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int size;
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pr_emerg(" Depth Size Location (%d entries)\n"
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" ----- ---- --------\n",
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stack_trace_max.nr_entries);
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for (i = 0; i < stack_trace_max.nr_entries; i++) {
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if (stack_dump_trace[i] == ULONG_MAX)
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break;
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if (i+1 == stack_trace_max.nr_entries ||
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stack_dump_trace[i+1] == ULONG_MAX)
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size = stack_trace_index[i];
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else
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size = stack_trace_index[i] - stack_trace_index[i+1];
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pr_emerg("%3ld) %8d %5d %pS\n", i, stack_trace_index[i],
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size, (void *)stack_dump_trace[i]);
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}
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}
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/*
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* When arch-specific code overrides this function, the following
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* data should be filled up, assuming stack_trace_max_lock is held to
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* prevent concurrent updates.
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* stack_trace_index[]
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* stack_trace_max
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* stack_trace_max_size
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*/
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void __weak
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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; unsigned long *p, *top, *start;
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static int tracer_frame;
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int frame_size = READ_ONCE(tracer_frame);
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int i, x;
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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 <= stack_trace_max_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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/* Can't do this from NMI context (can cause deadlocks) */
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if (in_nmi())
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return;
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local_irq_save(flags);
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arch_spin_lock(&stack_trace_max_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 <= stack_trace_max_size)
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goto out;
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stack_trace_max_size = this_size;
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stack_trace_max.nr_entries = 0;
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stack_trace_max.skip = 3;
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save_stack_trace(&stack_trace_max);
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/* Skip over the overhead of the stack tracer itself */
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for (i = 0; i < stack_trace_max.nr_entries; i++) {
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if (stack_dump_trace[i] == ip)
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break;
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}
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/*
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* Some archs may not have the passed in ip in the dump.
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* If that happens, we need to show everything.
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*/
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if (i == stack_trace_max.nr_entries)
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i = 0;
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/*
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* Now find where in the stack these are.
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*/
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x = 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 < stack_trace_max.nr_entries) {
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int found = 0;
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stack_trace_index[x] = this_size;
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p = start;
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for (; p < top && i < stack_trace_max.nr_entries; p++) {
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if (stack_dump_trace[i] == ULONG_MAX)
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break;
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/*
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* The READ_ONCE_NOCHECK is used to let KASAN know that
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* this is not a stack-out-of-bounds error.
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*/
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if ((READ_ONCE_NOCHECK(*p)) == stack_dump_trace[i]) {
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stack_dump_trace[x] = stack_dump_trace[i++];
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this_size = stack_trace_index[x++] =
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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)) {
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tracer_frame = (p - stack) *
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sizeof(unsigned long);
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stack_trace_max_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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stack_trace_max.nr_entries = x;
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for (; x < i; x++)
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stack_dump_trace[x] = ULONG_MAX;
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if (task_stack_end_corrupted(current)) {
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stack_trace_print();
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BUG();
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}
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out:
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arch_spin_unlock(&stack_trace_max_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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preempt_disable_notrace();
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/* no atomic needed, we only modify this variable by this cpu */
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__this_cpu_inc(disable_stack_tracer);
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if (__this_cpu_read(disable_stack_tracer) != 1)
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goto out;
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/* If rcu is not watching, then save stack trace can fail */
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if (!rcu_is_watching())
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goto out;
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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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__this_cpu_dec(disable_stack_tracer);
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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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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 disable_stack_tracer here.
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*/
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__this_cpu_inc(disable_stack_tracer);
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arch_spin_lock(&stack_trace_max_lock);
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*ptr = val;
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arch_spin_unlock(&stack_trace_max_lock);
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__this_cpu_dec(disable_stack_tracer);
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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 > stack_trace_max.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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local_irq_disable();
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__this_cpu_inc(disable_stack_tracer);
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arch_spin_lock(&stack_trace_max_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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arch_spin_unlock(&stack_trace_max_lock);
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__this_cpu_dec(disable_stack_tracer);
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local_irq_enable();
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}
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static void 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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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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stack_trace_max.nr_entries);
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if (!stack_tracer_enabled && !stack_trace_max_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 >= stack_trace_max.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 == stack_trace_max.nr_entries ||
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stack_dump_trace[i+1] == ULONG_MAX)
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size = stack_trace_index[i];
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else
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size = stack_trace_index[i] - stack_trace_index[i+1];
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seq_printf(m, "%3ld) %8d %5d ", i, stack_trace_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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#ifdef CONFIG_DYNAMIC_FTRACE
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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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struct ftrace_ops *ops = inode->i_private;
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return ftrace_regex_open(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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#endif /* CONFIG_DYNAMIC_FTRACE */
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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 (IS_ERR(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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&stack_trace_max_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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#ifdef CONFIG_DYNAMIC_FTRACE
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trace_create_file("stack_trace_filter", 0444, d_tracer,
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&trace_ops, &stack_trace_filter_fops);
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#endif
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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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