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ftrace: Add recording of functions that caused recursion 

This adds CONFIG_FTRACE_RECORD_RECURSION that will record to a file
"recursed_functions" all the functions that caused recursion while a
callback to the function tracer was running.

Link: https://lkml.kernel.org/r/20201106023548.102375687@goodmis.org

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Guo Ren <guoren@kernel.org>
Cc: "James E.J. Bottomley" <James.Bottomley@HansenPartnership.com>
Cc: Helge Deller <deller@gmx.de>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: x86@kernel.org
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Anton Vorontsov <anton@enomsg.org>
Cc: Colin Cross <ccross@android.com>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Jiri Kosina <jikos@kernel.org>
Cc: Miroslav Benes <mbenes@suse.cz>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Joe Lawrence <joe.lawrence@redhat.com>
Cc: Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>
Cc: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: linux-doc@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: linux-csky@vger.kernel.org
Cc: linux-parisc@vger.kernel.org
Cc: linuxppc-dev@lists.ozlabs.org
Cc: linux-s390@vger.kernel.org
Cc: live-patching@vger.kernel.org
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
This commit is contained in:
Steven Rostedt (VMware) 2020-11-05 21:32:46 -05:00
parent a25d036d93
commit 773c167050
17 changed files with 306 additions and 20 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
Documentation/trace/ftrace-uses.rst
View File

@ -118,7 +118,7 @@ can help in this regard. If you start your code with:
int bit;
bit = ftrace_test_recursion_trylock();
bit = ftrace_test_recursion_trylock(ip, parent_ip);
if (bit < 0)
return;
@ -130,7 +130,9 @@ The code in between will be safe to use, even if it ends up calling a
function that the callback is tracing. Note, on success,
ftrace_test_recursion_trylock() will disable preemption, and the
ftrace_test_recursion_unlock() will enable it again (if it was previously
enabled).
enabled). The instruction pointer (ip) and its parent (parent_ip) is passed to
ftrace_test_recursion_trylock() to record where the recursion happened
(if CONFIG_FTRACE_RECORD_RECURSION is set).
Alternatively, if the FTRACE_OPS_FL_RECURSION flag is set on the ftrace_ops
(as explained below), then a helper trampoline will be used to test

2
arch/csky/kernel/probes/ftrace.c
View File

@ -18,7 +18,7 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
struct kprobe *p;
struct kprobe_ctlblk *kcb;
bit = ftrace_test_recursion_trylock();
bit = ftrace_test_recursion_trylock(ip, parent_ip);
if (bit < 0)
return;

2
arch/parisc/kernel/ftrace.c
View File

@ -210,7 +210,7 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
struct kprobe *p;
int bit;
bit = ftrace_test_recursion_trylock();
bit = ftrace_test_recursion_trylock(ip, parent_ip);
if (bit < 0)
return;

2
arch/powerpc/kernel/kprobes-ftrace.c
View File

@ -20,7 +20,7 @@ void kprobe_ftrace_handler(unsigned long nip, unsigned long parent_nip,
struct kprobe_ctlblk *kcb;
int bit;
bit = ftrace_test_recursion_trylock();
bit = ftrace_test_recursion_trylock(nip, parent_nip);
if (bit < 0)
return;

2
arch/s390/kernel/ftrace.c
View File

@ -204,7 +204,7 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
struct kprobe *p;
int bit;
bit = ftrace_test_recursion_trylock();
bit = ftrace_test_recursion_trylock(ip, parent_ip);
if (bit < 0)
return;

2
arch/x86/kernel/kprobes/ftrace.c
View File

@ -20,7 +20,7 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
struct kprobe_ctlblk *kcb;
int bit;
bit = ftrace_test_recursion_trylock();
bit = ftrace_test_recursion_trylock(ip, parent_ip);
if (bit < 0)
return;

2
fs/pstore/ftrace.c
View File

@ -41,7 +41,7 @@ static void notrace pstore_ftrace_call(unsigned long ip,
if (unlikely(oops_in_progress))
return;
bit = ftrace_test_recursion_trylock();
bit = ftrace_test_recursion_trylock(ip, parent_ip);
if (bit < 0)
return;

29
include/linux/trace_recursion.h
View File

@ -91,6 +91,9 @@ enum {
* not be correct. Allow for a single recursion to cover this case.
*/
TRACE_TRANSITION_BIT,
/* Used to prevent recursion recording from recursing. */
TRACE_RECORD_RECURSION_BIT,
};
#define trace_recursion_set(bit) do { (current)->trace_recursion |= (1<<(bit)); } while (0)
@ -142,7 +145,22 @@ static __always_inline int trace_get_context_bit(void)
pc & HARDIRQ_MASK ? TRACE_CTX_IRQ : TRACE_CTX_SOFTIRQ;
}
static __always_inline int trace_test_and_set_recursion(int start, int max)
#ifdef CONFIG_FTRACE_RECORD_RECURSION
extern void ftrace_record_recursion(unsigned long ip, unsigned long parent_ip);
# define do_ftrace_record_recursion(ip, pip) \
do { \
if (!trace_recursion_test(TRACE_RECORD_RECURSION_BIT)) { \
trace_recursion_set(TRACE_RECORD_RECURSION_BIT); \
ftrace_record_recursion(ip, pip); \
trace_recursion_clear(TRACE_RECORD_RECURSION_BIT); \
} \
} while (0)
#else
# define do_ftrace_record_recursion(ip, pip) do { } while (0)
#endif
static __always_inline int trace_test_and_set_recursion(unsigned long ip, unsigned long pip,
int start, int max)
{
unsigned int val = current->trace_recursion;
int bit;
@ -158,8 +176,10 @@ static __always_inline int trace_test_and_set_recursion(int start, int max)
* a switch between contexts. Allow for a single recursion.
*/
bit = TRACE_TRANSITION_BIT;
if (trace_recursion_test(bit))
if (trace_recursion_test(bit)) {
do_ftrace_record_recursion(ip, pip);
return -1;
}
trace_recursion_set(bit);
barrier();
return bit + 1;
@ -199,9 +219,10 @@ static __always_inline void trace_clear_recursion(int bit)
* Returns: -1 if a recursion happened.
* >= 0 if no recursion
*/
static __always_inline int ftrace_test_recursion_trylock(void)
static __always_inline int ftrace_test_recursion_trylock(unsigned long ip,
unsigned long parent_ip)
{
return trace_test_and_set_recursion(TRACE_FTRACE_START, TRACE_FTRACE_MAX);
return trace_test_and_set_recursion(ip, parent_ip, TRACE_FTRACE_START, TRACE_FTRACE_MAX);
}
/**

2
kernel/livepatch/patch.c
View File

@ -49,7 +49,7 @@ static void notrace klp_ftrace_handler(unsigned long ip,
ops = container_of(fops, struct klp_ops, fops);
bit = ftrace_test_recursion_trylock();
bit = ftrace_test_recursion_trylock(ip, parent_ip);
if (WARN_ON_ONCE(bit < 0))
return;
/*

25
kernel/trace/Kconfig
View File

@ -727,6 +727,31 @@ config TRACE_EVAL_MAP_FILE
If unsure, say N.
config FTRACE_RECORD_RECURSION
bool "Record functions that recurse in function tracing"
depends on FUNCTION_TRACER
help
All callbacks that attach to the function tracing have some sort
of protection against recursion. Even though the protection exists,
it adds overhead. This option will create a file in the tracefs
file system called "recursed_functions" that will list the functions
that triggered a recursion.
This will add more overhead to cases that have recursion.
If unsure, say N
config FTRACE_RECORD_RECURSION_SIZE
int "Max number of recursed functions to record"
default 128
depends on FTRACE_RECORD_RECURSION
help
This defines the limit of number of functions that can be
listed in the "recursed_functions" file, that lists all
the functions that caused a recursion to happen.
This file can be reset, but the limit can not change in
size at runtime.
config GCOV_PROFILE_FTRACE
bool "Enable GCOV profiling on ftrace subsystem"
depends on GCOV_KERNEL

1
kernel/trace/Makefile
View File

@ -92,6 +92,7 @@ obj-$(CONFIG_DYNAMIC_EVENTS) += trace_dynevent.o
obj-$(CONFIG_PROBE_EVENTS) += trace_probe.o
obj-$(CONFIG_UPROBE_EVENTS) += trace_uprobe.o
obj-$(CONFIG_BOOTTIME_TRACING) += trace_boot.o
obj-$(CONFIG_FTRACE_RECORD_RECURSION) += trace_recursion_record.o
obj-$(CONFIG_TRACEPOINT_BENCHMARK) += trace_benchmark.o

4
kernel/trace/ftrace.c
View File

@ -6918,7 +6918,7 @@ __ftrace_ops_list_func(unsigned long ip, unsigned long parent_ip,
struct ftrace_ops *op;
int bit;
bit = trace_test_and_set_recursion(TRACE_LIST_START, TRACE_LIST_MAX);
bit = trace_test_and_set_recursion(ip, parent_ip, TRACE_LIST_START, TRACE_LIST_MAX);
if (bit < 0)
return;
@ -6993,7 +6993,7 @@ static void ftrace_ops_assist_func(unsigned long ip, unsigned long parent_ip,
{
int bit;
bit = trace_test_and_set_recursion(TRACE_LIST_START, TRACE_LIST_MAX);
bit = trace_test_and_set_recursion(ip, parent_ip, TRACE_LIST_START, TRACE_LIST_MAX);
if (bit < 0)
return;

2
kernel/trace/trace_event_perf.c
View File

@ -447,7 +447,7 @@ perf_ftrace_function_call(unsigned long ip, unsigned long parent_ip,
if ((unsigned long)ops->private != smp_processor_id())
return;
bit = ftrace_test_recursion_trylock();
bit = ftrace_test_recursion_trylock(ip, parent_ip);
if (bit < 0)
return;

2
kernel/trace/trace_functions.c
View File

@ -141,7 +141,7 @@ function_trace_call(unsigned long ip, unsigned long parent_ip,
if (unlikely(!tr->function_enabled))
return;
bit = ftrace_test_recursion_trylock();
bit = ftrace_test_recursion_trylock(ip, parent_ip);
if (bit < 0)
return;

6
kernel/trace/trace_output.c
View File

@ -353,8 +353,8 @@ static inline const char *kretprobed(const char *name)
}
#endif /* CONFIG_KRETPROBES */
static void
seq_print_sym(struct trace_seq *s, unsigned long address, bool offset)
void
trace_seq_print_sym(struct trace_seq *s, unsigned long address, bool offset)
{
#ifdef CONFIG_KALLSYMS
char str[KSYM_SYMBOL_LEN];
@ -420,7 +420,7 @@ seq_print_ip_sym(struct trace_seq *s, unsigned long ip, unsigned long sym_flags)
goto out;
}
seq_print_sym(s, ip, sym_flags & TRACE_ITER_SYM_OFFSET);
trace_seq_print_sym(s, ip, sym_flags & TRACE_ITER_SYM_OFFSET);
if (sym_flags & TRACE_ITER_SYM_ADDR)
trace_seq_printf(s, " <" IP_FMT ">", ip);

1
kernel/trace/trace_output.h
View File

@ -16,6 +16,7 @@ extern int
seq_print_ip_sym(struct trace_seq *s, unsigned long ip,
unsigned long sym_flags);
extern void trace_seq_print_sym(struct trace_seq *s, unsigned long address, bool offset);
extern int trace_print_context(struct trace_iterator *iter);
extern int trace_print_lat_context(struct trace_iterator *iter);

236
kernel/trace/trace_recursion_record.c Normal file
View File

@ -0,0 +1,236 @@
// SPDX-License-Identifier: GPL-2.0
#include <linux/seq_file.h>
#include <linux/kallsyms.h>
#include <linux/module.h>
#include <linux/ftrace.h>
#include <linux/fs.h>
#include "trace_output.h"
struct recursed_functions {
unsigned long ip;
unsigned long parent_ip;
};
static struct recursed_functions recursed_functions[CONFIG_FTRACE_RECORD_RECURSION_SIZE];
static atomic_t nr_records;
/*
* Cache the last found function. Yes, updates to this is racey, but
* so is memory cache ;-)
*/
static unsigned long cached_function;
void ftrace_record_recursion(unsigned long ip, unsigned long parent_ip)
{
int index = 0;
int i;
unsigned long old;
again:
/* First check the last one recorded */
if (ip == cached_function)
return;
i = atomic_read(&nr_records);
/* nr_records is -1 when clearing records */
smp_mb__after_atomic();
if (i < 0)
return;
/*
* If there's two writers and this writer comes in second,
* the cmpxchg() below to update the ip will fail. Then this
* writer will try again. It is possible that index will now
* be greater than nr_records. This is because the writer
* that succeeded has not updated the nr_records yet.
* This writer could keep trying again until the other writer
* updates nr_records. But if the other writer takes an
* interrupt, and that interrupt locks up that CPU, we do
* not want this CPU to lock up due to the recursion protection,
* and have a bug report showing this CPU as the cause of
* locking up the computer. To not lose this record, this
* writer will simply use the next position to update the
* recursed_functions, and it will update the nr_records
* accordingly.
*/
if (index < i)
index = i;
if (index >= CONFIG_FTRACE_RECORD_RECURSION_SIZE)
return;
for (i = index - 1; i >= 0; i--) {
if (recursed_functions[i].ip == ip) {
cached_function = ip;
return;
}
}
cached_function = ip;
/*
* We only want to add a function if it hasn't been added before.
* Add to the current location before incrementing the count.
* If it fails to add, then increment the index (save in i)
* and try again.
*/
old = cmpxchg(&recursed_functions[index].ip, 0, ip);
if (old != 0) {
/* Did something else already added this for us? */
if (old == ip)
return;
/* Try the next location (use i for the next index) */
index++;
goto again;
}
recursed_functions[index].parent_ip = parent_ip;
/*
* It's still possible that we could race with the clearing
* CPU0 CPU1
* ---- ----
* ip = func
* nr_records = -1;
* recursed_functions[0] = 0;
* i = -1
* if (i < 0)
* nr_records = 0;
* (new recursion detected)
* recursed_functions[0] = func
* cmpxchg(recursed_functions[0],
* func, 0)
*
* But the worse that could happen is that we get a zero in
* the recursed_functions array, and it's likely that "func" will
* be recorded again.
*/
i = atomic_read(&nr_records);
smp_mb__after_atomic();
if (i < 0)
cmpxchg(&recursed_functions[index].ip, ip, 0);
else if (i <= index)
atomic_cmpxchg(&nr_records, i, index + 1);
}
EXPORT_SYMBOL_GPL(ftrace_record_recursion);
static DEFINE_MUTEX(recursed_function_lock);
static struct trace_seq *tseq;
static void *recursed_function_seq_start(struct seq_file *m, loff_t *pos)
{
void *ret = NULL;
int index;
mutex_lock(&recursed_function_lock);
index = atomic_read(&nr_records);
if (*pos < index) {
ret = &recursed_functions[*pos];
}
tseq = kzalloc(sizeof(*tseq), GFP_KERNEL);
if (!tseq)
return ERR_PTR(-ENOMEM);
trace_seq_init(tseq);
return ret;
}
static void *recursed_function_seq_next(struct seq_file *m, void *v, loff_t *pos)
{
int index;
int p;
index = atomic_read(&nr_records);
p = ++(*pos);
return p < index ? &recursed_functions[p] : NULL;
}
static void recursed_function_seq_stop(struct seq_file *m, void *v)
{
kfree(tseq);
mutex_unlock(&recursed_function_lock);
}
static int recursed_function_seq_show(struct seq_file *m, void *v)
{
struct recursed_functions *record = v;
int ret = 0;
if (record) {
trace_seq_print_sym(tseq, record->parent_ip, true);
trace_seq_puts(tseq, ":\t");
trace_seq_print_sym(tseq, record->ip, true);
trace_seq_putc(tseq, '\n');
ret = trace_print_seq(m, tseq);
}
return ret;
}
static const struct seq_operations recursed_function_seq_ops = {
.start = recursed_function_seq_start,
.next = recursed_function_seq_next,
.stop = recursed_function_seq_stop,
.show = recursed_function_seq_show
};
static int recursed_function_open(struct inode *inode, struct file *file)
{
int ret = 0;
mutex_lock(&recursed_function_lock);
/* If this file was opened for write, then erase contents */
if ((file->f_mode & FMODE_WRITE) && (file->f_flags & O_TRUNC)) {
/* disable updating records */
atomic_set(&nr_records, -1);
smp_mb__after_atomic();
memset(recursed_functions, 0, sizeof(recursed_functions));
smp_wmb();
/* enable them again */
atomic_set(&nr_records, 0);
}
if (file->f_mode & FMODE_READ)
ret = seq_open(file, &recursed_function_seq_ops);
mutex_unlock(&recursed_function_lock);
return ret;
}
static ssize_t recursed_function_write(struct file *file,
const char __user *buffer,
size_t count, loff_t *ppos)
{
return count;
}
static int recursed_function_release(struct inode *inode, struct file *file)
{
if (file->f_mode & FMODE_READ)
seq_release(inode, file);
return 0;
}
static const struct file_operations recursed_functions_fops = {
.open = recursed_function_open,
.write = recursed_function_write,
.read = seq_read,
.llseek = seq_lseek,
.release = recursed_function_release,
};
__init static int create_recursed_functions(void)
{
struct dentry *dentry;
dentry = trace_create_file("recursed_functions", 0644, NULL, NULL,
&recursed_functions_fops);
if (!dentry)
pr_warn("WARNING: Failed to create recursed_functions\n");
return 0;
}
fs_initcall(create_recursed_functions);