[PATCH] ftrace: show debugging information when panic_on_warn set

From: Cheng Jian
Date: Fri May 15 2020 - 06:08:40 EST


When an anomaly is detected in the function call modification
code, ftrace_bug() is called to disable function tracing as well
as give some warn and information that may help debug the problem.

But currently, we call FTRACE_WARN_ON_ONCE() first in ftrace_bug(),
so when panic_on_warn is set, we can't see the debugging information
here. Call FTRACE_WARN_ON_ONCE() at the end of ftrace_bug() to ensure
that the debugging information is displayed first.

after this patch, the dmesg looks like:

------------[ ftrace bug ]------------
ftrace failed to modify
[<ffff800010081004>] bcm2835_handle_irq+0x4/0x58
actual: 1f:20:03:d5
Setting ftrace call site to call ftrace function
ftrace record flags: 80000001
(1)
expected tramp: ffff80001009d6f0
------------[ cut here ]------------
WARNING: CPU: 2 PID: 1635 at kernel/trace/ftrace.c:2078 ftrace_bug+0x204/0x238
Kernel panic - not syncing: panic_on_warn set ...
CPU: 2 PID: 1635 Comm: sh Not tainted 5.7.0-rc5-00033-gb922183867f5 #14
Hardware name: linux,dummy-virt (DT)
Call trace:
dump_backtrace+0x0/0x1b0
show_stack+0x20/0x30
dump_stack+0xc0/0x10c
panic+0x16c/0x368
__warn+0x120/0x160
report_bug+0xc8/0x160
bug_handler+0x28/0x98
brk_handler+0x70/0xd0
do_debug_exception+0xcc/0x1ac
el1_sync_handler+0xe4/0x120
el1_sync+0x7c/0x100
ftrace_bug+0x204/0x238

Signed-off-by: Cheng Jian <cj.chengjian@xxxxxxxxxx>
---
kernel/trace/ftrace.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index bd030b1b9514..cd39cbf3631a 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -2027,14 +2027,14 @@ void ftrace_bug(int failed, struct dyn_ftrace *rec)
{
unsigned long ip = rec ? rec->ip : 0;

+ pr_info("------------[ ftrace bug ]------------\n");
+
switch (failed) {
case -EFAULT:
- FTRACE_WARN_ON_ONCE(1);
pr_info("ftrace faulted on modifying ");
print_ip_sym(ip);
break;
case -EINVAL:
- FTRACE_WARN_ON_ONCE(1);
pr_info("ftrace failed to modify ");
print_ip_sym(ip);
print_ip_ins(" actual: ", (unsigned char *)ip);
@@ -2045,12 +2045,10 @@ void ftrace_bug(int failed, struct dyn_ftrace *rec)
}
break;
case -EPERM:
- FTRACE_WARN_ON_ONCE(1);
pr_info("ftrace faulted on writing ");
print_ip_sym(ip);
break;
default:
- FTRACE_WARN_ON_ONCE(1);
pr_info("ftrace faulted on unknown error ");
print_ip_sym(ip);
}
@@ -2077,6 +2075,8 @@ void ftrace_bug(int failed, struct dyn_ftrace *rec)
ip = ftrace_get_addr_curr(rec);
pr_cont("\n expected tramp: %lx\n", ip);
}
+
+ FTRACE_WARN_ON_ONCE(1);
}

static int ftrace_check_record(struct dyn_ftrace *rec, bool enable, bool update)
--
2.17.1