[for-next][PATCH 01/12] ftrace: show debugging information when panic_on_warn set

[Steven Rostedt]

From: Cheng Jian <cj.chengj...@huawei.com>

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

Link: https://lkml.kernel.org/r/20200515100828.7091-1-cj.chengj...@huawei.com

Signed-off-by: Cheng Jian <cj.chengj...@huawei.com>
Signed-off-by: Steven Rostedt (VMware) <rost...@goodmis.org>
---
 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)
-- 
2.26.2