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Subject[RFC PATCH] riscv: stacktrace: fix the riscv stacktrace when CONFIG_FRAME_POINTER enabled
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As [1] and [2] said, the arch_stack_walk should not to trace itself, or it will
leave the trace unexpectedly when called. The example is when we do "cat
/sys/kernel/debug/page_owner", all pages' stack is the same.

arch_stack_walk+0x18/0x20
stack_trace_save+0x40/0x60
register_dummy_stack+0x24/0x5e
init_page_owner+0x2e

So we use __builtin_frame_address(1) as the first frame to be walked. And mark
the arch_stack_walk() noinline.

We found that pr_cont will affact pages' stack whose task state is RUNNING when
testing "echo t > /proc/sysrq-trigger". So move the place of pr_cont and mark
the function dump_backtrace() noinline.

Also we move the case when task == NULL into else branch, and test for it in
"echo c > /proc/sysrq-trigger".

[1] https://lore.kernel.org/lkml/20210319184106.5688-1-mark.rutland@arm.com/
[2] https://lore.kernel.org/lkml/20210317142050.57712-1-chenjun102@huawei.com/

Signed-off-by: Chen Huang <chenhuang5@huawei.com>
---
In this way, some crash will loss the print info "Call trace:", likes that:
# echo BUG > /sys/kernel/debug/provoke-crash/DIRECT
[ 61.774690] lkdtm: Performing direct entry BUG
[ 61.775350] ------------[ cut here ]------------
[ 61.775611] kernel BUG at drivers/misc/lkdtm/bugs.c:76!
[ 61.776073] Kernel BUG [#1]
[ 61.776319] Modules linked in:
[ 61.776696] CPU: 3 PID: 1 Comm: sh Not tainted 5.11.0-rc6-next-20210208-00013-gb16da2c3b9aa #132
[ 61.777185] Hardware name: riscv-virtio,qemu (DT)
[ 61.777594] epc : lkdtm_BUG+0x6/0x8
[ 61.777916] ra : lkdtm_do_action+0x14/0x1c
[ 61.778212] epc : ffffffe00048a7e8 ra : ffffffe0006d71a8 sp : ffffffe07fedbd90
[ 61.778646] gp : ffffffe0012e4208 tp : ffffffe07fed0000 t0 : ffffffe0012f2097
[ 61.779115] t1 : ffffffe0012f2088 t2 : 0000000000000000 s0 : ffffffe07fedbda0
[ 61.779588] s1 : 0000000000000010 a0 : ffffffe000c7fbb8 a1 : ffffffe001284d28
[ 61.780017] a2 : 0000000000000010 a3 : 0000000000000000 a4 : c10724222fbe9200
[ 61.780473] a5 : ffffffe00048a7e2 a6 : c0000000ffffefff a7 : 0000000000000064
[ 61.780932] s2 : ffffffe000c7fbc8 s3 : ffffffe000d9e3f8 s4 : ffffffe081969000
[ 61.781405] s5 : 000000000000004b s6 : 0000000000000004 s7 : ffffffe07fedbe80
[ 61.781872] s8 : 0000003ffff987e4 s9 : 0000002ab0b7ac50 s10: 0000002ab0bacb90
[ 61.782336] s11: 0000000000000000 t3 : 000000000000006c t4 : ffffffffffffffff
[ 61.782794] t5 : 0000000000000037 t6 : ffffffe07fedbae8
[ 61.783158] status: 0000000000000120 badaddr: 0000000000000000 cause: 0000000000000003
[ 61.783680] [<ffffffe00048a7e8>] lkdtm_BUG+0x6/0x8
[ 61.784149] [<ffffffe0006d71a8>] lkdtm_do_action+0x14/0x1c
[ 61.784516] [<ffffffe00048a5ee>] direct_entry+0xc0/0x10a
[ 61.784849] [<ffffffe0002498ce>] full_proxy_write+0x42/0x6a
[ 61.785209] [<ffffffe000114b7c>] vfs_write+0x7e/0x218
[ 61.785562] [<ffffffe000114e84>] ksys_write+0x98/0xc0
[ 61.785904] [<ffffffe000114eba>] sys_write+0xe/0x16
[ 61.786275] [<ffffffe000003466>] ret_from_syscall+0x0/0x2
[ 61.787175] ---[ end trace 6919e7283b64f492 ]---
[ 61.787707] Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b
[ 61.788270] SMP: stopping secondary CPUs
[ 61.788934] ---[ end Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b ]---

arch/riscv/kernel/stacktrace.c | 14 +++++++-------
1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/arch/riscv/kernel/stacktrace.c b/arch/riscv/kernel/stacktrace.c
index 2b3e0cb90d78..bde85fc53357 100644
--- a/arch/riscv/kernel/stacktrace.c
+++ b/arch/riscv/kernel/stacktrace.c
@@ -27,10 +27,10 @@ void notrace walk_stackframe(struct task_struct *task, struct pt_regs *regs,
fp = frame_pointer(regs);
sp = user_stack_pointer(regs);
pc = instruction_pointer(regs);
- } else if (task == NULL || task == current) {
- fp = (unsigned long)__builtin_frame_address(0);
- sp = sp_in_global;
- pc = (unsigned long)walk_stackframe;
+ } else if (task == current) {
+ fp = (unsigned long)__builtin_frame_address(1);
+ sp = (unsigned long)__builtin_frame_address(0);
+ pc = (unsigned long)__builtin_return_address(0);
} else {
/* task blocked in __switch_to */
fp = task->thread.s[0];
@@ -106,15 +106,15 @@ static bool print_trace_address(void *arg, unsigned long pc)
return true;
}

-void dump_backtrace(struct pt_regs *regs, struct task_struct *task,
+noinline void dump_backtrace(struct pt_regs *regs, struct task_struct *task,
const char *loglvl)
{
- pr_cont("%sCall Trace:\n", loglvl);
walk_stackframe(task, regs, print_trace_address, (void *)loglvl);
}

void show_stack(struct task_struct *task, unsigned long *sp, const char *loglvl)
{
+ pr_cont("%sCall Trace:\n", loglvl);
dump_backtrace(NULL, task, loglvl);
}

@@ -139,7 +139,7 @@ unsigned long get_wchan(struct task_struct *task)

#ifdef CONFIG_STACKTRACE

-void arch_stack_walk(stack_trace_consume_fn consume_entry, void *cookie,
+noinline void arch_stack_walk(stack_trace_consume_fn consume_entry, void *cookie,
struct task_struct *task, struct pt_regs *regs)
{
walk_stackframe(task, regs, consume_entry, cookie);
--
2.17.1
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