[PATCH v5 4/9] riscv: Fixup patch_text panic in ftrace

From: guoren
Date: Thu Dec 17 2020 - 11:05:06 EST

From: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>

Just like arm64, we can't trace the function in the patch_text path.

Here is the bug log:

[ 45.234334] Unable to handle kernel paging request at virtual address ffffffd38ae80900
[ 45.242313] Oops [#1]
[ 45.244600] Modules linked in:
[ 45.247678] CPU: 0 PID: 11 Comm: migration/0 Not tainted 5.9.0-00025-g9b7db83-dirty #215
[ 45.255797] epc: ffffffe00021689a ra : ffffffe00021718e sp : ffffffe01afabb58
[ 45.262955] gp : ffffffe00136afa0 tp : ffffffe01af94d00 t0 : 0000000000000002
[ 45.270200] t1 : 0000000000000000 t2 : 0000000000000001 s0 : ffffffe01afabc08
[ 45.277443] s1 : ffffffe0013718a8 a0 : 0000000000000000 a1 : ffffffe01afabba8
[ 45.284686] a2 : 0000000000000000 a3 : 0000000000000000 a4 : c4c16ad38ae80900
[ 45.291929] a5 : 0000000000000000 a6 : 0000000000000000 a7 : 0000000052464e43
[ 45.299173] s2 : 0000000000000001 s3 : ffffffe000206a60 s4 : ffffffe000206a60
[ 45.306415] s5 : 00000000000009ec s6 : ffffffe0013718a8 s7 : c4c16ad38ae80900
[ 45.313658] s8 : 0000000000000004 s9 : 0000000000000001 s10: 0000000000000001
[ 45.320902] s11: 0000000000000003 t3 : 0000000000000001 t4 : ffffffffd192fe79
[ 45.328144] t5 : ffffffffb8f80000 t6 : 0000000000040000
[ 45.333472] status: 0000000200000100 badaddr: ffffffd38ae80900 cause: 000000000000000f
[ 45.341514] ---[ end trace d95102172248fdcf ]---
[ 45.346176] note: migration/0[11] exited with preempt_count 1

(gdb) x /2i $pc
=> 0xffffffe00021689a <__do_proc_dointvec+196>: sd zero,0(s7)
0xffffffe00021689e <__do_proc_dointvec+200>: li s11,0

(gdb) bt
0 __do_proc_dointvec (tbl_data=0x0, table=0xffffffe01afabba8,
write=0, buffer=0x0, lenp=0x7bf897061f9a0800, ppos=0x4, conv=0x0,
data=0x52464e43) at kernel/sysctl.c:581
1 0xffffffe00021718e in do_proc_dointvec (data=<optimized out>,
conv=<optimized out>, ppos=<optimized out>, lenp=<optimized out>,
buffer=<optimized out>, write=<optimized out>, table=<optimized out>)
at kernel/sysctl.c:964
2 proc_dointvec_minmax (ppos=<optimized out>, lenp=<optimized out>,
buffer=<optimized out>, write=<optimized out>, table=<optimized out>)
at kernel/sysctl.c:964
3 proc_do_static_key (table=<optimized out>, write=1, buffer=0x0,
lenp=0x0, ppos=0x7bf897061f9a0800) at kernel/sysctl.c:1643
4 0xffffffe000206792 in ftrace_make_call (rec=<optimized out>,
addr=<optimized out>) at arch/riscv/kernel/ftrace.c:109
5 0xffffffe0002c9c04 in __ftrace_replace_code
(rec=0xffffffe01ae40c30, enable=3) at kernel/trace/ftrace.c:2503
6 0xffffffe0002ca0b2 in ftrace_replace_code (mod_flags=<optimized
out>) at kernel/trace/ftrace.c:2530
7 0xffffffe0002ca26a in ftrace_modify_all_code (command=5) at
kernel/trace/ftrace.c:2677
8 0xffffffe0002ca30e in __ftrace_modify_code (data=<optimized out>)
at kernel/trace/ftrace.c:2703
9 0xffffffe0002c13b0 in multi_cpu_stop (data=0x0) at kernel/stop_machine.c:224
10 0xffffffe0002c0fde in cpu_stopper_thread (cpu=<optimized out>) at
kernel/stop_machine.c:491
11 0xffffffe0002343de in smpboot_thread_fn (data=0x0) at kernel/smpboot.c:165
12 0xffffffe00022f8b4 in kthread (_create=0xffffffe01af0c040) at
kernel/kthread.c:292
13 0xffffffe000201fac in handle_exception () at arch/riscv/kernel/entry.S:236

0xffffffe00020678a <+114>: auipc ra,0xffffe
0xffffffe00020678e <+118>: jalr -118(ra) # 0xffffffe000204714 <patch_text_nosync>
0xffffffe000206792 <+122>: snez a0,a0

(gdb) disassemble patch_text_nosync
Dump of assembler code for function patch_text_nosync:
0xffffffe000204714 <+0>: addi sp,sp,-32
0xffffffe000204716 <+2>: sd s0,16(sp)
0xffffffe000204718 <+4>: sd ra,24(sp)
0xffffffe00020471a <+6>: addi s0,sp,32
0xffffffe00020471c <+8>: auipc ra,0x0
0xffffffe000204720 <+12>: jalr -384(ra) # 0xffffffe00020459c <patch_insn_write>
0xffffffe000204724 <+16>: beqz a0,0xffffffe00020472e <patch_text_nosync+26>
0xffffffe000204726 <+18>: ld ra,24(sp)
0xffffffe000204728 <+20>: ld s0,16(sp)
0xffffffe00020472a <+22>: addi sp,sp,32
0xffffffe00020472c <+24>: ret
0xffffffe00020472e <+26>: sd a0,-24(s0)
0xffffffe000204732 <+30>: auipc ra,0x4
0xffffffe000204736 <+34>: jalr -1464(ra) # 0xffffffe00020817a <flush_icache_all>
0xffffffe00020473a <+38>: ld a0,-24(s0)
0xffffffe00020473e <+42>: ld ra,24(sp)
0xffffffe000204740 <+44>: ld s0,16(sp)
0xffffffe000204742 <+46>: addi sp,sp,32
0xffffffe000204744 <+48>: ret

(gdb) disassemble flush_icache_all-4
Dump of assembler code for function flush_icache_all:
0xffffffe00020817a <+0>: addi sp,sp,-8
0xffffffe00020817c <+2>: sd ra,0(sp)
0xffffffe00020817e <+4>: auipc ra,0xfffff
0xffffffe000208182 <+8>: jalr -1822(ra) # 0xffffffe000206a60 <ftrace_caller>
0xffffffe000208186 <+12>: ld ra,0(sp)
0xffffffe000208188 <+14>: addi sp,sp,8
0xffffffe00020818a <+0>: addi sp,sp,-16
0xffffffe00020818c <+2>: sd s0,0(sp)
0xffffffe00020818e <+4>: sd ra,8(sp)
0xffffffe000208190 <+6>: addi s0,sp,16
0xffffffe000208192 <+8>: li a0,0
0xffffffe000208194 <+10>: auipc ra,0xfffff
0xffffffe000208198 <+14>: jalr -410(ra) # 0xffffffe000206ffa <sbi_remote_fence_i>
0xffffffe00020819c <+18>: ld s0,0(sp)
0xffffffe00020819e <+20>: ld ra,8(sp)
0xffffffe0002081a0 <+22>: addi sp,sp,16
0xffffffe0002081a2 <+24>: ret

(gdb) frame 5
(rec=0xffffffe01ae40c30, enable=3) at kernel/trace/ftrace.c:2503
2503 return ftrace_make_call(rec, ftrace_addr);
(gdb) p /x rec->ip
$2 = 0xffffffe00020817a -> flush_icache_all !

When we modified flush_icache_all's patchable-entry with ftrace_caller:
- Insert ftrace_caller at flush_icache_all prologue.
- Call flush_icache_all to sync I/Dcache, but flush_icache_all is
just we modified by half.

Link: https://lore.kernel.org/linux-riscv/CAJF2gTT=oDWesWe0JVWvTpGi60-gpbNhYLdFWN_5EbyeqoEDdw@xxxxxxxxxxxxxx/T/#t
Signed-off-by: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>
Cc: Atish Patra <atish.patra@xxxxxxx>
Cc: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
---
arch/riscv/kernel/Makefile | 1 +
arch/riscv/mm/Makefile | 1 +
2 files changed, 2 insertions(+)

diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile
index 27f10eb..62de075 100644
--- a/arch/riscv/kernel/Makefile
+++ b/arch/riscv/kernel/Makefile
@@ -6,6 +6,7 @@
ifdef CONFIG_FTRACE
CFLAGS_REMOVE_ftrace.o = $(CC_FLAGS_FTRACE)
CFLAGS_REMOVE_patch.o = $(CC_FLAGS_FTRACE)
+CFLAGS_REMOVE_sbi.o = $(CC_FLAGS_FTRACE)
endif

extra-y += head.o
diff --git a/arch/riscv/mm/Makefile b/arch/riscv/mm/Makefile
index 6b4b7ec..7ebaef1 100644
--- a/arch/riscv/mm/Makefile
+++ b/arch/riscv/mm/Makefile
@@ -3,6 +3,7 @@
CFLAGS_init.o := -mcmodel=medany
ifdef CONFIG_FTRACE
CFLAGS_REMOVE_init.o = $(CC_FLAGS_FTRACE)
+CFLAGS_REMOVE_cacheflush.o = $(CC_FLAGS_FTRACE)
endif

KCOV_INSTRUMENT_init.o := n
--
2.7.4