Re: [PATCH] stop_machine: Mark functions as notrace

From: Guo Ren
Date: Thu Oct 29 2020 - 12:02:40 EST

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On Thu, Oct 29, 2020 at 8:23 AM Atish Patra <atishp@xxxxxxxxxxxxxx> wrote:
>
> On Wed, Oct 28, 2020 at 8:44 AM Guo Ren <guoren@xxxxxxxxxx> wrote:
> >
> > Hi Zong & Atish,
> >
> > In our 2 harts c910 chip, we found:
> >
> > echo function > /sys/kernel/debug/tracing/current_tracer
> > echo function_graph > /sys/kernel/debug/tracing/current_tracer
> > echo function > /sys/kernel/debug/tracing/current_tracer
> > echo function_graph > /sys/kernel/debug/tracing/current_tracer
> >
> > Then one core halted at stop_machine_yield:
> > arch_cpu_idle () at arch/riscv/kernel/process.c:39
> > 39 local_irq_enable();
> > (gdb) i th
> > Id Target Id Frame
> > * 1 Thread 1 (CPU#0) arch_cpu_idle () at arch/riscv/kernel/process.c:39
> > 2 Thread 2 (CPU#1) stop_machine_yield
> > (cpumask=0xffffffe001371fa8 <__cpu_online_mask>) at
> > ./arch/riscv/include/asm/vdso/processor.h:12
> > (gdb) thread 2
> > [Switching to thread 2 (Thread 2)]
> > #0 stop_machine_yield (cpumask=0xffffffe001371fa8
> > <__cpu_online_mask>) at ./arch/riscv/include/asm/vdso/processor.h:12
> > 12 __asm__ __volatile__ ("div %0, %0, zero" : "=r" (dummy));
> >
> > With your patch, it's solved. For this patch, I'll give:
> > Tested by: Guo Ren <guoren@xxxxxxxxxx>
> >
> > But that's not enough, we still need:
> >
> > diff --git a/arch/riscv/kernel/sbi.c b/arch/riscv/kernel/sbi.c
> > index 226ccce..12b8808 100644
> > --- a/arch/riscv/kernel/sbi.c
> > +++ b/arch/riscv/kernel/sbi.c
> > @@ -376,7 +376,7 @@ EXPORT_SYMBOL(sbi_send_ipi);
> > *
> > * Return: None
> > */
> > -void sbi_remote_fence_i(const unsigned long *hart_mask)
> > +void notrace sbi_remote_fence_i(const unsigned long *hart_mask)
> > {
> > __sbi_rfence(SBI_EXT_RFENCE_REMOTE_FENCE_I,
> > hart_mask, 0, 0, 0, 0);
> > diff --git a/arch/riscv/mm/cacheflush.c b/arch/riscv/mm/cacheflush.c
> > index 400b945d..9467d987 100644
> > --- a/arch/riscv/mm/cacheflush.c
> > +++ b/arch/riscv/mm/cacheflush.c
> > @@ -9,12 +9,12 @@
> >
> > #include <asm/sbi.h>
> >
> > -static void ipi_remote_fence_i(void *info)
> > +static void notrace ipi_remote_fence_i(void *info)
> > {
> > return local_flush_icache_all();
> > }
> >
> > -void flush_icache_all(void)
> > +void notrace flush_icache_all(void)
> > {
> > if (IS_ENABLED(CONFIG_RISCV_SBI))
> > sbi_remote_fence_i(NULL);
> >
>
> Did you see any issue if these functions are not marked as notrace ?

Welcome to Buildroot
buildroot login: root
#
# cat /proc/cpuinfo
processor : 0
hart : 0
isa : rv64imafdcsu
mmu : sv39
#
#
# echo function > /sys/kernel/debug/tracing/current_tracer
[ 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
#5 0xffffffe0002c9c04 in __ftrace_replace_code
(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 !

Look when we modify flush_icache_all's patchable-entry with ftrace_caller:
1. Insert ftrace_caller at flush_icache_all entry.
2. Call flush_icache_all to sync I/Dcache, but flush_icache_all is
just we've modified not ready to be called!

>
> As per Zong's explanation, the issue was that the other harts already
> fetched the next 2 nops and
> executed 1 while kernel patching replaced other with one of the auipc
> + jalr pair.
>
> @Zong can correct me if I am wrong.
>
> These functions are too far ahead. Can it cause such issues ? If yes,
> then we need to mark each and every function
> that can be invoked from patch_text_nosync and are not inlined.
>
> That includes copy_to_kernel_nofault, __sbi_rfence_v02,
> __sbi_rfence_v02_call, sbi_ecall.
Yes, mark all of them.

>
> Few of these functions may be inlined by compiler. Can we depend on that ?
It works, but we'd better give notrace for them.

>
> > Because:
> > (gdb) bt
> > #0 flush_icache_all () at arch/riscv/mm/cacheflush.c:20
> > #1 0xffffffe00020473a in patch_text_nosync (addr=<optimized out>, insns=
> > <optimized out>, len=<optimized out>) at arch/riscv/kernel/patch.c:96
> > #2 0xffffffe000206792 in ftrace_make_call (rec=<optimized out>,
> > addr=<optimized out>) at arch/riscv/kernel/ftrace.c:109
> > #3 0xffffffe0002c9be4 in __ftrace_replace_code (rec=0xffffffe01ae40020, e
> > nable=true) at kernel/trace/ftrace.c:2503
> > #4 0xffffffe0002ca092 in ftrace_replace_code (mod_flags=<optimized
> > out>) at kernel/trace/ftrace.c:2530
> > #5 0xffffffe0002ca24a in ftrace_modify_all_code (command=9) at kernel
> > /trace/ftrace.c:2677
> > #6 0xffffffe0002ca2ee in __ftrace_modify_code (data=<optimized out>) at
> > kernel/trace/ftrace.c:2703
> > #7 0xffffffe0002c1390 in multi_cpu_stop (data=0x0) at kernel/stop_machin
> > e.c:224
> > #8 0xffffffe0002c0fbe in cpu_stopper_thread (cpu=<optimized out>) at kern
> > el/stop_machine.c:491
> > #9 0xffffffe0002343be in smpboot_thread_fn (data=0x0) at kernel/smpboot.
> > c:165
> > #10 0xffffffe00022f894 in kthread (_create=0xffffffe01af13040) at kern
> > el/kthread.c:292
> > #11 0xffffffe000201fac in handle_exception () at arch/riscv/kernel/entry.S:236
> >
> > On Wed, Oct 21, 2020 at 3:38 PM Zong Li <zong.li@xxxxxxxxxx> wrote:
> > >
> > > Like the commit cb9d7fd51d9f ("watchdog: Mark watchdog touch functions
> > > as notrace"), some architectures assume that the stopped CPUs don't make
> > > function calls to traceable functions when they are in the stopped
> > > state. For example, it causes unexpected kernel crashed when switching
> > > tracer on RISC-V.
> > >
> > > The following patches added calls to these two functions, fix it by
> > > adding the notrace annotations.
> > >
> > > Fixes: 4ecf0a43e729 ("processor: get rid of cpu_relax_yield")
> > > Fixes: 366237e7b083 ("stop_machine: Provide RCU quiescent state in
> > > multi_cpu_stop()")
> > >
> > > Signed-off-by: Zong Li <zong.li@xxxxxxxxxx>
> > > ---
> > > kernel/rcu/tree.c | 2 +-
> > > kernel/stop_machine.c | 2 +-
> > > 2 files changed, 2 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> > > index 06895ef85d69..2a52f42f64b6 100644
> > > --- a/kernel/rcu/tree.c
> > > +++ b/kernel/rcu/tree.c
> > > @@ -409,7 +409,7 @@ bool rcu_eqs_special_set(int cpu)
> > > *
> > > * The caller must have disabled interrupts and must not be idle.
> > > */
> > > -void rcu_momentary_dyntick_idle(void)
> > > +notrace void rcu_momentary_dyntick_idle(void)
> > > {
> > > int special;
> > >
> > > diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c
> > > index 865bb0228ab6..890b79cf0e7c 100644
> > > --- a/kernel/stop_machine.c
> > > +++ b/kernel/stop_machine.c
> > > @@ -178,7 +178,7 @@ static void ack_state(struct multi_stop_data *msdata)
> > > set_state(msdata, msdata->state + 1);
> > > }
> > >
> > > -void __weak stop_machine_yield(const struct cpumask *cpumask)
> > > +notrace void __weak stop_machine_yield(const struct cpumask *cpumask)
> > > {
> > > cpu_relax();
> > > }
> > > --
> > > 2.28.0
> > >
> >
> >
> > --
> > Best Regards
> > Guo Ren
> >
> > ML: https://lore.kernel.org/linux-csky/
>
>
>
> --
> Regards,
> Atish

--
Best Regards
Guo Ren

ML: https://lore.kernel.org/linux-csky/

Next message: Uros Bizjak: "[PATCH v2] x86/boot/64: Use TEST %reg,%reg instead of CMP $0,%reg"
Previous message: Shakeel Butt: "Re: [PATCH v2] mm: memcontrol: Simplify the mem_cgroup_page_lruvec"
In reply to: Guo Ren: "Re: [PATCH] stop_machine: Mark functions as notrace"
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