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Date:   Thu, 3 Jun 2021 19:54:18 +0800
From:   Jisheng Zhang <jszhang3@mail.ustc.edu.cn>
To:     Nathan Chancellor <nathan@kernel.org>
Cc:     Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        Alexandre Ghiti <alex@ghiti.fr>,
        linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org,
        clang-built-linux@googlegroups.com
Subject: Re: [PATCH] riscv: mm: init: Consolidate vars, functions
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On Thu, 3 Jun 2021 08:27:14 +0800
Jisheng Zhang <jszhang3@mail.ustc.edu.cn> wrote:

> On Wed, 2 Jun 2021 12:54:40 -0700
> Nathan Chancellor <nathan@kernel.org> wrote:
> 
> > On Wed, Jun 02, 2021 at 11:58:51PM +0800, Jisheng Zhang wrote:  
> > > On Wed, 2 Jun 2021 23:12:26 +0800
> > > Jisheng Zhang <jszhang3@mail.ustc.edu.cn> wrote:
> > >     
> > > > On Tue, 1 Jun 2021 13:21:05 -0700
> > > > Nathan Chancellor <nathan@kernel.org> wrote:
> > > >     
> > > > > Hi Jisheng,      
> > > > 
> > > > Hi Nathan,
> > > >     
> > > > > 
> > > > > On Sun, May 16, 2021 at 09:15:56PM +0800, Jisheng Zhang wrote:      
> > > > > > From: Jisheng Zhang <jszhang@kernel.org>
> > > > > > 
> > > > > > Consolidate the following items in init.c
> > > > > > 
> > > > > > Staticize global vars as much as possible;
> > > > > > Add __initdata mark if the global var isn't needed after init
> > > > > > Add __init mark if the func isn't needed after init
> > > > > > Add __ro_after_init if the global var is read only after init
> > > > > > 
> > > > > > Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
> > > > > > ---
> > > > > >  arch/riscv/include/asm/set_memory.h |  2 +-
> > > > > >  arch/riscv/mm/init.c                | 36 +++++++++++++++--------------
> > > > > >  2 files changed, 20 insertions(+), 18 deletions(-)
> > > > > > 
> > > > > > diff --git a/arch/riscv/include/asm/set_memory.h b/arch/riscv/include/asm/set_memory.h
> > > > > > index 086f757e8ba3..9d4d455726d4 100644
> > > > > > --- a/arch/riscv/include/asm/set_memory.h
> > > > > > +++ b/arch/riscv/include/asm/set_memory.h
> > > > > > @@ -27,7 +27,7 @@ static inline int set_memory_rw_nx(unsigned long addr, int numpages) { return 0;
> > > > > >  #endif
> > > > > >  
> > > > > >  #if defined(CONFIG_64BIT) && defined(CONFIG_STRICT_KERNEL_RWX)
> > > > > > -void protect_kernel_linear_mapping_text_rodata(void);
> > > > > > +void __init protect_kernel_linear_mapping_text_rodata(void);
> > > > > >  #else
> > > > > >  static inline void protect_kernel_linear_mapping_text_rodata(void) {}
> > > > > >  #endif
> > > > > > diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> > > > > > index 4c4c92ce0bb8..eac2d5c27b3e 100644
> > > > > > --- a/arch/riscv/mm/init.c
> > > > > > +++ b/arch/riscv/mm/init.c
> > > > > > @@ -53,7 +53,7 @@ struct pt_alloc_ops {
> > > > > >  #endif
> > > > > >  };
> > > > > >  
> > > > > > -static phys_addr_t dma32_phys_limit __ro_after_init;
> > > > > > +static phys_addr_t dma32_phys_limit __initdata;
> > > > > >  
> > > > > >  static void __init zone_sizes_init(void)
> > > > > >  {
> > > > > > @@ -184,7 +184,7 @@ extern char _sdata[], _edata[];
> > > > > >  #endif /* CONFIG_XIP_KERNEL */
> > > > > >  
> > > > > >  #ifdef CONFIG_MMU
> > > > > > -static struct pt_alloc_ops _pt_ops __ro_after_init;
> > > > > > +static struct pt_alloc_ops _pt_ops __initdata;
> > > > > >  
> > > > > >  #ifdef CONFIG_XIP_KERNEL
> > > > > >  #define pt_ops (*(struct pt_alloc_ops *)XIP_FIXUP(&_pt_ops))
> > > > > > @@ -200,13 +200,13 @@ EXPORT_SYMBOL(va_pa_offset);
> > > > > >  #endif
> > > > > >  /* Offset between kernel mapping virtual address and kernel load address */
> > > > > >  #ifdef CONFIG_64BIT
> > > > > > -unsigned long va_kernel_pa_offset;
> > > > > > +unsigned long va_kernel_pa_offset __ro_after_init;
> > > > > >  EXPORT_SYMBOL(va_kernel_pa_offset);
> > > > > >  #endif
> > > > > >  #ifdef CONFIG_XIP_KERNEL
> > > > > >  #define va_kernel_pa_offset    (*((unsigned long *)XIP_FIXUP(&va_kernel_pa_offset)))
> > > > > >  #endif
> > > > > > -unsigned long va_kernel_xip_pa_offset;
> > > > > > +unsigned long va_kernel_xip_pa_offset __ro_after_init;
> > > > > >  EXPORT_SYMBOL(va_kernel_xip_pa_offset);
> > > > > >  #ifdef CONFIG_XIP_KERNEL
> > > > > >  #define va_kernel_xip_pa_offset        (*((unsigned long *)XIP_FIXUP(&va_kernel_xip_pa_offset)))
> > > > > > @@ -216,7 +216,7 @@ EXPORT_SYMBOL(pfn_base);
> > > > > >  
> > > > > >  pgd_t swapper_pg_dir[PTRS_PER_PGD] __page_aligned_bss;
> > > > > >  pgd_t trampoline_pg_dir[PTRS_PER_PGD] __page_aligned_bss;
> > > > > > -pte_t fixmap_pte[PTRS_PER_PTE] __page_aligned_bss;
> > > > > > +static pte_t fixmap_pte[PTRS_PER_PTE] __page_aligned_bss;
> > > > > >  
> > > > > >  pgd_t early_pg_dir[PTRS_PER_PGD] __initdata __aligned(PAGE_SIZE);
> > > > > >  
> > > > > > @@ -253,7 +253,7 @@ static inline pte_t *__init get_pte_virt_fixmap(phys_addr_t pa)
> > > > > >  	return (pte_t *)set_fixmap_offset(FIX_PTE, pa);
> > > > > >  }
> > > > > >  
> > > > > > -static inline pte_t *get_pte_virt_late(phys_addr_t pa)
> > > > > > +static inline pte_t *__init get_pte_virt_late(phys_addr_t pa)
> > > > > >  {
> > > > > >  	return (pte_t *) __va(pa);
> > > > > >  }
> > > > > > @@ -272,7 +272,7 @@ static inline phys_addr_t __init alloc_pte_fixmap(uintptr_t va)
> > > > > >  	return memblock_phys_alloc(PAGE_SIZE, PAGE_SIZE);
> > > > > >  }
> > > > > >  
> > > > > > -static phys_addr_t alloc_pte_late(uintptr_t va)
> > > > > > +static phys_addr_t __init alloc_pte_late(uintptr_t va)
> > > > > >  {
> > > > > >  	unsigned long vaddr;
> > > > > >  
> > > > > > @@ -296,10 +296,10 @@ static void __init create_pte_mapping(pte_t *ptep,
> > > > > >  
> > > > > >  #ifndef __PAGETABLE_PMD_FOLDED
> > > > > >  
> > > > > > -pmd_t trampoline_pmd[PTRS_PER_PMD] __page_aligned_bss;
> > > > > > -pmd_t fixmap_pmd[PTRS_PER_PMD] __page_aligned_bss;
> > > > > > -pmd_t early_pmd[PTRS_PER_PMD] __initdata __aligned(PAGE_SIZE);
> > > > > > -pmd_t early_dtb_pmd[PTRS_PER_PMD] __initdata __aligned(PAGE_SIZE);
> > > > > > +static pmd_t trampoline_pmd[PTRS_PER_PMD] __page_aligned_bss;
> > > > > > +static pmd_t fixmap_pmd[PTRS_PER_PMD] __page_aligned_bss;
> > > > > > +static pmd_t early_pmd[PTRS_PER_PMD] __initdata __aligned(PAGE_SIZE);
> > > > > > +static pmd_t early_dtb_pmd[PTRS_PER_PMD] __initdata __aligned(PAGE_SIZE);
> > > > > >  
> > > > > >  #ifdef CONFIG_XIP_KERNEL
> > > > > >  #define trampoline_pmd ((pmd_t *)XIP_FIXUP(trampoline_pmd))
> > > > > > @@ -319,7 +319,7 @@ static pmd_t *__init get_pmd_virt_fixmap(phys_addr_t pa)
> > > > > >  	return (pmd_t *)set_fixmap_offset(FIX_PMD, pa);
> > > > > >  }
> > > > > >  
> > > > > > -static pmd_t *get_pmd_virt_late(phys_addr_t pa)
> > > > > > +static pmd_t *__init get_pmd_virt_late(phys_addr_t pa)
> > > > > >  {
> > > > > >  	return (pmd_t *) __va(pa);
> > > > > >  }
> > > > > > @@ -336,7 +336,7 @@ static phys_addr_t __init alloc_pmd_fixmap(uintptr_t va)
> > > > > >  	return memblock_phys_alloc(PAGE_SIZE, PAGE_SIZE);
> > > > > >  }
> > > > > >  
> > > > > > -static phys_addr_t alloc_pmd_late(uintptr_t va)
> > > > > > +static phys_addr_t __init alloc_pmd_late(uintptr_t va)
> > > > > >  {
> > > > > >  	unsigned long vaddr;
> > > > > >  
> > > > > > @@ -454,14 +454,16 @@ asmlinkage void __init __copy_data(void)
> > > > > >  #error "setup_vm() is called from head.S before relocate so it should not use absolute addressing."
> > > > > >  #endif
> > > > > >  
> > > > > > -uintptr_t load_pa, load_sz;
> > > > > > +static uintptr_t load_pa __initdata;        
> > > > > 
> > > > > Making load_pa static causing clang built kernels to no longer boot,
> > > > > hanging after just a few lines of output in the console:
> > > > > 
> > > > > https://github.com/ClangBuiltLinux/continuous-integration2/runs/2717606254?check_suite_focus=true
> > > > > 
> > > > > I am not sure why that would make a difference nor why GCC is okay with
> > > > > it. If it is a clang bug, it appears to be there for a while, given that
> > > > > it reproduces back to clang-11.      
> > > > 
> > > > I can reproduce the issue. Here are my findindings:
> > > > 
> > > > * gcc + binutils can't reproduce it
> > > > * clang + llvm-utils + ias can reproduce it
> > > > * clang + binutils can reproduce it    
> > 
> > Yes, this seems like something strictly related to clang so that is what
> > I have been testing with.
> >   
> > > > All below tests are done with clang + binutils.
> > > > 
> > > > Then I applied below modification:
> > > > 
> > > > -static uintptr_t load_pa __initdata;
> > > > +uintptr_t load_pa __initdata;
> > > > 
> > > > I got below panic log:
> > > > [    0.015418] Unable to handle kernel paging request at virtual address fffffffffffffff9
> > > > [    0.016432] Oops [#1]
> > > > [    0.016679] Modules linked in:
> > > > [    0.017103] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.13.0-rc1+ #5
> > > > [    0.017711] Hardware name: riscv-virtio,qemu (DT)
> > > > [    0.018201] epc : trace_hardirqs_on+0x60/0xb2
> > > > [    0.018582]  ra : restore_all+0xe/0x66
> > > > [    0.018879] epc : ffffffff800cb09a ra : ffffffff800027b8 sp : ffffffff80c03dd0
> > > > [    0.019376]  gp : ffffffff80d001c8 tp : ffffffff80c0c180 t0 : 0000000000000020
> > > > [    0.019870]  t1 : ffffffff80006e40 t2 : ffffffff800d2e0a s0 : ffffffff80c03e00
> > > > [    0.020346]  s1 : 0000000000000001 a0 : 0000000000000001 a1 : 0000000000000001
> > > > [    0.020800]  a2 : 0000000000000001 a3 : 0000000000000000 a4 : 0000000000000000
> > > > [    0.021243]  a5 : 0000000000000000 a6 : 0000000000000000 a7 : 0000000054494d45
> > > > [    0.021717]  s2 : ffffffff800027b8 s3 : ffffffff80d35968 s4 : ffffffff8061e1d8
> > > > [    0.022179]  s5 : ffffffff80c0c180 s6 : ffffffe000e34b50 s7 : 00000000800130f0
> > > > [    0.022674]  s8 : 000000000000007f s9 : 0000000080012010 s10: 0000000000000000
> > > > [    0.023176]  s11: 0000000000000000 t3 : ffffffff80d00108 t4 : ffffffff80006e40
> > > > [    0.023693]  t5 : ffffffff80006e40 t6 : ffffffff800d2e0a
> > > > [    0.024153] status: 0000000000000100 badaddr: fffffffffffffff9 cause: 000000000000000d
> > > > [    0.025367] Call Trace:
> > > > [    0.025749] [<ffffffff800cb09a>] trace_hardirqs_on+0x60/0xb2
> > > > [    0.026402] [<ffffffff800027b8>] restore_all+0xe/0x66
> > > > [    0.027261] Unable to handle kernel paging request at virtual address fffffffffffffffa
> > > > [    0.027827] Oops [#2]
> > > > [    0.028013] Modules linked in:
> > > > [    0.028321] CPU: 0 PID: 0 Comm: swapper/0 Tainted: G      D           5.13.0-rc1+ #5
> > > > [    0.028839] Hardware name: riscv-virtio,qemu (DT)
> > > > [    0.029166] epc : trace_hardirqs_on+0x60/0xb2
> > > > [    0.029505]  ra : restore_all+0xe/0x66
> > > > [    0.029785] epc : ffffffff800cb09a ra : ffffffff800027b8 sp : ffffffff80c03a80
> > > > [    0.030266]  gp : ffffffff80d001c8 tp : ffffffff80c0c180 t0 : 0000000000000020
> > > > [    0.030748]  t1 : ffffffff80006e40 t2 : ffffffff800d2e0a s0 : ffffffff80c03ab0
> > > > [    0.031227]  s1 : 0000000000000001 a0 : 0000000000000002 a1 : 0000000000000002
> > > > [    0.031717]  a2 : 0000000000000001 a3 : 0000000000000000 a4 : 0000000000000000
> > > > [    0.032199]  a5 : 0000000000000000 a6 : 0000000000000000 a7 : 0000000054494d45
> > > > [    0.032680]  s2 : ffffffff800027b8 s3 : ffffffff80d35968 s4 : ffffffff8061e1d8
> > > > [    0.033160]  s5 : ffffffff80c0c180 s6 : ffffffe000e34b50 s7 : 00000000800130f0
> > > > [    0.033642]  s8 : 000000000000007f s9 : 0000000080012010 s10: 0000000000000000
> > > > [    0.034123]  s11: 0000000000000000 t3 : ffffffff80d00108 t4 : ffffffff80006e40
> > > > [    0.034601]  t5 : ffffffff80006e40 t6 : ffffffff800d2e0a
> > > > [    0.034965] status: 0000000000000100 badaddr: fffffffffffffffa cause: 000000000000000d
> > > > [    0.035492] Call Trace:
> > > > [    0.035682] [<ffffffff800cb09a>] trace_hardirqs_on+0x60/0xb2
> > > > [    0.036077] [<ffffffff800027b8>] restore_all+0xe/0x66
> > > > [    0.036545] ---[ end trace 7f4fbff09d927668 ]---
> > > > [    0.037188] Kernel panic - not syncing: Attempted to kill the idle task!
> > > > [    0.038107] ---[ end Kernel panic - not syncing: Attempted to kill the idle task! ]---
> > > > 
> > > > Then I checked 5.13-rc1, above panic log can be reproduced too. So the issue
> > > > should exist there for a while. I never tried clang with riscv, did you remember
> > > > which last commit or version clang works, I may try to bisect.
> > V> >     
> > > 
> > > More findings:
> > > 
> > > *The above panic issue can also be seen from 5.12-rc2. If disable FTRACE, then
> > > the panic disappears, kernel can boot
> > > 
> > > *so I retested riscv next tree w/ FTRACE disabled, kernel can boot w/ below
> > > modification:    
> > 
> > Yeah, I do not enable CONFIG_FTRACE because it is not enabled in
> > ARCH=riscv defconfig by default.
> >   
> > > -static uintptr_t load_pa __initdata;
> > > +uintptr_t load_pa __initdata;
> > > 
> > > This is a weird issue. Any clue is appreciated.    
> > 
> > Unfortunately, this is outside of my realm of expertise, as I am
> > unfamiliar with RISC-V at this level. Maybe Palmer has some ideas. I
> > would think that changing this variable to static would be fine given
> > that the symbol is only used in this translation unit but clearly not. I
> > have attempted to debug this in gdb but that does not really get me
> > anywhere: I cannot break on start_kernel() for whatever reason and the
> > kernel never gets to my breakpoint in setup_vm().
> > 
> > I did decide to through a BUG() around arch/riscv/mm/init.c to see
> > exactly which statement causes everything to hang. I landed on:
> > 
> > csr_write(CSR_SATP, PFN_DOWN(__pa_symbol(swapper_pg_dir)) | SATP_MODE);
> > 
> > in setup_vm_final(). No idea how that is relevant to this.
> > 
> > Some people in the ClangBuiltLinux bi-weekly meeting today pointed out
> > that since load_pa is assigned to the linker defined symbol _start,
> > there could be some optimization that goes awry here. I have keyed that  
> 
> Thanks for the inspiration. Below patch fixes the hang issue, but I didn't
> go through all necessary WRITE_ONCE convertions.
> 
> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> index ae32f78207f0..fa9336a2583f 100644
> --- a/arch/riscv/mm/init.c
> +++ b/arch/riscv/mm/init.c
> @@ -504,7 +504,7 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
>  
>         va_kernel_xip_pa_offset = kernel_virt_addr - xiprom;
>  #else
> -       load_pa = (uintptr_t)(&_start);
> +       WRITE_ONCE(load_pa, (uintptr_t)(&_start));
>         load_sz = (uintptr_t)(&_end) - load_pa;
>  #endif
> 

I think I found the root cause, but I dunno whether this is clang bug or
we need WRITE_ONCE patch.
W/O WRITE_ONCE, the setup_vm() is compiled to

ffffffff8040472a <setup_vm>:
ffffffff8040472a:       1101                    addi    sp,sp,-32
ffffffff8040472c:       ec06                    sd      ra,24(sp)
ffffffff8040472e:       e822                    sd      s0,16(sp)
ffffffff80404730:       e426                    sd      s1,8(sp)
ffffffff80404732:       e04a                    sd      s2,0(sp)
ffffffff80404734:       1000                    addi    s0,sp,32
ffffffff80404736:       892a                    mv      s2,a0
ffffffff80404738:       001fd517                auipc   a0,0x1fd
ffffffff8040473c:       8c850513                addi    a0,a0,-1848 # ffffffff80601000 <load_pa>
ffffffff80404740:       4585                    li      a1,1
ffffffff80404742:       00b50023                sb      a1,0(a0)     // BUG!
ffffffff80404746:       001fd517                auipc   a0,0x1fd
ffffffff8040474a:       8c250513                addi    a0,a0,-1854 # ffffffff80601008 <load_sz>
ffffffff8040474e:       00b50023                sb      a1,0(a0)     // BUG!
ffffffff80404752:       ffbfc517                auipc   a0,0xffbfc
ffffffff80404756:       8ae50513                addi    a0,a0,-1874 # ffffffff80000000 <_start>
ffffffff8040475a:       55fd                    li      a1,-1
ffffffff8040475c:       02559613                slli    a2,a1,0x25
ffffffff80404760:       83018593                addi    a1,gp,-2000 # ffffffff80ca6428 <kernel_virt_addr>
ffffffff80404764:       618c                    ld      a1,0(a1)
ffffffff80404766:       8e09                    sub     a2,a2,a0
...

It seems load_pa and load_sz are stored with 1, this is obviously not what the
code expected. 


W/ WRITE_ONCE, the setup_vm() is compiled to:

ffffffff8040472a <setup_vm>:
ffffffff8040472a:       1101                    addi    sp,sp,-32
ffffffff8040472c:       ec06                    sd      ra,24(sp)
ffffffff8040472e:       e822                    sd      s0,16(sp)
ffffffff80404730:       e426                    sd      s1,8(sp)
ffffffff80404732:       e04a                    sd      s2,0(sp)
ffffffff80404734:       1000                    addi    s0,sp,32
ffffffff80404736:       892a                    mv      s2,a0
ffffffff80404738:       001fd597                auipc   a1,0x1fd
ffffffff8040473c:       8c858593                addi    a1,a1,-1848 # ffffffff80601000 <load_pa>
ffffffff80404740:       ffbfc517                auipc   a0,0xffbfc
ffffffff80404744:       8c050513                addi    a0,a0,-1856 # ffffffff80000000 <_start>
ffffffff80404748:       e188                    sd      a0,0(a1)
ffffffff8040474a:       001fd597                auipc   a1,0x1fd
ffffffff8040474e:       8be58593                addi    a1,a1,-1858 # ffffffff80601008 <load_sz>
ffffffff80404752:       4605                    li      a2,1
ffffffff80404754:       00c58023                sb      a2,0(a1)
ffffffff80404758:       55fd                    li      a1,-1
ffffffff8040475a:       02559613                slli    a2,a1,0x25
ffffffff8040475e:       83018593                addi    a1,gp,-2000 # ffffffff80ca6428 <kernel_virt_addr>
ffffffff80404762:       618c                    ld      a1,0(a1)
ffffffff80404764:       8e09                    sub     a2,a2,a0
...

This is what the code expected.