Re: [PATCH] LoongArch: Fix lockdep static memory detection

[Helge Deller]

On 9/15/23 11:23, Huacai Chen wrote:
> On Fri, Sep 15, 2023 at 4:16 PM Helge Deller <deller@xxxxxx> wrote:
> > On 9/15/23 05:22, Huacai Chen wrote:
> > > Hi Helge,
> > >
> > > On Wed, Sep 13, 2023 at 3:18 AM Helge Deller <deller@xxxxxx> wrote:
> > > > Since commit 0a6b58c5cd0d ("lockdep: fix static memory detection even
> > > > more") the lockdep code uses is_kernel_core_data(), is_kernel_rodata()
> > > > and init_section_contains() to verify if a lock is located inside a
> > > > kernel static data section.
> > > >
> > > > This change triggers a failure on LoongArch, for which the vmlinux.lds.S
> > > > script misses to put the locks (as part of in the .data.rel symbols)
> > > > into the Linux data section.
> > > > This patch fixes the lockdep problem by moving *(.data.rel*) symbols
> > > > into the kernel data section (from _sdata to _edata).
> > > >
> > > > Additionally, move other wrongly assigned symbols too:
> > > > - altinstructions into the _initdata section,
> >
> > > I think altinstructions cannot  be put into _initdata because it will
> > > be used by modules.
> >
> > No.
> > arch/loongarch/kernel/vmlinux.lds.S is used for the static parts of the kernel
> > and altinstructions are replaced before modules are loaded.
> > For altinstructions in modules the linker script scripts/module.lds.S is used.

> OK, then what about .got/.plt? It seems arm64 also doesn't put them in
> the data section.

arm64 seems to throw away all plt entries already at link time (and just keeps
the got.plt in the read-only data section).
It even checks at link time, that there are no plt entries in the binary:
        ASSERT(SIZEOF(.plt) == 0, "Unexpected run-time procedure linkages detected!")

I don't know for loongarch, but if you need the plt entries for loongarch, it's
safest & best to put them into the read-only data section too, which is what my patch does.
Up to now, you have them completely outside of code & data sections.

In the end you need to decide for your platform. My patch is a suggestion, which I think
is correct (untested by me, but Guenter replied he tested it).
But to fix the lockdep problem at minimum the move of the .data.rel section
is needed.

Helge

> > > > - PLT symbols behind the read-only section, and
> > > > - *(.la_abs) into the data section.
> > > >
> > > > Signed-off-by: Helge Deller <deller@xxxxxx>
> > > > Reported-by: Guenter Roeck <linux@xxxxxxxxxxxx>
> > > > Fixes: 0a6b58c5cd0d ("lockdep: fix static memory detection even more")
> > > > Cc: stable <stable@xxxxxxxxxx> # v6.4+
> > > >
> > > > diff --git a/arch/loongarch/kernel/vmlinux.lds.S b/arch/loongarch/kernel/vmlinux.lds.S
> > > > index b1686afcf876..bb2ec86f37a8 100644
> > > > --- a/arch/loongarch/kernel/vmlinux.lds.S
> > > > +++ b/arch/loongarch/kernel/vmlinux.lds.S
> > > > @@ -53,33 +53,6 @@ SECTIONS
> > > >           . = ALIGN(PECOFF_SEGMENT_ALIGN);
> > > >           _etext = .;
> > > >
> > > > -       /*
> > > > -        * struct alt_inst entries. From the header (alternative.h):
> > > > -        * "Alternative instructions for different CPU types or capabilities"
> > > > -        * Think locking instructions on spinlocks.
> > > > -        */
> > > > -       . = ALIGN(4);
> > > > -       .altinstructions : AT(ADDR(.altinstructions) - LOAD_OFFSET) {
> > > > -               __alt_instructions = .;
> > > > -               *(.altinstructions)
> > > > -               __alt_instructions_end = .;
> > > > -       }
> > > > -
> > > > -#ifdef CONFIG_RELOCATABLE
> > > > -       . = ALIGN(8);
> > > > -       .la_abs : AT(ADDR(.la_abs) - LOAD_OFFSET) {
> > > > -               __la_abs_begin = .;
> > > > -               *(.la_abs)
> > > > -               __la_abs_end = .;
> > > > -       }
> > > > -#endif
> > > > -
> > > > -       .got : ALIGN(16) { *(.got) }
> > > > -       .plt : ALIGN(16) { *(.plt) }
> > > > -       .got.plt : ALIGN(16) { *(.got.plt) }
> > > > -
> > > > -       .data.rel : { *(.data.rel*) }
> > > > -
> > > >           . = ALIGN(PECOFF_SEGMENT_ALIGN);
> > > >           __init_begin = .;
> > > >           __inittext_begin = .;
> > > > @@ -94,6 +67,18 @@ SECTIONS
> > > >
> > > >           __initdata_begin = .;
> > > >
> > > > +       /*
> > > > +        * struct alt_inst entries. From the header (alternative.h):
> > > > +        * "Alternative instructions for different CPU types or capabilities"
> > > > +        * Think locking instructions on spinlocks.
> > > > +        */
> > > > +       . = ALIGN(4);
> > > > +       .altinstructions : AT(ADDR(.altinstructions) - LOAD_OFFSET) {
> > > > +               __alt_instructions = .;
> > > > +               *(.altinstructions)
> > > > +               __alt_instructions_end = .;
> > > > +       }
> > > > +
> > > >           INIT_DATA_SECTION(16)
> > > >           .exit.data : {
> > > >                   EXIT_DATA
> > > > @@ -113,6 +98,11 @@ SECTIONS
> > > >
> > > >           _sdata = .;
> > > >           RO_DATA(4096)
> > > > +
> > > > +       .got : ALIGN(16) { *(.got) }
> > > > +       .plt : ALIGN(16) { *(.plt) }
> > > > +       .got.plt : ALIGN(16) { *(.got.plt) }
> > > > +
> > > >           RW_DATA(1 << CONFIG_L1_CACHE_SHIFT, PAGE_SIZE, THREAD_SIZE)
> > > >
> > > >           .rela.dyn : ALIGN(8) {
> > > > @@ -121,6 +111,17 @@ SECTIONS
> > > >                   __rela_dyn_end = .;
> > > >           }
> > > >
> > > > +       .data.rel : { *(.data.rel*) }
> > > > +
> > > > +#ifdef CONFIG_RELOCATABLE
> > > > +       . = ALIGN(8);
> > > > +       .la_abs : AT(ADDR(.la_abs) - LOAD_OFFSET) {
> > > > +               __la_abs_begin = .;
> > > > +               *(.la_abs)
> > > > +               __la_abs_end = .;
> > > > +       }
> > > > +#endif
> > > > +
> > > >           .sdata : {
> > > >                   *(.sdata)
> > > >           }