linux-kernel - Re: [PATCH] x86: Fix static memory detection

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Date:   Tue, 17 Mar 2020 06:44:31 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     x86@...nel.org
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH] x86: Fix static memory detection

ping ... I still see this problem.

Guenter

On Thu, Jan 30, 2020 at 06:11:59PM -0800, Guenter Roeck wrote:
> When booting x86 images in qemu, the following warning is seen
> randomly if DEBUG_LOCKDEP is enabled.
> 
> WARNING: CPU: 0 PID: 1 at kernel/locking/lockdep.c:1119
> 	lockdep_register_key+0xc0/0x100
> 
> static_obj() returns true if an address is between _stext and _end.
> On x86, this includes the brk memory space. Problem is that this
> memory block is not static on x86; its unused portions are released
> after init and can be allocated. This results in the observed warning
> if a lockdep object is allocated from this memory.
> 
> Solve the problem by implementing arch_is_kernel_initmem_freed()
> for x86 and have it return true if an address is within the released
> memory range.
> 
> The same problem was solved for s390 with commit 7a5da02de8d6e
> ("locking/lockdep: check for freed initmem in static_obj()"), which
> introduced arch_is_kernel_initmem_freed().
> 
> Signed-off-by: Guenter Roeck <linux@...ck-us.net>
> ---
>  arch/x86/include/asm/sections.h | 20 ++++++++++++++++++++
>  arch/x86/kernel/setup.c         |  1 -
>  2 files changed, 20 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/include/asm/sections.h b/arch/x86/include/asm/sections.h
> index 036c360910c5..a6e8373a5170 100644
> --- a/arch/x86/include/asm/sections.h
> +++ b/arch/x86/include/asm/sections.h
> @@ -2,6 +2,8 @@
>  #ifndef _ASM_X86_SECTIONS_H
>  #define _ASM_X86_SECTIONS_H
>  
> +#define arch_is_kernel_initmem_freed arch_is_kernel_initmem_freed
> +
>  #include <asm-generic/sections.h>
>  #include <asm/extable.h>
>  
> @@ -14,4 +16,22 @@ extern char __end_rodata_hpage_align[];
>  
>  extern char __end_of_kernel_reserve[];
>  
> +extern unsigned long _brk_start, _brk_end;
> +
> +static inline bool arch_is_kernel_initmem_freed(unsigned long addr)
> +{
> +	/*
> +	 * If _brk_start has not been cleared, brk allocation is incomplete,
> +	 * and we can not make assumptions about its use.
> +	 */
> +	if (_brk_start)
> +		return 0;
> +
> +	/*
> +	 * After brk allocation is complete, space between _brk_end and _end
> +	 * is available for allocation.
> +	 */
> +	return addr >= _brk_end && addr < (unsigned long)&_end;
> +}
> +
>  #endif	/* _ASM_X86_SECTIONS_H */
> diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
> index 1e4c20a1efec..08f5ceed70e0 100644
> --- a/arch/x86/kernel/setup.c
> +++ b/arch/x86/kernel/setup.c
> @@ -64,7 +64,6 @@ RESERVE_BRK(dmi_alloc, 65536);
>   * at link time, with RESERVE_BRK*() facility reserving additional
>   * chunks.
>   */
> -static __initdata
>  unsigned long _brk_start = (unsigned long)__brk_base;
>  unsigned long _brk_end   = (unsigned long)__brk_base;
>