linux-kernel - Re: [PATCH 4/6] UML - free() wrapper should call libc free

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Message-ID: <4637FC1D.4040300@yahoo.com.au>
Date:	Wed, 02 May 2007 12:49:01 +1000
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Jeff Dike <jdike@...toit.com>
CC:	akpm@...l.org, LKML <linux-kernel@...r.kernel.org>,
	uml-devel <user-mode-linux-devel@...ts.sourceforge.net>
Subject: Re: [PATCH 4/6] UML - free() wrapper should call libc free

Jeff Dike wrote:
> The libc free wrapper wasn't correctly detecting buffers obtained with
> malloc().  This is now done by seeing if the page was reserved.  This is
> the case for memory which is left aside for libc and isn't given to
> the page allocator.  If we free a pointer in a reserved page, it is
> given to free() rather than kfree().

I want to get rid of PG_reserved eventually. Is it possible to use PG_arch_1
for this?

> 
> Signed-off-by: Jeff Dike <jdike@...ux.intel.com>
> --
>  arch/um/include/user.h   |    1 +
>  arch/um/kernel/um_arch.c |    7 +++++++
>  arch/um/os-Linux/main.c  |    6 +++++-
>  3 files changed, 13 insertions(+), 1 deletion(-)
> 
> Index: linux-2.6.21-mm/arch/um/include/user.h
> ===================================================================
> --- linux-2.6.21-mm.orig/arch/um/include/user.h	2007-04-26 17:33:01.000000000 -0400
> +++ linux-2.6.21-mm/arch/um/include/user.h	2007-04-27 14:21:35.000000000 -0400
> @@ -27,5 +27,6 @@ extern int in_aton(char *str);
>  extern int open_gdb_chan(void);
>  extern size_t strlcpy(char *, const char *, size_t);
>  extern size_t strlcat(char *, const char *, size_t);
> +extern int reserved_address(void *addr);
>  
>  #endif
> Index: linux-2.6.21-mm/arch/um/kernel/um_arch.c
> ===================================================================
> --- linux-2.6.21-mm.orig/arch/um/kernel/um_arch.c	2007-04-26 17:41:21.000000000 -0400
> +++ linux-2.6.21-mm/arch/um/kernel/um_arch.c	2007-04-27 14:30:36.000000000 -0400
> @@ -500,6 +500,13 @@ void __init check_bugs(void)
>  	os_check_bugs();
>  }
>  
> +int reserved_address(void *addr)
> +{
> +	struct page *page = virt_to_page(addr);
> +
> +	return(PageReserved(page));
> +}
> +
>  void apply_alternatives(struct alt_instr *start, struct alt_instr *end)
>  {
>  }
> Index: linux-2.6.21-mm/arch/um/os-Linux/main.c
> ===================================================================
> --- linux-2.6.21-mm.orig/arch/um/os-Linux/main.c	2007-04-26 17:41:10.000000000 -0400
> +++ linux-2.6.21-mm/arch/um/os-Linux/main.c	2007-04-27 14:30:31.000000000 -0400
> @@ -266,6 +266,8 @@ void __wrap_free(void *ptr)
>  	/* We need to know how the allocation happened, so it can be correctly
>  	 * freed.  This is done by seeing what region of memory the pointer is
>  	 * in -
> +	 *	in a reserved page - free, assume the pointer was
> +	 *	    acquired with malloc, since it couldn't have been kmalloced.
>  	 * 	physical memory - kmalloc/kfree
>  	 *	kernel virtual memory - vmalloc/vfree
>  	 * 	anywhere else - malloc/free
> @@ -281,7 +283,9 @@ void __wrap_free(void *ptr)
>  	 * there is a possibility for memory leaks.
>  	 */
>  
> -	if((addr >= uml_physmem) && (addr < high_physmem)){
> +	if(kmalloc_ok && reserved_address(ptr))
> +		__real_free(ptr);
> +	else if((addr >= uml_physmem) && (addr < high_physmem)){
>  		if(CAN_KMALLOC())
>  			kfree(ptr);
>  	}
> -
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> 


-- 
SUSE Labs, Novell Inc.
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