[PATCH 4/6] UML - free() wrapper should call libc free

[PATCH 4/6] UML - free() wrapper should call libc free

[Jeff Dike]

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().

Signed-off-by: Jeff Dike <jdike@linux.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);
 	}

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

[Nick Piggin]

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@linux.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.

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

[Jeff Dike]

On Wed, May 02, 2007 at 12:49:01PM +1000, Nick Piggin wrote:
> I want to get rid of PG_reserved eventually. Is it possible to use PG_arch_1
> for this?

Yup.

Andrew - Feel free to drop this or just sit on it until I send a
replacement.  Whichever is easier.

				Jeff

-- 
Work email - jdike at linux dot intel dot com