Re: [PATCH] i386: convert mm_context_t semaphore to a mutex

Luiz Fernando N. Capitulino
2007-08-06T13:49:24Z

Em Mon, 6 Aug 2007 09:46:08 +0200
Ingo Molnar <mingo@elte.hu> escreveu:

|
| > typedef struct {
| > int size;
| > - struct semaphore sem;
| > + struct mutex lock;
|
| hm, looks good to me but i'm wondering why this was a holdout for such a
| long time :-) Did you manage to test actual LDT functionality with this
| patch applied?

No, I didn't. The only test I did was to run the kernel with this
patch applied.

I'll manage to test it then. Do you have a test-case or has any
suggestion?

Oh, btw, I forgot to 'quilt add arch/i386/mm/fault.c' so the
patch I sent was incomplete. Fixed version below. Shame on me.

[PATCH] i386: convert mm_context_t semaphore to a mutex

---
arch/i386/kernel/i386_ksyms.c | 1 +
arch/i386/kernel/ldt.c | 14 +++++++-------
arch/i386/kernel/ptrace.c | 4 ++--
arch/i386/mm/fault.c | 4 ++--
include/asm-i386/mmu.h | 4 ++--
5 files changed, 14 insertions(+), 13 deletions(-)

--- linux-2.6-lcpt.orig/arch/i386/kernel/ldt.c
+++ linux-2.6-lcpt/arch/i386/kernel/ldt.c
@@ -94,13 +94,13 @@ int init_new_context(struct task_struct
struct mm_struct * old_mm;
int retval = 0;

- init_MUTEX(&mm->context.sem);
+ mutex_init(&mm->context.lock);
mm->context.size = 0;
old_mm = current->mm;
if (old_mm && old_mm->context.size > 0) {
- down(&old_mm->context.sem);
+ mutex_lock(&old_mm->context.lock);
retval = copy_ldt(&mm->context, &old_mm->context);
- up(&old_mm->context.sem);
+ mutex_unlock(&old_mm->context.lock);
}
return retval;
}
@@ -132,7 +132,7 @@ static int read_ldt(void __user * ptr, u
if (bytecount > LDT_ENTRY_SIZE*LDT_ENTRIES)
bytecount = LDT_ENTRY_SIZE*LDT_ENTRIES;

- down(&mm->context.sem);
+ mutex_lock(&mm->context.lock);
size = mm->context.size*LDT_ENTRY_SIZE;
if (size > bytecount)
size = bytecount;
@@ -140,7 +140,7 @@ static int read_ldt(void __user * ptr, u
err = 0;
if (copy_to_user(ptr, mm->context.ldt, size))
err = -EFAULT;
- up(&mm->context.sem);
+ mutex_unlock(&mm->context.lock);
if (err < 0)
goto error_return;
if (size != bytecount) {
@@ -196,7 +196,7 @@ static int write_ldt(void __user * ptr,
goto out;
}

- down(&mm->context.sem);
+ mutex_lock(&mm->context.lock);
if (ldt_info.entry_number >= mm->context.size) {
error = alloc_ldt(&current->mm->context, ldt_info.entry_number+1, 1);
if (error < 0)
@@ -223,7 +223,7 @@ install:
error = 0;

out_unlock:
- up(&mm->context.sem);
+ mutex_unlock(&mm->context.lock);
out:
return error;
}
--- linux-2.6-lcpt.orig/arch/i386/kernel/ptrace.c
+++ linux-2.6-lcpt/arch/i386/kernel/ptrace.c
@@ -166,7 +166,7 @@ static unsigned long convert_eip_to_line

seg &= ~7UL;

- down(&child->mm->context.sem);
+ mutex_lock(&child->mm->context.lock);
if (unlikely((seg >> 3) >= child->mm->context.size))
addr = -1L; /* bogus selector, access would fault */
else {
@@ -180,7 +180,7 @@ static unsigned long convert_eip_to_line
addr &= 0xffff;
addr += base;
}
- up(&child->mm->context.sem);
+ mutex_unlock(&child->mm->context.lock);
}
return addr;
}
--- linux-2.6-lcpt.orig/include/asm-i386/mmu.h
+++ linux-2.6-lcpt/include/asm-i386/mmu.h
@@ -1,7 +1,7 @@
#ifndef __i386_MMU_H
#define __i386_MMU_H

-#include <asm/semaphore.h>
+#include <linux/mutex.h>
/*
* The i386 doesn't have a mmu context, but
* we put the segment information here.
@@ -10,7 +10,7 @@
*/
typedef struct {
int size;
- struct semaphore sem;
+ struct mutex lock;
void *ldt;
void *vdso;
} mm_context_t;
--- linux-2.6-lcpt.orig/arch/i386/kernel/i386_ksyms.c
+++ linux-2.6-lcpt/arch/i386/kernel/i386_ksyms.c
@@ -1,4 +1,5 @@
#include <linux/module.h>
+#include <asm/semaphore.h>
#include <asm/checksum.h>
#include <asm/desc.h>

--- linux-2.6-lcpt.orig/arch/i386/mm/fault.c
+++ linux-2.6-lcpt/arch/i386/mm/fault.c
@@ -110,7 +110,7 @@ static inline unsigned long get_segment_
LDT and other horrors are only used in user space. */
if (seg & (1<<2)) {
/* Must lock the LDT while reading it. */
- down(&current->mm->context.sem);
+ mutex_lock(&current->mm->context.lock);
desc = current->mm->context.ldt;
desc = (void *)desc + (seg & ~7);
} else {
@@ -123,7 +123,7 @@ static inline unsigned long get_segment_
base = get_desc_base((unsigned long *)desc);

if (seg & (1<<2)) {
- up(&current->mm->context.sem);
+ mutex_unlock(&current->mm->context.lock);
} else
put_cpu();