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

[Luiz Fernando N. Capitulino]

Em Mon, 6 Aug 2007 09:46:08 +0200
Ingo Molnar <[EMAIL PROTECTED]> 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();
 


-- 
Luiz Fernando N. Capitulino
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