--On Wednesday, June 04, 2003 15:38:09 -0700 Andrew Morton <akpm@digeo.com>
wrote:
>> After more careful consideration, I don't see any reasons why
>> page_table_lock is necessary for dealing with vmas. I found one spot in
>> swapoff, but it was easily changed to mmap_sem.
>
> What keeps the VMA tree consistent when try_to_unmap_one()
> runs find_vma()?
Gah. I don't know how I convinced myself that code was safe. It's easily
fixed. How does this one look?
Dave
======================================================================
Dave McCracken IBM Linux Base Kernel Team 1-512-838-3059
dmccr@us.ibm.com T/L 678-3059
--==========996000887==========
Content-Type: text/plain; charset=iso-8859-1; name="nolock-2.5.70-mm4-2.diff"
Content-Transfer-Encoding: quoted-printable
Content-Disposition: attachment; filename="nolock-2.5.70-mm4-2.diff";
size=5473
--- 2.5.70-mm4/./mm/swapfile.c 2003-05-26 20:00:25.000000000 -0500
+++ 2.5.70-mm4-nolock/./mm/swapfile.c 2003-06-04 16:02:49.000000000 -0500
@@ -493,6 +493,7 @@ static int unuse_process(struct mm_struc
/*
* Go through process' page directory.
*/
+ down_read(&mm->mmap_sem);
spin_lock(&mm->page_table_lock);
for (vma =3D mm->mmap; vma; vma =3D vma->vm_next) {
pgd_t * pgd =3D pgd_offset(mm, vma->vm_start);
@@ -500,6 +501,7 @@ static int unuse_process(struct mm_struc
break;
}
spin_unlock(&mm->page_table_lock);
+ up_read(&mm->mmap_sem);
pte_chain_free(pte_chain);
return 0;
}
--- 2.5.70-mm4/./mm/mmap.c 2003-06-04 15:47:24.000000000 -0500
+++ 2.5.70-mm4-nolock/./mm/mmap.c 2003-06-04 16:02:49.000000000 -0500
@@ -346,9 +346,7 @@ static void vma_link(struct mm_struct *m
=20
if (mapping)
down(&mapping->i_shared_sem);
- spin_lock(&mm->page_table_lock);
__vma_link(mm, vma, prev, rb_link, rb_parent);
- spin_unlock(&mm->page_table_lock);
if (mapping)
up(&mapping->i_shared_sem);
=20
@@ -429,7 +427,6 @@ static int vma_merge(struct mm_struct *m
unsigned long end, unsigned long vm_flags,
struct file *file, unsigned long pgoff)
{
- spinlock_t * lock =3D &mm->page_table_lock;
=20
/*
* We later require that vma->vm_flags =3D=3D vm_flags, so this tests
@@ -458,7 +455,6 @@ static int vma_merge(struct mm_struct *m
down(&inode->i_mapping->i_shared_sem);
need_up =3D 1;
}
- spin_lock(lock);
prev->vm_end =3D end;
=20
/*
@@ -471,7 +467,6 @@ static int vma_merge(struct mm_struct *m
prev->vm_end =3D next->vm_end;
__vma_unlink(mm, next, prev);
__remove_shared_vm_struct(next, inode);
- spin_unlock(lock);
if (need_up)
up(&inode->i_mapping->i_shared_sem);
if (file)
@@ -481,7 +476,6 @@ static int vma_merge(struct mm_struct *m
kmem_cache_free(vm_area_cachep, next);
return 1;
}
- spin_unlock(lock);
if (need_up)
up(&inode->i_mapping->i_shared_sem);
return 1;
@@ -497,10 +491,8 @@ static int vma_merge(struct mm_struct *m
pgoff, (end - addr) >> PAGE_SHIFT))
return 0;
if (end =3D=3D prev->vm_start) {
- spin_lock(lock);
prev->vm_start =3D addr;
prev->vm_pgoff -=3D (end - addr) >> PAGE_SHIFT;
- spin_unlock(lock);
return 1;
}
}
@@ -945,19 +937,16 @@ int expand_stack(struct vm_area_struct *
*/
address +=3D 4 + PAGE_SIZE - 1;
address &=3D PAGE_MASK;
- spin_lock(&vma->vm_mm->page_table_lock);
grow =3D (address - vma->vm_end) >> PAGE_SHIFT;
=20
/* Overcommit.. */
if (!vm_enough_memory(grow)) {
- spin_unlock(&vma->vm_mm->page_table_lock);
return -ENOMEM;
}
if (address - vma->vm_start > current->rlim[RLIMIT_STACK].rlim_cur ||
((vma->vm_mm->total_vm + grow) << PAGE_SHIFT) >
current->rlim[RLIMIT_AS].rlim_cur) {
- spin_unlock(&vma->vm_mm->page_table_lock);
vm_unacct_memory(grow);
return -ENOMEM;
}
@@ -965,7 +954,6 @@ int expand_stack(struct vm_area_struct *
vma->vm_mm->total_vm +=3D grow;
if (vma->vm_flags & VM_LOCKED)
vma->vm_mm->locked_vm +=3D grow;
- spin_unlock(&vma->vm_mm->page_table_lock);
return 0;
}
=20
@@ -999,19 +987,16 @@ int expand_stack(struct vm_area_struct *
* the spinlock only before relocating the vma range ourself.
*/
address &=3D PAGE_MASK;
- spin_lock(&vma->vm_mm->page_table_lock);
grow =3D (vma->vm_start - address) >> PAGE_SHIFT;
=20
/* Overcommit.. */
if (!vm_enough_memory(grow)) {
- spin_unlock(&vma->vm_mm->page_table_lock);
return -ENOMEM;
}
if (vma->vm_end - address > current->rlim[RLIMIT_STACK].rlim_cur ||
((vma->vm_mm->total_vm + grow) << PAGE_SHIFT) >
current->rlim[RLIMIT_AS].rlim_cur) {
- spin_unlock(&vma->vm_mm->page_table_lock);
vm_unacct_memory(grow);
return -ENOMEM;
}
@@ -1020,7 +1005,6 @@ int expand_stack(struct vm_area_struct *
vma->vm_mm->total_vm +=3D grow;
if (vma->vm_flags & VM_LOCKED)
vma->vm_mm->locked_vm +=3D grow;
- spin_unlock(&vma->vm_mm->page_table_lock);
return 0;
}
=20
@@ -1183,8 +1167,6 @@ static void unmap_region(struct mm_struc
/*
* Create a list of vma's touched by the unmap, removing them from the =
mm's
* vma list as we go..
- *
- * Called with the page_table_lock held.
*/
static void
detach_vmas_to_be_unmapped(struct mm_struct *mm, struct vm_area_struct =
*vma,
@@ -1308,8 +1290,8 @@ int do_munmap(struct mm_struct *mm, unsi
/*
* Remove the vma's, and unmap the actual pages
*/
- spin_lock(&mm->page_table_lock);
detach_vmas_to_be_unmapped(mm, mpnt, prev, end);
+ spin_lock(&mm->page_table_lock);
unmap_region(mm, mpnt, prev, start, end);
spin_unlock(&mm->page_table_lock);
=20
--- 2.5.70-mm4/./mm/rmap.c 2003-06-04 15:47:24.000000000 -0500
+++ 2.5.70-mm4-nolock/./mm/rmap.c 2003-06-04 17:52:13.000000000 -0500
@@ -305,12 +305,21 @@ static int try_to_unmap_one(struct page=20
BUG();
=20
/*
+ * Take mmap_sem across the find_vma call. We need to take it before
+ * the spinlock.
+ */
+ if (!down_read_trylock(&mm->mmap_sem)) {
+ ret =3D SWAP_AGAIN;
+ goto out_unmap;
+ }
+
+ /*
* We need the page_table_lock to protect us from page faults,
* munmap, fork, etc...
*/
if (!spin_trylock(&mm->page_table_lock)) {
- rmap_ptep_unmap(ptep);
- return SWAP_AGAIN;
+ ret =3D SWAP_AGAIN;
+ goto out_unlock_sem;
}
=20
=20
@@ -371,8 +380,11 @@ static int try_to_unmap_one(struct page=20
ret =3D SWAP_SUCCESS;
=20
out_unlock:
- rmap_ptep_unmap(ptep);
spin_unlock(&mm->page_table_lock);
+out_unlock_sem:
+ up_read(&mm->mmap_sem);
+out_unmap:
+ rmap_ptep_unmap(ptep);
return ret;
}
=20
--==========996000887==========--
-
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