From: Hugh Dickins <hugh@veritas.com>
Why is mapping->truncate_count atomic? It's incremented inside i_mmap_lock
(and i_sem), and the reads don't need it to be atomic.
And why smp_rmb() before call to ->nopage? The compiler cannot reorder the
initial assignment of sequence after the call to ->nopage, and no cpu (yet!)
can read from the future, which is all that matters there.
And delete totally bogus reset of truncate_count from blkmtd add_device.
truncate_count is all about detecting i_size changes: i_size does not change
there; and if it did, the count should be incremented not reset.
Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
---
25-akpm/drivers/mtd/devices/blkmtd.c | 1 -
25-akpm/fs/inode.c | 1 -
25-akpm/include/linux/fs.h | 2 +-
25-akpm/mm/memory.c | 12 +++++-------
4 files changed, 6 insertions(+), 10 deletions(-)
diff -puN drivers/mtd/devices/blkmtd.c~vmtrunc-truncate_count-not-atomic drivers/mtd/devices/blkmtd.c
--- 25/drivers/mtd/devices/blkmtd.c~vmtrunc-truncate_count-not-atomic 2004-11-30 01:23:44.830951768 -0800
+++ 25-akpm/drivers/mtd/devices/blkmtd.c 2004-11-30 01:23:44.839950400 -0800
@@ -661,7 +661,6 @@ static struct blkmtd_dev *add_device(cha
memset(dev, 0, sizeof(struct blkmtd_dev));
dev->blkdev = bdev;
- atomic_set(&(dev->blkdev->bd_inode->i_mapping->truncate_count), 0);
if(!readonly) {
init_MUTEX(&dev->wrbuf_mutex);
}
diff -puN fs/inode.c~vmtrunc-truncate_count-not-atomic fs/inode.c
--- 25/fs/inode.c~vmtrunc-truncate_count-not-atomic 2004-11-30 01:23:44.832951464 -0800
+++ 25-akpm/fs/inode.c 2004-11-30 01:23:44.840950248 -0800
@@ -201,7 +201,6 @@ void inode_init_once(struct inode *inode
INIT_RADIX_TREE(&inode->i_data.page_tree, GFP_ATOMIC);
rwlock_init(&inode->i_data.tree_lock);
spin_lock_init(&inode->i_data.i_mmap_lock);
- atomic_set(&inode->i_data.truncate_count, 0);
INIT_LIST_HEAD(&inode->i_data.private_list);
spin_lock_init(&inode->i_data.private_lock);
INIT_PRIO_TREE_ROOT(&inode->i_data.i_mmap);
diff -puN include/linux/fs.h~vmtrunc-truncate_count-not-atomic include/linux/fs.h
--- 25/include/linux/fs.h~vmtrunc-truncate_count-not-atomic 2004-11-30 01:23:44.833951312 -0800
+++ 25-akpm/include/linux/fs.h 2004-11-30 01:23:44.842949944 -0800
@@ -342,7 +342,7 @@ struct address_space {
struct prio_tree_root i_mmap; /* tree of private and shared mappings */
struct list_head i_mmap_nonlinear;/*list VM_NONLINEAR mappings */
spinlock_t i_mmap_lock; /* protect tree, count, list */
- atomic_t truncate_count; /* Cover race condition with truncate */
+ unsigned int truncate_count; /* Cover race condition with truncate */
unsigned long nrpages; /* number of total pages */
pgoff_t writeback_index;/* writeback starts here */
struct address_space_operations *a_ops; /* methods */
diff -puN mm/memory.c~vmtrunc-truncate_count-not-atomic mm/memory.c
--- 25/mm/memory.c~vmtrunc-truncate_count-not-atomic 2004-11-30 01:23:44.835951008 -0800
+++ 25-akpm/mm/memory.c 2004-11-30 01:23:44.844949640 -0800
@@ -1421,7 +1421,7 @@ void unmap_mapping_range(struct address_
spin_lock(&mapping->i_mmap_lock);
/* Protect against page fault */
- atomic_inc(&mapping->truncate_count);
+ mapping->truncate_count++;
if (unlikely(!prio_tree_empty(&mapping->i_mmap)))
unmap_mapping_range_list(&mapping->i_mmap, &details);
@@ -1724,7 +1724,7 @@ do_no_page(struct mm_struct *mm, struct
struct page * new_page;
struct address_space *mapping = NULL;
pte_t entry;
- int sequence = 0;
+ unsigned int sequence = 0;
int ret = VM_FAULT_MINOR;
int anon = 0;
@@ -1736,9 +1736,8 @@ do_no_page(struct mm_struct *mm, struct
if (vma->vm_file) {
mapping = vma->vm_file->f_mapping;
- sequence = atomic_read(&mapping->truncate_count);
+ sequence = mapping->truncate_count;
}
- smp_rmb(); /* Prevent CPU from reordering lock-free ->nopage() */
retry:
cond_resched();
new_page = vma->vm_ops->nopage(vma, address & PAGE_MASK, &ret);
@@ -1772,9 +1771,8 @@ retry:
* invalidated this page. If unmap_mapping_range got called,
* retry getting the page.
*/
- if (mapping &&
- (unlikely(sequence != atomic_read(&mapping->truncate_count)))) {
- sequence = atomic_read(&mapping->truncate_count);
+ if (mapping && unlikely(sequence != mapping->truncate_count)) {
+ sequence = mapping->truncate_count;
spin_unlock(&mm->page_table_lock);
page_cache_release(new_page);
goto retry;
_