[PATCH] Take a writer lock for mmap_sem.

[Hollis Blanchard <hollisb@us.ibm.com>]

On Sat, 2007-07-07 at 10:20 +0100, Keir Fraser wrote:
> Changes inside powerpc files are fine. Obviously powerpc-specific changes
> inside common files are usually fine. Changes to locking protocols in common
> files (e.g., changed usage of mmap_sem in privcmd.c) is *not* fine. Please
> post patches for that kind of thing.

My mistake, I meant to send this separately.

In 2.6.17, we did our own locking inside direct_remap_pfn_range(). In
the current Linux tree though, the locking is done in privcmd_ioctl().

However, since direct_remap_pfn_range() is modifying the mm_struct,
shouldn't that be a a write lock rather than a read lock?



[XEN][LINUX] Take a writer lock for mmap_sem.
direct_remap_pfn_range() will be modifying the mm.
Signed-off-by: Christian Ehrhardt <ehrhardt@linux.vnet.ibm.com>
Signed-off-by: Hollis Blanchard <hollisb@us.ibm.com>

diff -r e5f633c33025 drivers/xen/privcmd/privcmd.c
--- a/drivers/xen/privcmd/privcmd.c	Fri Jul 06 17:35:53 2007 +0100
+++ b/drivers/xen/privcmd/privcmd.c	Mon Jul 09 10:07:32 2007 -0500
@@ -111,7 +112,7 @@ static int privcmd_ioctl(struct inode *i
 		if (copy_from_user(&msg, p, sizeof(msg)))
 			return -EFAULT;
 
-		down_read(&mm->mmap_sem);
+		down_write(&mm->mmap_sem);
 
 		vma = find_vma(mm, msg.va);
 		rc = -EINVAL;
@@ -153,7 +154,7 @@ static int privcmd_ioctl(struct inode *i
 		rc = 0;
 
 	mmap_out:
-		up_read(&mm->mmap_sem);
+		up_write(&mm->mmap_sem);
 		ret = rc;
 	}
 	break;
@@ -176,14 +177,14 @@ static int privcmd_ioctl(struct inode *i
 		if ((m.num <= 0) || (nr_pages > (LONG_MAX >> PAGE_SHIFT)))
 			return -EINVAL;
 
-		down_read(&mm->mmap_sem);
+		down_write(&mm->mmap_sem);
 
 		vma = find_vma(mm, m.addr);
 		if (!vma ||
 		    (m.addr != vma->vm_start) ||
 		    ((m.addr + (nr_pages << PAGE_SHIFT)) != vma->vm_end) ||
 		    !privcmd_enforce_singleshot_mapping(vma)) {
-			up_read(&mm->mmap_sem);
+			up_write(&mm->mmap_sem);
 			return -EINVAL;
 		}
 
@@ -191,7 +192,7 @@ static int privcmd_ioctl(struct inode *i
 		addr = m.addr;
 		for (i = 0; i < nr_pages; i++, addr += PAGE_SIZE, p++) {
 			if (get_user(mfn, p)) {
-				up_read(&mm->mmap_sem);
+				up_write(&mm->mmap_sem);
 				return -EFAULT;
 			}
 
@@ -202,7 +203,7 @@ static int privcmd_ioctl(struct inode *i
 				put_user(0xF0000000 | mfn, p);
 		}
 
-		up_read(&mm->mmap_sem);
+		up_write(&mm->mmap_sem);
 		ret = 0;
 	}
 	break;


-- 
Hollis Blanchard
IBM Linux Technology Center