[Xen-devel] [PATCH] Take a writer lock for mmap_sem.

[Hollis Blanchard <hollisb@xxxxxxxxxx>]

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@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Hollis Blanchard <hollisb@xxxxxxxxxx>

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


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