[BUG-2.4.10] deadlock in do_truncate() and shmem_getpage()

Tachino Nobuhiro
2001-10-02T06:14:23Z

Hello,

I found a a deadlock bug in v2.4.10 due to invert locking order between
inode->i_truncate_sem and inode->i_sem.
Sequence is following.

do_truncate()
down(&inode->i_sem);
down_write(&inode->i_truncate_sem);

do_no_page()
down_read(&inode->i_truncate_sem);

shmem_nopage();
shmem_getpage();
down(&inode->i_sem);

Following patch works for me.

diff -r -u -N linux.org/fs/open.c linux/fs/open.c
--- linux.org/fs/open.c Tue Oct 2 11:35:47 2001
+++ linux/fs/open.c Tue Oct 2 11:45:33 2001
@@ -81,13 +81,13 @@
if (length < 0)
return -EINVAL;

- down(&inode->i_sem);
down_write(&inode->i_truncate_sem);
+ down(&inode->i_sem);
newattrs.ia_size = length;
newattrs.ia_valid = ATTR_SIZE | ATTR_CTIME;
error = notify_change(dentry, &newattrs);
- up_write(&inode->i_truncate_sem);
up(&inode->i_sem);
+ up_write(&inode->i_truncate_sem);
return error;
}