2001-10-02 06:14:23

by Tachino Nobuhiro

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

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;
}

2001-10-02 06:32:59

by Andrew Morton

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

Tachino Nobuhiro wrote:
>
> 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);
>

i_truncate_sem is introduced in the ext3 patch - it's not in
the standard 2.4.10.

> 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;
> }

Indeed. That's been there for months! Thanks.

-