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

From: Tachino Nobuhiro (tachino@open.nm.fujitsu.co.jp)
Date: Tue Oct 02 2001 - 01:14:21 EST


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;
 }
 
-
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