2.6.11-rc2-mm1: kernel bad access while booting diskless client

[Albert Herranz]

Hi,

I'm getting a kernel Oops while booting 2.6.11-rc2-mm1
on a diskless (nfsroot based) embedded ppc system.
Vanilla 2.6.11-rc2 works Ok.

[...]
VFS: Mounted root (nfs filesystem) readonly.
Freeing unused kernel memory: 112k init
INIT: version 2.86 booting
Oops: kernel access of bad area, sig: 11 [#1]
[...]
TASK = c1643ae0[1] 'init' THREAD: c1646000
Last syscall: 106
[...]
NIP [c0060934] vfs_getattr+0x1c/0xa8
LR [c0060a14] vfs_stat+0x54/0x64
Call trace:
 [c0060a14] vfs_sysstat+0x54/0x64
 [c0060f24] sys_newstat+0x1c/0x54
 [c0003c40] ret_from_syscall+0x0/0x44
Kernel panic - not syncing: Attempted to kill init!


The cause of the bad access is a null inode->i_op
field that is passed to vfs_getattr() through the
corresponding struct dentry.
It triggers when vfs_getattr() blindly tries to check
inode->i_op->getattr without first checking that
inode->i_op is useable.

The attached patch workarounds the problem, by
checking inode->i_op before using it.

It is still unknown to me which code change is causing
now the appearance of the null i_op field on -rc2-mm1.
But probably you guys have better clues than me.

Cheers,
Albert



	
	
		
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http://correo.yahoo.es--- a/fs/stat.c	2004-12-24 22:34:02.000000000 +0100
+++ b/fs/stat.c	2005-01-27 00:52:15.000000000 +0100
@@ -47,7 +47,7 @@ int vfs_getattr(struct vfsmount *mnt, st
 	if (retval)
 		return retval;
 
-	if (inode->i_op->getattr)
+	if (inode->i_op && inode->i_op->getattr)
 		return inode->i_op->getattr(mnt, dentry, stat);
 
 	generic_fillattr(inode, stat);