lkml.org 
[lkml]   [2005]   [Nov]   [22]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: What protection does sysfs_readdir have with SMP/Preemption?
On Tue, Nov 22, 2005 at 04:33:22PM -0500, Steven Rostedt wrote:
> Hi,
>
> I'm developing a custom kernel on top of Ingo's -rt patch. My kernel
> makes race conditions in the vanilla kernel show up very well :-)
>
> I just hit a bug, actually a page fault in fs/sysfs/dir.c in
> sysfs_readdir:
>
>
>
> for (p=q->next; p!= &parent_sd->s_children; p=p->next) {
> struct sysfs_dirent *next;
> const char * name;
> int len;
>
> next = list_entry(p, struct sysfs_dirent,
> s_sibling);
> if (!next->s_element)
> continue;
>
> name = sysfs_get_name(next);
> len = strlen(name);
> if (next->s_dentry)
> ino = next->s_dentry->d_inode->i_ino;
>
> ^^^^
> This is where I had a bad pointer reference.
>
> else
> ino = iunique(sysfs_sb, 2);
>
> if (filldir(dirent, name, len, filp->f_pos, ino,
> dt_type(next)) < 0)
> return 0;
>
>
> Looking at this code, I don't see anything protecting the s_dentry. For
> example, couldn't the following happen:
>
> sysfs_create_dir is called, which calls create_dir. Now we create a
> dentry with no d_inode. In sysfs_make_dirent which calls
> sysfs_new_dirent which adds to the parents s_children. Then
> sysfs_make_dirent sets s_dentry = dentry (the one that was just made
> with no d_inode assigned yet). Then create_dir calls sysfs_create which
> finally assigns the d_inode.
>
> So, either there is some hidden protection and my modification to the
> kernel has caused this to bug, or we have just been lucky the whole time
> in the vanilla kernel.

I think we've been lucky :(

Maneesh, any ideas?

thanks,

greg k-h
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2005-11-22 22:44    [W:0.075 / U:0.860 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site