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SubjectRe: kernel Ooops (2.5.63 bk latest)
Maneesh Soni <maneesh@in.ibm.com> wrote:
>
> Hi Linus,
>
> The BUG was caught in d_validate() --> dget(). I think the
> dentry to be validated can be already on LRU list with d_count
> as zero. So, dget_locked should be used in place of dget().
> dcache_rcu mistakingly used dget. This patch corrects it.
>
> Please apply the following patch.
>
> diff -urN linux-2.5.63-bk3/fs/dcache.c linux-2.5.63-bk3-d_validate/fs/dcache.c
> --- linux-2.5.63-bk3/fs/dcache.c 2003-02-28 12:06:09.000000000 +0530
> +++ linux-2.5.63-bk3-d_validate/fs/dcache.c 2003-02-28 12:16:30.000000000 +0530
> @@ -1056,7 +1056,7 @@
> * as it is parsed under dcache_lock
> */
> if (dentry == list_entry(lhp, struct dentry, d_hash)) {
> - dget(dentry);
> + __dget_locked(dentry);
> spin_unlock(&dcache_lock);
> return 1;

Is this correct? If smbfs is playing around with dentries which are on
dentry_unused and which have a zero refcount then these can be freed up at
any time. The filesystem should have taken a ref on the dentry to prevent it
from being scavenged.

Isn't the bug over in smb_fill_cache(), which does:

newdent = d_lookup(...);
...
ctl.cache->dentry[ctl.idx] = newdent;
...
dput(newdent);

I suspect we need to take an extra ref on the dentry when it is copied to the
cache, and put that ref back when smb_readdir() has finished using the dentry
(it looks like it's already doing that).

If so, the same problem is present in 2.4, but nobody noticed because 2.4 is
already using __dget_locked() and escapes the BUG check.

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