Re: I_CLEAR bug while shrinking dcache

From: Al Viro
Date: Tue Apr 14 2015 - 08:44:42 EST

On Tue, Apr 14, 2015 at 10:12:54AM +0200, Samuel Thibault wrote:

> So it seems that shrink_dentry_list was trying to kill an inode which
> already has I_CLEAR. I'll be trying the attached patch in the next
> days.

That patch is just papering over the problem. What you have is a dentry
with ->d_inode pointing to something with I_CLEAR set.

So either
* dentry has already been through __dentry_kill()
* or you have live dentry with ->d_inode somehow not contributing
to refcount of ->d_inode
* or you have an inode with positive refcount and I_CLEAR set.

The first variant can happen, but in that case it should have had
DCACHE_DENTRY_KILLED set by said __dentry_kill() and skipped. The other
two are clear inode refcounting bugs.

Do you have a reproducer for that?
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