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SubjectRe: Linux 2.6.38-rc5
On Wed, Feb 16, 2011 at 07:46:20AM -0800, Linus Torvalds wrote:
> On Wed, Feb 16, 2011 at 3:14 AM, Eric Dumazet <eric.dumazet@gmail.com> wrote:
> >
> > Using this kernel on my dev machine (2x4x2 cpus), I hit BUG_ON() in
> > fs/namei.c:1461 on my kernel build (make -j16)
>
> Uhhuh. We replaced one BUG_ON() with another.
>
> And I think it's a really silly problem too: when Al moved the
>
> /* We drop rcu-walk here */
> if (nameidata_dentry_drop_rcu_maybe(nd, path->dentry))
> return -ECHILD;
>
> test into do_follow_link(), he _should_ have moved the BUG_ON() in
> there too, methinks. He didn't, and as a result the BUG_ON() is now
> before the "drop_rcu_maybe".
>
> This patch should fix it. Al? Comments?

Sigh... I see what's going on. We'd got inode from dentry that is getting
crapped under us. We will *not* survive dropping RCU - it's bad enough for
full restart in normal mode. So right after we'd seen that (already wrong)
inode has ->follow_link(), we decide to drop RCU. Originally this BUG_ON
hadn't been reached in that case - we had already failed with -ECHILD before
we got to it. Now we don't...

_However_, I don't like passing inode to do_follow_link(). I'd rather set
nd->inode to inode first and use it there. Let me think a bit and see if
it's feasible...


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