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SubjectRe: [git pull] vfs fixes
On Mon, Apr 10, 2017 at 11:10:19PM -0700, Linus Torvalds wrote:

> It looks odd because the lock part is
> if (flags & LOOKUP_RCU)
> rcu_read_lock();
> ie it's locked conditionally, and the code in between does not seem to
> return every time LOOKUP_RCU is clear.
> So mind giving this a look? Is it as obviously buggy as I think it is,
> or is there something I'm missing?

It's more obscure than I would like, and can grow into a bug one day, but...
nd_jump_root() can only return non-zero if you have LOOKUP_RCU. So without
LOOKUP_RCU in flags, this
if (flags & LOOKUP_RCU)
if (likely(!nd_jump_root(nd)))
return s;
nd->root.mnt = NULL;
won't get to that rcu_read_unlock() at all - it'll get zero from nd_jump_root()
and proceed to return s;

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