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SubjectRe: [PATCH v3 10/12] ima: defer calling __fput()
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On Thu, 2012-03-22 at 14:22 +0000, Al Viro wrote:
> On Wed, Mar 21, 2012 at 02:54:15PM -0400, Mimi Zohar wrote:
> > If a file is closed before it is munmapped, __fput() is called with
> > the mmap_sem taken. With IMA-appraisal enabled, this results in an
> > mmap_sem/i_mutex lockdep. ima_defer_fput() increments the f_count
> > to defer __fput() being called until after the mmap_sem is released.
>
> NAK. It's far too heavy-weight for what's a very common path. Worse,
> it causes different locking conditions on IMA and non-IMA kernels and makes
> bugs harder to spot. Rejected with extreme prejudice; please, fix your
> locking instead.

Al, thanks for replying! I realize you are very prejudiced against IMA,
but have you taken a look at IMA-appraisal? It probably would have been
better if we used another name in order to avoid this prejudice, but
unfortunately we didn't. :( IMA-appraisal is about enforcing file
integrity.

> BTW, you've missed several other places in mm/* doing fput(), so it wouldn't
> be enough to paper over your problem anyway.
>
> Final fput() *can* happen under mmap_sem. Period.

I think I got that loud and clear; otherwise we wouldn't have come up
with deferring the __fput(). We have a very real problem here - writing
extended attributes requires taking the i_mutex. I'm open to any
suggestions.

thanks,

Mimi



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