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From: "J. R. Okajima" <hooanon05g@gmail.com>
Subject: Re: Q: lockdep_assert_held_read() after downgrade_write()
To: Peter Zijlstra <peterz@infradead.org>
Cc: Jens Axboe <axboe@fb.com>, linux-kernel@vger.kernel.org,
        darrick.wong@oracle.com, david@fromorbit.com
In-Reply-To: <20170131163253.GQ6515@twins.programming.kicks-ass.net>
References: <18295.1485811542@jrobl> <86195df9-2a43-2a0f-38ac-68792edc41c0@fb.com> <5873.1485877203@jrobl> <20170131163253.GQ6515@twins.programming.kicks-ass.net>
Date: Fri, 03 Feb 2017 01:33:21 +0900
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Peter Zijlstra:
> Does something like the below work better? The annotation in
> downgrade_write() would look something like:
>
> +	lock_downgrade(&sem->dep_map, 1, _RET_IP_);
>
> Not even compile tested and lacks the !LOCKDEP build bits.

Thanks for the patch.
It seems working expectedly. I began writing a similar patch locally
with minor consolidations by adding a new function or two. I will send a
patch series. Please review and merge them into v4.10. If you don't like
the patch, especially the new function name, feel free to change it.
I don't know whether !LOCKDEP build bits are necessary or not.


J. R. Okajima