From: Waiman Long <longman@redhat.com>
To: David Laight <David.Laight@ACULAB.COM>, Christoph Hellwig <hch@lst.de>
Cc: Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>, Will Deacon <will.deacon@arm.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"stable@vger.kernel.org" <stable@vger.kernel.org>
Subject: Re: [PATCH] locking/rwsem: Fix kernel crash when spinning on RWSEM_OWNER_UNKNOWN
Date: Wed, 15 Jan 2020 10:47:49 -0500 [thread overview]
Message-ID: <4ac00b33-5397-3c69-6cba-cf3d9d375ea9@redhat.com> (raw)
In-Reply-To: <45b976af3cf74555af7214993e7d614b@AcuMS.aculab.com>
On 1/15/20 10:16 AM, David Laight wrote:
> From: linux-kernel-owner@vger.kernel.org <linux-kernel-owner@vger.kernel.org> On Behalf Of Waiman Long
>> Sent: 15 January 2020 14:27
> ...
>>>> if ((wstate == WRITER_HANDOFF) &&
>>>> - (rwsem_spin_on_owner(sem, 0) == OWNER_NULL))
>>>> + rwsem_spin_on_owner(sem, RWSEM_NONSPINNABLE) == OWNER_NULL)
>>> Nit: the inner braces in the first half of the conditional aren't required
>>> either.
>> I typically over-parenthesize the code to make it easier to read as we
>> don't need to think too much about operator precedence to see if it is
>> doing the right thing.
> The problem is it actually makes it harder to read.
> It is difficult for the 'mark 1 eyeball' to follow lots of sets of brackets.
> Since == (etc) are the lowest priority operators (apart from ?:) they
> never need ().
>
> David
>
> -
> Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
> Registration No: 1397386 (Wales)
>
It depends. I find it hard to read an expression with "&" and "&&"
without parentheses. Anyway, I will admit that the above code is
inconsistent in term of how parentheses are used. So I will change that.
Cheers,
Longman
next prev parent reply other threads:[~2020-01-15 15:47 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-14 19:03 [PATCH] locking/rwsem: Fix kernel crash when spinning on RWSEM_OWNER_UNKNOWN Waiman Long
2020-01-15 6:50 ` Christoph Hellwig
2020-01-15 14:27 ` Waiman Long
2020-01-15 15:16 ` David Laight
2020-01-15 15:47 ` Waiman Long [this message]
2020-01-15 16:01 ` David Laight
2020-01-15 15:28 ` Waiman Long
2020-01-15 15:37 ` Peter Zijlstra
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