Message-ID: <c300747a-cf81-0e2d-77ec-f861421291f9@huaweicloud.com>
Date:   Thu, 26 Jan 2023 10:42:07 +0100
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Subject: Re: [PATCH] Fix data race in mark_rt_mutex_waiters
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To:     Waiman Long <longman@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>
Cc:     paulmck@kernel.org, Arjan van de Ven <arjan@linux.intel.com>,
        mingo@redhat.com, will@kernel.org, boqun.feng@gmail.com,
        akpm@osdl.org, tglx@linutronix.de, joel@joelfernandes.org,
        stern@rowland.harvard.edu, diogo.behrens@huawei.com,
        jonas.oberhauser@huawei.com, linux-kernel@vger.kernel.org,
        Hernan Ponce de Leon <hernanl.leon@huawei.com>,
        stable@vger.kernel.org,
        Jonas Oberhauser <jonas.oberhauser@huaweicloud.com>
References: <20230120135525.25561-1-hernan.poncedeleon@huaweicloud.com>
 <562c883b-b2c3-3a27-f045-97e7e3281e0b@linux.intel.com>
 <20230120155439.GI2948950@paulmck-ThinkPad-P17-Gen-1>
 <9a1c7959-4b8c-94df-a3e2-e69be72bfd7d@huaweicloud.com>
 <20230123164014.GN2948950@paulmck-ThinkPad-P17-Gen-1>
 <f17dcce0-d510-a112-3127-984e8e73f480@huaweicloud.com>
 <d1e28124-b7a7-ae19-87ec-b1dcd3701b61@redhat.com>
 <Y8/+2YBRD4rFySjh@hirez.programming.kicks-ass.net>
 <ae90e931-df19-9d60-610c-57dc34494d8e@redhat.com>
From:   Hernan Ponce de Leon <hernan.poncedeleon@huaweicloud.com>
In-Reply-To: <ae90e931-df19-9d60-610c-57dc34494d8e@redhat.com>
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On 1/24/2023 5:04 PM, Waiman Long wrote:
> 
> On 1/24/23 10:52, Peter Zijlstra wrote:
>> On Tue, Jan 24, 2023 at 10:42:24AM -0500, Waiman Long wrote:
>>
>>> I would suggest to do it as suggested by PeterZ. Instead of set_bit(),
>>> however, it is probably better to use atomic_long_or() like
>>>
>>> atomic_long_or_relaxed(RT_MUTEX_HAS_WAITERS, (atomic_long_t 
>>> *)&lock->owner)
>> That function doesn't exist, atomic_long_or() is implicitly relaxed for
>> not returning a value.
>>
> You are right. atomic_long_or() doesn't have variants like some others.
> 
> Cheers,
> Longman
> 

When you say "replace the whole of that function", do you mean "barrier 
included"? I argue in the other email that I think this should not 
affect correctness (at least not obviously), but removing the barrier is 
doing more than just fixing the data race as this patch suggests.

Hernan