linux-kernel - Re: [PATCH v5 03/18] wlcore: simplify/fix/optimize reg_ch_conf

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Message-ID: <02f06de8-ebb2-24ff-27e1-f697cadc02c4@redhat.com>
Date:   Fri, 15 Mar 2019 18:17:06 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Fenghua Yu <fenghua.yu@...el.com>,
        Kalle Valo <kvalo@...eaurora.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, H Peter Anvin <hpa@...or.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Ashok Raj <ashok.raj@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Xiaoyao Li <xiaoyao.li@...el.com>,
        Michael Chan <michael.chan@...adcom.com>,
        Ravi V Shankar <ravi.v.shankar@...el.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        x86 <x86@...nel.org>, linux-wireless@...r.kernel.org,
        netdev@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH v5 03/18] wlcore: simplify/fix/optimize
 reg_ch_conf_pending operations

On 15/03/19 00:16, Fenghua Yu wrote:
> Hi, Valo,
> 
> On Thu, Mar 14, 2019 at 03:16:33PM +0200, Kalle Valo wrote:
>> Fenghua Yu <fenghua.yu@...el.com> writes:
>>
>>> From: Paolo Bonzini <pbonzini@...hat.com>
>>>
>>> Bitmaps are defined on unsigned longs, so the usage of u32[2] in the
>>> wlcore driver is incorrect.  As noted by Peter Zijlstra, casting arrays
>>> to a bitmap is incorrect for big-endian architectures.
>>>
>>> When looking at it I observed that:
>>>
>>> - operations on reg_ch_conf_pending is always under the wl_lock mutex,
>>> so set_bit is overkill
>>>
>>> - the only case where reg_ch_conf_pending is accessed a u32 at a time is
>>> unnecessary too.
>>>
>>> This patch cleans up everything in this area, and changes tmp_ch_bitmap
>>> to have the proper alignment.
>>>
>>> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
>>> Signed-off-by: Fenghua Yu <fenghua.yu@...el.com>
>>
>> [...]
>>
>>>  int wlcore_cmd_regdomain_config_locked(struct wl1271 *wl)
>>>  {
>>>  	struct wl12xx_cmd_regdomain_dfs_config *cmd = NULL;
>>>  	int ret = 0, i, b, ch_bit_idx;
>>> -	u32 tmp_ch_bitmap[2];
>>> +	u32 tmp_ch_bitmap[2] __aligned(sizeof(unsigned long));
>>>  	struct wiphy *wiphy = wl->hw->wiphy;
>>>  	struct ieee80211_supported_band *band;
>>>  	bool timeout = false;
>>
>> [...]
>>
>>> @@ -1754,8 +1751,8 @@ int wlcore_cmd_regdomain_config_locked(struct wl1271 *wl)
>>>  		goto out;
>>>  	}
>>>  
>>> -	cmd->ch_bit_map1 = cpu_to_le32(tmp_ch_bitmap[0]);
>>> -	cmd->ch_bit_map2 = cpu_to_le32(tmp_ch_bitmap[1]);
>>> +	cmd->ch_bit_map1 = tmp_ch_bitmap[0];
>>> +	cmd->ch_bit_map2 = tmp_ch_bitmap[1];
>>
>> Will sparse still be happy? AFAICS you are now assigning u32 to __le32:
>>
>> struct wl12xx_cmd_regdomain_dfs_config {
>>        struct wl1271_cmd_header header;
>>
>>        __le32 ch_bit_map1;
>>        __le32 ch_bit_map2;
> 
> Discussion between Peter and Paolo (https://lkml.org/lkml/2019/3/4/521)
> may answer your question.

No, Kalle is right.  You do need to change

-	u32 tmp_ch_bitmap[2];
+	u32 tmp_ch_bitmap[2] __aligned(sizeof(unsigned long));

into

-	u32 tmp_ch_bitmap[2];
+	__le32 tmp_ch_bitmap[2] __aligned(sizeof(unsigned long));

The assignment from wl->reg_ch_conf_pending to tmp_ch_bitmap is fine
because it goes through memcpy.

Paolo

> (Sorry I didn't send to you v4 patch set)
> 
>>
>> Also this doesn't depend on anything else from this patchset, right? So
>> I could apply this directly?
> 
> You are right. This patch doesn't rely on other patches from this patchset.
> This patch just fixes a split lock issue. You could apply this directly
> without other patches.
> 
> Thanks.
> 
> -Fenghua
>