linux-kernel - Re: [RFC PATCH 02/34] msm: clock: Always use an array to iterate over clocks

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Date:	Wed, 02 Nov 2011 14:34:03 -0700
From:	Stephen Boyd <sboyd@...eaurora.org>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
CC:	David Brown <davidb@...eaurora.org>,
	Daniel Walker <dwalker@...o99.com>,
	Bryan Huntsman <bryanh@...eaurora.org>,
	linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [RFC PATCH 02/34] msm: clock: Always use an array to iterate
 over clocks

On 11/02/11 12:45, Russell King - ARM Linux wrote:
> On Wed, Nov 02, 2011 at 11:35:59AM -0700, David Brown wrote:
>> If the array of clk_lookups contains aliases for the same struct
>> clk, msm_clock_init() will add the clock to the clocks list
>> twice.  This would cause list corruption so let's just remove the
>> clocks list and any associated code and iterate over the array
>> instead.
> Hmm...
>
>> @@ -158,13 +152,13 @@ void __init msm_clock_init(struct clk_lookup *clock_tbl, unsigned num_clocks)
>>   */
>>  static int __init clock_late_init(void)
>>  {
>> +	unsigned i, count = 0;
>>  	unsigned long flags;
>> -	struct clk *clk;
>> -	unsigned count = 0;
>>  
>>  	clock_debug_init();
>> -	mutex_lock(&clocks_mutex);
>> -	list_for_each_entry(clk, &clocks, list) {
>> +	for (i = 0; i < msm_num_clocks; i++) {
>> +		struct clk *clk = msm_clocks[i].clk;
>> +
>>  		clock_debug_add(clk);
> This means you'll end up calling clock_debug_add() twice for the same
> struct clk - this sounds like a bad idea in itself.  It looks like
> there's no protection within that function against it being called
> twice with the same struct clk.
>
> Are you sure this is safe?

This hasn't proven to be a problem so far because debugfs returns an
error when you create a directory with the same name twice. If we ever
do something more in clock_debug_add() we would have a problem.

-- 
Sent by an employee of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.

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