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Subject: Re: [PATCH 3/3] resource: Fix find_next_iomem_res() iteration issue
To:     Bjorn Helgaas <helgaas@kernel.org>
Cc:     dan.j.williams@intel.com, brijesh.singh@amd.com, bhe@redhat.com,
        thomas.lendacky@amd.com, tiwai@suse.de, x86@kernel.org,
        kexec@lists.infradead.org, linux-kernel@vger.kernel.org,
        mingo@redhat.com, baiyaowei@cmss.chinamobile.com, hpa@zytor.com,
        tglx@linutronix.de, bp@suse.de, dyoung@redhat.com,
        akpm@linux-foundation.org, Vivek Goyal <vgoyal@redhat.com>
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 <13084ce6-e29a-c244-3f9c-cf0725646d9f@redhat.com>
 <20180927140351.GA257735@bhelgaas-glaptop.roam.corp.google.com>
From:   lijiang <lijiang@redhat.com>
Message-ID: <caec9ff1-f654-b4ea-ae3b-78ff2d073ee5@redhat.com>
Date:   Fri, 28 Sep 2018 13:09:37 +0800
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在 2018年09月27日 22:03, Bjorn Helgaas 写道:
> On Thu, Sep 27, 2018 at 01:27:41PM +0800, lijiang wrote:
>> 在 2018年09月25日 06:15, Bjorn Helgaas 写道:
>>> From: Bjorn Helgaas <bhelgaas@google.com>
>>>
>>> Previously find_next_iomem_res() used "*res" as both an input parameter for
>>> the range to search and the type of resource to search for, and an output
>>> parameter for the resource we found, which makes the interface confusing
>>> and hard to use correctly.
>>>
>>> All callers allocate a single struct resource and use it for repeated calls
>>> to find_next_iomem_res().  When find_next_iomem_res() returns a resource,
>>> it overwrites the start, end, flags, and desc members of the struct.  If we
>>> call find_next_iomem_res() again, we must update or restore these fields.
>>>
>>> The callers (__walk_iomem_res_desc() and walk_system_ram_range()) do not
>>> restore res->flags, so if the caller is searching for flags of
>>> IORESOURCE_MEM | IORESOURCE_BUSY and finds a resource with flags of
>>> IORESOURCE_MEM | IORESOURCE_BUSY | IORESOURCE_SYSRAM, the next search will
>>> find only resources marked as IORESOURCE_SYSRAM.
>>>
>>> Fix this by restructuring the interface so it takes explicit "start, end,
>>> flags" parameters and uses "*res" only as an output parameter.
>>
>> Hi, Bjorn
>> I personally suggest that some comments might be added in the code, make it clear
>> and easy to understand, then which could avoid the old confusion and more code changes.
> 
> Since I think the current interface (using *res as both input and
> output parameters that have very different meanings) is confusing,
> it's hard for *me* to write comments that make it less confusing, but
> of course, you're welcome to propose something.
> 
> My opinion (probably not universally shared) is that my proposal would
> make the code more readable, and it's worth doing even though the diff
> is larger.
> 
> Anyway, I'll post these patches independently and see if anybody else
> has an opinion.
> 

I don't mind at all, because that is just my own opinion about more code
changes.

Anyway, thank you to improve this patch.

Regards,
Lianbo

> Bjorn
> 
>>> Original-patch: http://lore.kernel.org/lkml/20180921073211.20097-2-lijiang@redhat.com
>>> Based-on-patch-by: Lianbo Jiang <lijiang@redhat.com>
>>> Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
>>> ---
>>>  kernel/resource.c |   94 +++++++++++++++++++++++------------------------------
>>>  1 file changed, 41 insertions(+), 53 deletions(-)
>>>
>>> diff --git a/kernel/resource.c b/kernel/resource.c
>>> index 155ec873ea4d..9891ea90cc8f 100644
>>> --- a/kernel/resource.c
>>> +++ b/kernel/resource.c
>>> @@ -319,23 +319,26 @@ int release_resource(struct resource *old)
>>>  EXPORT_SYMBOL(release_resource);
>>>  
>>>  /*
>>> - * Finds the lowest iomem resource existing within [res->start..res->end].
>>> - * The caller must specify res->start, res->end, res->flags, and optionally
>>> - * desc.  If found, returns 0, res is overwritten, if not found, returns -1.
>>> - * This function walks the whole tree and not just first level children until
>>> - * and unless first_level_children_only is true.
>>> + * Finds the lowest iomem resource that covers part of [start..end].  The
>>> + * caller must specify start, end, flags, and desc (which may be
>>> + * IORES_DESC_NONE).
>>> + *
>>> + * If a resource is found, returns 0 and *res is overwritten with the part
>>> + * of the resource that's within [start..end]; if none is found, returns
>>> + * -1.
>>> + *
>>> + * This function walks the whole tree and not just first level children
>>> + * unless first_level_children_only is true.
>>>   */
>>> -static int find_next_iomem_res(struct resource *res, unsigned long desc,
>>> -			       bool first_level_children_only)
>>> +static int find_next_iomem_res(resource_size_t start, resource_size_t end,
>>> +			       unsigned long flags, unsigned long desc,
>>> +			       bool first_level_children_only,
>>> +			       struct resource *res)
>>>  {
>>> -	resource_size_t start, end;
>>>  	struct resource *p;
>>>  	bool sibling_only = false;
>>>  
>>>  	BUG_ON(!res);
>>> -
>>> -	start = res->start;
>>> -	end = res->end;
>>>  	BUG_ON(start >= end);
>>>  
>>>  	if (first_level_children_only)
>>> @@ -344,7 +347,7 @@ static int find_next_iomem_res(struct resource *res, unsigned long desc,
>>>  	read_lock(&resource_lock);
>>>  
>>>  	for (p = iomem_resource.child; p; p = next_resource(p, sibling_only)) {
>>> -		if ((p->flags & res->flags) != res->flags)
>>> +		if ((p->flags & flags) != flags)
>>>  			continue;
>>>  		if ((desc != IORES_DESC_NONE) && (desc != p->desc))
>>>  			continue;
>>> @@ -359,32 +362,31 @@ static int find_next_iomem_res(struct resource *res, unsigned long desc,
>>>  	read_unlock(&resource_lock);
>>>  	if (!p)
>>>  		return -1;
>>> +
>>>  	/* copy data */
>>> -	if (res->start < p->start)
>>> -		res->start = p->start;
>>> -	if (res->end > p->end)
>>> -		res->end = p->end;
>>> +	res->start = max(start, p->start);
>>> +	res->end = min(end, p->end);
>>>  	res->flags = p->flags;
>>>  	res->desc = p->desc;
>>>  	return 0;
>>>  }
>>>  
>>> -static int __walk_iomem_res_desc(struct resource *res, unsigned long desc,
>>> -				 bool first_level_children_only,
>>> -				 void *arg,
>>> +static int __walk_iomem_res_desc(resource_size_t start, resource_size_t end,
>>> +				 unsigned long flags, unsigned long desc,
>>> +				 bool first_level_children_only, void *arg,
>>>  				 int (*func)(struct resource *, void *))
>>>  {
>>> -	u64 orig_end = res->end;
>>> +	struct resource res;
>>>  	int ret = -1;
>>>  
>>> -	while ((res->start < res->end) &&
>>> -	       !find_next_iomem_res(res, desc, first_level_children_only)) {
>>> -		ret = (*func)(res, arg);
>>> +	while (start < end &&
>>> +	       !find_next_iomem_res(start, end, flags, desc,
>>> +				    first_level_children_only, &res)) {
>>> +		ret = (*func)(&res, arg);
>>>  		if (ret)
>>>  			break;
>>>  
>>> -		res->start = res->end + 1;
>>> -		res->end = orig_end;
>>> +		start = res.end + 1;
>>>  	}
>>>  
>>>  	return ret;
>>> @@ -407,13 +409,7 @@ static int __walk_iomem_res_desc(struct resource *res, unsigned long desc,
>>>  int walk_iomem_res_desc(unsigned long desc, unsigned long flags, u64 start,
>>>  		u64 end, void *arg, int (*func)(struct resource *, void *))
>>>  {
>>> -	struct resource res;
>>> -
>>> -	res.start = start;
>>> -	res.end = end;
>>> -	res.flags = flags;
>>> -
>>> -	return __walk_iomem_res_desc(&res, desc, false, arg, func);
>>> +	return __walk_iomem_res_desc(start, end, flags, desc, false, arg, func);
>>>  }
>>>  EXPORT_SYMBOL_GPL(walk_iomem_res_desc);
>>>  
>>> @@ -427,13 +423,9 @@ EXPORT_SYMBOL_GPL(walk_iomem_res_desc);
>>>  int walk_system_ram_res(u64 start, u64 end, void *arg,
>>>  				int (*func)(struct resource *, void *))
>>>  {
>>> -	struct resource res;
>>> -
>>> -	res.start = start;
>>> -	res.end = end;
>>> -	res.flags = IORESOURCE_SYSTEM_RAM | IORESOURCE_BUSY;
>>> +	unsigned long flags = IORESOURCE_SYSTEM_RAM | IORESOURCE_BUSY;
>>>  
>>> -	return __walk_iomem_res_desc(&res, IORES_DESC_NONE, true,
>>> +	return __walk_iomem_res_desc(start, end, flags, IORES_DESC_NONE, true,
>>>  				     arg, func);
>>>  }
>>>  
>>> @@ -444,13 +436,9 @@ int walk_system_ram_res(u64 start, u64 end, void *arg,
>>>  int walk_mem_res(u64 start, u64 end, void *arg,
>>>  		 int (*func)(struct resource *, void *))
>>>  {
>>> -	struct resource res;
>>> -
>>> -	res.start = start;
>>> -	res.end = end;
>>> -	res.flags = IORESOURCE_MEM | IORESOURCE_BUSY;
>>> +	unsigned long flags = IORESOURCE_MEM | IORESOURCE_BUSY;
>>>  
>>> -	return __walk_iomem_res_desc(&res, IORES_DESC_NONE, true,
>>> +	return __walk_iomem_res_desc(start, end, flags, IORES_DESC_NONE, true,
>>>  				     arg, func);
>>>  }
>>>  
>>> @@ -464,25 +452,25 @@ int walk_mem_res(u64 start, u64 end, void *arg,
>>>  int walk_system_ram_range(unsigned long start_pfn, unsigned long nr_pages,
>>>  		void *arg, int (*func)(unsigned long, unsigned long, void *))
>>>  {
>>> +	resource_size_t start, end;
>>> +	unsigned long flags;
>>>  	struct resource res;
>>>  	unsigned long pfn, end_pfn;
>>> -	u64 orig_end;
>>>  	int ret = -1;
>>>  
>>> -	res.start = (u64) start_pfn << PAGE_SHIFT;
>>> -	res.end = ((u64)(start_pfn + nr_pages) << PAGE_SHIFT) - 1;
>>> -	res.flags = IORESOURCE_SYSTEM_RAM | IORESOURCE_BUSY;
>>> -	orig_end = res.end;
>>> -	while ((res.start < res.end) &&
>>> -		(find_next_iomem_res(&res, IORES_DESC_NONE, true) >= 0)) {
>>> +	start = (u64) start_pfn << PAGE_SHIFT;
>>> +	end = ((u64)(start_pfn + nr_pages) << PAGE_SHIFT) - 1;
>>> +	flags = IORESOURCE_SYSTEM_RAM | IORESOURCE_BUSY;
>>> +	while (start < end &&
>>> +	       !find_next_iomem_res(start, end, flags, IORES_DESC_NONE,
>>> +				    true, &res)) {
>>>  		pfn = (res.start + PAGE_SIZE - 1) >> PAGE_SHIFT;
>>>  		end_pfn = (res.end + 1) >> PAGE_SHIFT;
>>>  		if (end_pfn > pfn)
>>>  			ret = (*func)(pfn, end_pfn - pfn, arg);
>>>  		if (ret)
>>>  			break;
>>> -		res.start = res.end + 1;
>>> -		res.end = orig_end;
>>> +		start = res.end + 1;
>>>  	}
>>>  	return ret;
>>>  }
>>>
>>>
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