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Subject: Re: [PATCH] device-dax: Fix range release
To:     Dan Williams <dan.j.williams@intel.com>,
        <linux-nvdimm@lists.01.org>
CC:     Jane Chu <jane.chu@oracle.com>, <linux-kernel@vger.kernel.org>
References: <160834570161.1791850.14911670304441510419.stgit@dwillia2-desk3.amr.corp.intel.com>
From:   "Leizhen (ThunderTown)" <thunder.leizhen@huawei.com>
Message-ID: <a51de4b3-521a-1455-1236-02d813842c8c@huawei.com>
Date:   Sat, 19 Dec 2020 15:46:03 +0800
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On 2020/12/19 10:41, Dan Williams wrote:
> There are multiple locations that open-code the release of the last
> range in a device-dax instance. Consolidate this into a new
> dev_dax_trim_range() helper.
> 
> This also addresses a kmemleak report:
> 
> # cat /sys/kernel/debug/kmemleak
> [..]
> unreferenced object 0xffff976bd46f6240 (size 64):
>    comm "ndctl", pid 23556, jiffies 4299514316 (age 5406.733s)
>    hex dump (first 32 bytes):
>      00 00 00 00 00 00 00 00 00 00 20 c3 37 00 00 00  .......... .7...
>      ff ff ff 7f 38 00 00 00 00 00 00 00 00 00 00 00  ....8...........
>    backtrace:
>      [<00000000064003cf>] __kmalloc_track_caller+0x136/0x379
>      [<00000000d85e3c52>] krealloc+0x67/0x92
>      [<00000000d7d3ba8a>] __alloc_dev_dax_range+0x73/0x25c
>      [<0000000027d58626>] devm_create_dev_dax+0x27d/0x416
>      [<00000000434abd43>] __dax_pmem_probe+0x1c9/0x1000 [dax_pmem_core]
>      [<0000000083726c1c>] dax_pmem_probe+0x10/0x1f [dax_pmem]
>      [<00000000b5f2319c>] nvdimm_bus_probe+0x9d/0x340 [libnvdimm]
>      [<00000000c055e544>] really_probe+0x230/0x48d
>      [<000000006cabd38e>] driver_probe_device+0x122/0x13b
>      [<0000000029c7b95a>] device_driver_attach+0x5b/0x60
>      [<0000000053e5659b>] bind_store+0xb7/0xc3
>      [<00000000d3bdaadc>] drv_attr_store+0x27/0x31
>      [<00000000949069c5>] sysfs_kf_write+0x4a/0x57
>      [<000000004a8b5adf>] kernfs_fop_write+0x150/0x1e5
>      [<00000000bded60f0>] __vfs_write+0x1b/0x34
>      [<00000000b92900f0>] vfs_write+0xd8/0x1d1
> 
> Reported-by: Jane Chu <jane.chu@oracle.com>
> Cc: Zhen Lei <thunder.leizhen@huawei.com>
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
> ---
>  drivers/dax/bus.c |   44 +++++++++++++++++++++-----------------------
>  1 file changed, 21 insertions(+), 23 deletions(-)
> 
> diff --git a/drivers/dax/bus.c b/drivers/dax/bus.c
> index 9761cb40d4bb..720cd140209f 100644
> --- a/drivers/dax/bus.c
> +++ b/drivers/dax/bus.c
> @@ -367,19 +367,28 @@ void kill_dev_dax(struct dev_dax *dev_dax)
>  }
>  EXPORT_SYMBOL_GPL(kill_dev_dax);
>  
> -static void free_dev_dax_ranges(struct dev_dax *dev_dax)
> +static void trim_dev_dax_range(struct dev_dax *dev_dax)
>  {
> +	int i = dev_dax->nr_range - 1;
> +	struct range *range = &dev_dax->ranges[i].range;
>  	struct dax_region *dax_region = dev_dax->region;
> -	int i;
>  
>  	device_lock_assert(dax_region->dev);
> -	for (i = 0; i < dev_dax->nr_range; i++) {
> -		struct range *range = &dev_dax->ranges[i].range;
> -
> -		__release_region(&dax_region->res, range->start,
> -				range_len(range));
> +	dev_dbg(&dev_dax->dev, "delete range[%d]: %#llx:%#llx\n", i,
> +		(unsigned long long)range->start,
> +		(unsigned long long)range->end);
> +
> +	__release_region(&dax_region->res, range->start, range_len(range));
> +	if (--dev_dax->nr_range == 0) {
> +		kfree(dev_dax->ranges);
> +		dev_dax->ranges = NULL;
>  	}
> -	dev_dax->nr_range = 0;
> +}
> +
> +static void free_dev_dax_ranges(struct dev_dax *dev_dax)
> +{
> +	while (dev_dax->nr_range)
It's better to use READ_ONCE to get the value of dev_dax->nr_range,
to prevent compiler optimization.

> +		trim_dev_dax_range(dev_dax);
>  }
>  
>  static void unregister_dev_dax(void *dev)
> @@ -804,15 +813,10 @@ static int alloc_dev_dax_range(struct dev_dax *dev_dax, u64 start,
>  		return 0;
>  
>  	rc = devm_register_dax_mapping(dev_dax, dev_dax->nr_range - 1);
> -	if (rc) {
> -		dev_dbg(dev, "delete range[%d]: %pa:%pa\n", dev_dax->nr_range - 1,
> -				&alloc->start, &alloc->end);
> -		dev_dax->nr_range--;
> -		__release_region(res, alloc->start, resource_size(alloc));
> -		return rc;
> -	}
> +	if (rc)
> +		trim_dev_dax_range(dev_dax);
>  
> -	return 0;
> +	return rc;
>  }
>  
>  static int adjust_dev_dax_range(struct dev_dax *dev_dax, struct resource *res, resource_size_t size)
> @@ -885,12 +889,7 @@ static int dev_dax_shrink(struct dev_dax *dev_dax, resource_size_t size)
>  		if (shrink >= range_len(range)) {
>  			devm_release_action(dax_region->dev,
>  					unregister_dax_mapping, &mapping->dev);
> -			__release_region(&dax_region->res, range->start,
> -					range_len(range));
> -			dev_dax->nr_range--;
> -			dev_dbg(dev, "delete range[%d]: %#llx:%#llx\n", i,
> -					(unsigned long long) range->start,
> -					(unsigned long long) range->end);
> +			trim_dev_dax_range(dev_dax);
>  			to_shrink -= shrink;
>  			if (!to_shrink)
>  				break;
> @@ -1267,7 +1266,6 @@ static void dev_dax_release(struct device *dev)
>  	put_dax(dax_dev);
>  	free_dev_dax_id(dev_dax);
>  	dax_region_put(dax_region);
> -	kfree(dev_dax->ranges);
>  	kfree(dev_dax->pgmap);
>  	kfree(dev_dax);
>  }
> 
> 
> .
>