linux-ext4 - Re: [PATCH v3 1/1] dax: Fix stack overflow when mounting fsdax pmem device

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Date:   Fri, 18 Sep 2020 16:59:42 +0530
From:   Ritesh Harjani <riteshh@...ux.ibm.com>
To:     Adrian Huang <adrianhuang0701@...il.com>, linux-nvdimm@...ts.01.org
Cc:     Yi Zhang <yi.zhang@...hat.com>,
        Mikulas Patocka <mpatocka@...hat.com>, Jan Kara <jack@...e.cz>,
        Adrian Huang <ahuang12@...ovo.com>, Coly Li <colyli@...e.de>,
        linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v3 1/1] dax: Fix stack overflow when mounting fsdax pmem
 device

ccing fs list

On 9/17/20 4:45 PM, Adrian Huang wrote:
> From: Adrian Huang <ahuang12@...ovo.com>
> 
> When mounting fsdax pmem device, commit 6180bb446ab6 ("dax: fix
> detection of dax support for non-persistent memory block devices")
> introduces the stack overflow [1][2]. Here is the call path for
> mounting ext4 file system:
>    ext4_fill_super
>      bdev_dax_supported
>        __bdev_dax_supported
>          dax_supported
>            generic_fsdax_supported
>              __generic_fsdax_supported
>                bdev_dax_supported
> 
> The call path leads to the infinite calling loop, so we cannot
> call bdev_dax_supported() in __generic_fsdax_supported(). The sanity
> checking of the variable 'dax_dev' is moved prior to the two
> bdev_dax_pgoff() checks [3][4].
> 
> [1] https://lore.kernel.org/linux-nvdimm/1420999447.1004543.1600055488770.JavaMail.zimbra@redhat.com/
> [2] https://lore.kernel.org/linux-nvdimm/alpine.LRH.2.02.2009141131220.30651@file01.intranet.prod.int.rdu2.redhat.com/
> [3] https://lore.kernel.org/linux-nvdimm/CA+RJvhxBHriCuJhm-D8NvJRe3h2MLM+ZMFgjeJjrRPerMRLvdg@mail.gmail.com/
> [4] https://lore.kernel.org/linux-nvdimm/20200903160608.GU878166@iweiny-DESK2.sc.intel.com/
> 
> Fixes: 6180bb446ab6 ("dax: fix detection of dax support for non-persistent memory block devices")
> Reported-by: Yi Zhang <yi.zhang@...hat.com>
> Reported-by: Mikulas Patocka <mpatocka@...hat.com>
> Signed-off-by: Adrian Huang <ahuang12@...ovo.com>
> Reviewed-by: Jan Kara <jack@...e.cz>
> Cc: Coly Li <colyli@...e.de>
> Cc: Ira Weiny <ira.weiny@...el.com>
> Cc: John Pittman <jpittman@...hat.com>

Although I see that this is fix is already applied but ccing fsdevel and
ext4 since I ended up debugging and coming to the same conclusion as
this patch is fixing the recursion loop.
If not already applied then feel free to add:

Tested-by: Ritesh Harjani <riteshh@...ux.ibm.com>


> ---
> Changelog:
> v3:
>      1. Add Reviewed-by from Jan
>      2. Add Reported-by
>      3. Replace lists.01.org with lore.kernel
> v2:
>      Remove the checking for the returned value '-EOPNOTSUPP' of
>      dax_direct_access(). Jan has prepared a patch to address the
>      issue in dm.
> ---
>   drivers/dax/super.c | 12 ++++++------
>   1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/dax/super.c b/drivers/dax/super.c
> index e5767c83ea23..11d0541e6f8f 100644
> --- a/drivers/dax/super.c
> +++ b/drivers/dax/super.c
> @@ -85,6 +85,12 @@ bool __generic_fsdax_supported(struct dax_device *dax_dev,
>   		return false;
>   	}
>   
> +	if (!dax_dev) {
> +		pr_debug("%s: error: dax unsupported by block device\n",
> +				bdevname(bdev, buf));
> +		return false;
> +	}
> +
>   	err = bdev_dax_pgoff(bdev, start, PAGE_SIZE, &pgoff);
>   	if (err) {
>   		pr_info("%s: error: unaligned partition for dax\n",
> @@ -100,12 +106,6 @@ bool __generic_fsdax_supported(struct dax_device *dax_dev,
>   		return false;
>   	}
>   
> -	if (!dax_dev || !bdev_dax_supported(bdev, blocksize)) {
> -		pr_debug("%s: error: dax unsupported by block device\n",
> -				bdevname(bdev, buf));
> -		return false;
> -	}
> -
>   	id = dax_read_lock();
>   	len = dax_direct_access(dax_dev, pgoff, 1, &kaddr, &pfn);
>   	len2 = dax_direct_access(dax_dev, pgoff_end, 1, &end_kaddr, &end_pfn);
>