linux-kernel - Re: [PATCH] zram: Using GFP_ATOMIC instead of GFP_KERNEL to allocate bitmap memory in backing_dev

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Date:   Thu, 30 Nov 2023 08:37:40 -0700
From:   Jens Axboe <axboe@...nel.dk>
To:     Dongyun Liu <dongyun.liu3@...il.com>, minchan@...nel.org,
        senozhatsky@...omium.org
Cc:     linux-kernel@...r.kernel.org, linux-block@...r.kernel.org,
        lincheng.yang@...nssion.com, jiajun.ling@...nssion.com,
        ldys2014@...mail.com, Dongyun Liu <dongyun.liu@...nssion.com>
Subject: Re: [PATCH] zram: Using GFP_ATOMIC instead of GFP_KERNEL to allocate
 bitmap memory in backing_dev_store

On 11/30/23 8:20 AM, Dongyun Liu wrote:
> diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> index d77d3664ca08..ee6c22c50e09 100644
> --- a/drivers/block/zram/zram_drv.c
> +++ b/drivers/block/zram/zram_drv.c
> @@ -514,7 +514,7 @@ static ssize_t backing_dev_store(struct device *dev,
>  
>  	nr_pages = i_size_read(inode) >> PAGE_SHIFT;
>  	bitmap_sz = BITS_TO_LONGS(nr_pages) * sizeof(long);
> -	bitmap = kvzalloc(bitmap_sz, GFP_KERNEL);
> +	bitmap = kmalloc(bitmap_sz, GFP_ATOMIC);
>  	if (!bitmap) {
>  		err = -ENOMEM;
>  		goto out;

Outside of this moving from a zeroed alloc to one that does not, the
change looks woefully incomplete. Why does this allocation need to be
GFP_ATOMIC, and:

1) file_name = kmalloc(PATH_MAX, GFP_KERNEL); does not
2) filp_open() -> getname_kernel() -> __getname() does not
3) filp_open() -> getname_kernel() does not
4) bdev_open_by_dev() does not

IOW, you have a slew of GFP_KERNEL allocations in there, and you
probably just patched the largest one. But the core issue remains.

The whole handling of backing_dev_store() looks pretty broken.

-- 
Jens Axboe