linux-kernel - Re: [lkp-robot] [btrfs] beeeccca9b: WARNING:at_mm/util.c:#kvmalloc

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Message-ID: <20170531145848.GB12135@suse.cz>
Date:   Wed, 31 May 2017 16:58:48 +0200
From:   David Sterba <dsterba@...e.cz>
To:     Omar Sandoval <osandov@...ndov.com>
Cc:     Michal Hocko <mhocko@...nel.org>, lkp@...org,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Omar Sandoval <osandov@...com>, Vinnie Magro <vmagro@...com>,
        kernel test robot <xiaolong.ye@...el.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [lkp-robot] [btrfs]  beeeccca9b:
 WARNING:at_mm/util.c:#kvmalloc_node

On Wed, May 31, 2017 at 02:29:20AM -0700, Omar Sandoval wrote:
> diff --git a/fs/btrfs/free-space-tree.c b/fs/btrfs/free-space-tree.c
> index fc0bd8406758..5abd3cd71144 100644
> --- a/fs/btrfs/free-space-tree.c
> +++ b/fs/btrfs/free-space-tree.c
> @@ -153,21 +153,18 @@ static inline u32 free_space_bitmap_size(u64 size, u32 sectorsize)
>  
>  static u8 *alloc_bitmap(u32 bitmap_size)
>  {
> -	void *mem;
> +	u8 *ret;
> +	unsigned int nofs_flag;
>  
>  	/*
> -	 * The allocation size varies, observed numbers were < 4K up to 16K.
> -	 * Using vmalloc unconditionally would be too heavy, we'll try
> -	 * contiguous allocations first.
> +	 * GFP_NOFS doesn't work with kvmalloc(), but we really can't recurse
> +	 * into the filesystem as the free space bitmap can be modified in the
> +	 * critical section of a transaction commit.
>  	 */
> -	if  (bitmap_size <= PAGE_SIZE)
> -		return kzalloc(bitmap_size, GFP_NOFS);
> -
> -	mem = kzalloc(bitmap_size, GFP_NOFS | __GFP_NOWARN);
> -	if (mem)
> -		return mem;
> -
> -	return __vmalloc(bitmap_size, GFP_NOFS | __GFP_ZERO, PAGE_KERNEL);
> +	nofs_flag = memalloc_nofs_save();
> +	ret = kvmalloc(bitmap_size, GFP_KERNEL);
> +	memalloc_nofs_restore(nofs_flag);
> +	return ret;
>  }
>  
>  int convert_free_space_to_bitmaps(struct btrfs_trans_handle *trans,
> 
> Dave, would you prefer to replace the patch we have now or do an
> incremental patch on top of it?

I'll drop the patch "btrfs: Use kvzalloc instead of kzalloc/vmalloc in
alloc_bitmap", please send an updated version.