linux-kernel - Re: [PATCH] f2fs: fix to relocate f2fs_balance

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Message-ID: <20191206040823.GA33758@jaegeuk-macbookpro.roam.corp.google.com>
Date:   Thu, 5 Dec 2019 20:08:23 -0800
From:   Jaegeuk Kim <jaegeuk@...nel.org>
To:     Chao Yu <yuchao0@...wei.com>
Cc:     linux-f2fs-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org, chao@...nel.org
Subject: Re: [PATCH] f2fs: fix to relocate f2fs_balance_fs() in mkwrite()

Hi Chao,

I was testing this.

https://github.com/jaegeuk/f2fs/commit/76be33b9f1fce70dd2d3f04f66d0f78b418fe3f5

On 12/06, Chao Yu wrote:
> As Dinosaur Huang reported, there is a potential deadlock in between
> GC and mkwrite():
> 
> Thread A			Thread B
> - do_page_mkwrite
>  - f2fs_vm_page_mkwrite
>   - lock_page
> 				- f2fs_balance_fs
>                                  - mutex_lock(gc_mutex)
> 				 - f2fs_gc
> 				  - do_garbage_collect
> 				   - ra_data_block
> 				    - grab_cache_page
>   - f2fs_balance_fs
>    - mutex_lock(gc_mutex)
> 
> In order to fix this, we just move f2fs_balance_fs() out of page lock's
> coverage in f2fs_vm_page_mkwrite().
> 
> Reported-by: Dinosaur Huang <dinosaur.huang@...soc.com>
> Signed-off-by: Chao Yu <yuchao0@...wei.com>
> ---
>  fs/f2fs/file.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
> index c0560d62dbee..ed3290225506 100644
> --- a/fs/f2fs/file.c
> +++ b/fs/f2fs/file.c
> @@ -67,6 +67,8 @@ static vm_fault_t f2fs_vm_page_mkwrite(struct vm_fault *vmf)
>  
>  	f2fs_bug_on(sbi, f2fs_has_inline_data(inode));
>  
> +	f2fs_balance_fs(sbi, true);
> +
>  	file_update_time(vmf->vma->vm_file);
>  	down_read(&F2FS_I(inode)->i_mmap_sem);
>  	lock_page(page);
> @@ -120,8 +122,6 @@ static vm_fault_t f2fs_vm_page_mkwrite(struct vm_fault *vmf)
>  out_sem:
>  	up_read(&F2FS_I(inode)->i_mmap_sem);
>  
> -	f2fs_balance_fs(sbi, dn.node_changed);
> -
>  	sb_end_pagefault(inode->i_sb);
>  err:
>  	return block_page_mkwrite_return(err);
> -- 
> 2.18.0.rc1