linux-kernel - Re: [PATCH 3/4] f2fs: fix avoid race between truncate and background GC

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Message-ID: <20180729061351.GA5102@jaegeuk-macbookpro.roam.corp.google.com>
Date:   Sat, 28 Jul 2018 23:13:51 -0700
From:   Jaegeuk Kim <jaegeuk@...nel.org>
To:     Chao Yu <chao@...nel.org>
Cc:     Chao Yu <yuchao0@...wei.com>,
        linux-f2fs-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/4] f2fs: fix avoid race between truncate and background
 GC

On 07/29, Chao Yu wrote:
> On 2018/7/29 9:58, Jaegeuk Kim wrote:
> > On 07/27, Chao Yu wrote:
> >> Thread A				Background GC
> >> - f2fs_setattr isize to 0
> >>  - truncate_setsize
> >> 					- gc_data_segment
> >> 					 - f2fs_get_read_data_page page #0
> >> 					  - set_page_dirty
> >> 					  - set_cold_data
> >>  - f2fs_truncate
> >>
> >> - f2fs_setattr isize to 4k
> >> - read 4k <--- hit data in cached page #0
> >>
> >> Above race condition can cause read out invalid data in a truncated
> >> page, fix it by i_gc_rwsem[WRITE] lock.
> > 
> > We can truncate pages again after f2fs_truncate()?
> 
> I think it can fix this issue, although it looks a little strange to truncate
> page cache twice.

It'd be fine to do setsize first, and drop the cache later.

> 
> Thanks,
> 
> > 
> >>
> >> Signed-off-by: Chao Yu <yuchao0@...wei.com>
> >> ---
> >>  fs/f2fs/data.c |  4 ++++
> >>  fs/f2fs/file.c | 33 +++++++++++++++++++--------------
> >>  2 files changed, 23 insertions(+), 14 deletions(-)
> >>
> >> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> >> index 071224ded5f4..a29f3162b887 100644
> >> --- a/fs/f2fs/data.c
> >> +++ b/fs/f2fs/data.c
> >> @@ -2214,10 +2214,14 @@ static void f2fs_write_failed(struct address_space *mapping, loff_t to)
> >>  	loff_t i_size = i_size_read(inode);
> >>  
> >>  	if (to > i_size) {
> >> +		down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
> >>  		down_write(&F2FS_I(inode)->i_mmap_sem);
> >> +
> >>  		truncate_pagecache(inode, i_size);
> >>  		f2fs_truncate_blocks(inode, i_size, true);
> >> +
> >>  		up_write(&F2FS_I(inode)->i_mmap_sem);
> >> +		up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
> >>  	}
> >>  }
> >>  
> >> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
> >> index 7bd2412a8c37..ed5c9b0e0d0c 100644
> >> --- a/fs/f2fs/file.c
> >> +++ b/fs/f2fs/file.c
> >> @@ -796,22 +796,25 @@ int f2fs_setattr(struct dentry *dentry, struct iattr *attr)
> >>  	}
> >>  
> >>  	if (attr->ia_valid & ATTR_SIZE) {
> >> -		if (attr->ia_size <= i_size_read(inode)) {
> >> -			down_write(&F2FS_I(inode)->i_mmap_sem);
> >> -			truncate_setsize(inode, attr->ia_size);
> >> +		bool to_smaller = (attr->ia_size <= i_size_read(inode));
> >> +
> >> +		down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
> >> +		down_write(&F2FS_I(inode)->i_mmap_sem);
> >> +
> >> +		truncate_setsize(inode, attr->ia_size);
> >> +
> >> +		if (to_smaller)
> >>  			err = f2fs_truncate(inode);
> >> -			up_write(&F2FS_I(inode)->i_mmap_sem);
> >> -			if (err)
> >> -				return err;
> >> -		} else {
> >> -			/*
> >> -			 * do not trim all blocks after i_size if target size is
> >> -			 * larger than i_size.
> >> -			 */
> >> -			down_write(&F2FS_I(inode)->i_mmap_sem);
> >> -			truncate_setsize(inode, attr->ia_size);
> >> -			up_write(&F2FS_I(inode)->i_mmap_sem);
> >> +		/*
> >> +		 * do not trim all blocks after i_size if target size is
> >> +		 * larger than i_size.
> >> +		 */
> >> +		up_write(&F2FS_I(inode)->i_mmap_sem);
> >> +		up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
> >> +		if (err)
> >> +			return err;
> >>  
> >> +		if (!to_smaller) {
> >>  			/* should convert inline inode here */
> >>  			if (!f2fs_may_inline_data(inode)) {
> >>  				err = f2fs_convert_inline_inode(inode);
> >> @@ -958,6 +961,7 @@ static int punch_hole(struct inode *inode, loff_t offset, loff_t len)
> >>  
> >>  			blk_start = (loff_t)pg_start << PAGE_SHIFT;
> >>  			blk_end = (loff_t)pg_end << PAGE_SHIFT;
> >> +			down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
> >>  			down_write(&F2FS_I(inode)->i_mmap_sem);
> >>  			truncate_inode_pages_range(mapping, blk_start,
> >>  					blk_end - 1);
> >> @@ -966,6 +970,7 @@ static int punch_hole(struct inode *inode, loff_t offset, loff_t len)
> >>  			ret = f2fs_truncate_hole(inode, pg_start, pg_end);
> >>  			f2fs_unlock_op(sbi);
> >>  			up_write(&F2FS_I(inode)->i_mmap_sem);
> >> +			up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
> >>  		}
> >>  	}
> >>  
> >> -- 
> >> 2.18.0.rc1