linux-kernel - Re: [f2fs-dev] [PATCH v2] f2fs: avoid cpu lockup

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Date:   Mon, 17 Jul 2017 15:38:58 -0700
From:   Jaegeuk Kim <jaegeuk@...nel.org>
To:     Chao Yu <chao@...nel.org>
Cc:     linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net
Subject: Re: [f2fs-dev] [PATCH v2] f2fs: avoid cpu lockup

On 07/17, Chao Yu wrote:
> On 2017/7/16 9:04, Jaegeuk Kim wrote:
> > Before retrying to flush data or dentry pages, we need to release cpu in order
> > to prevent watchdog.
> > 
> > Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
> 
> Reviewed-by: Chao Yu <yuchao0@...wei.com>
> 
> > ---
> > Change log from v1:
> >  - timeout more specifically
> > 
> >  fs/f2fs/checkpoint.c | 10 ++++++++++
> >  1 file changed, 10 insertions(+)
> > 
> > diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
> > index 56bbf592e487..5b876f6d3f6b 100644
> > --- a/fs/f2fs/checkpoint.c
> > +++ b/fs/f2fs/checkpoint.c
> > @@ -879,6 +879,7 @@ int sync_dirty_inodes(struct f2fs_sb_info *sbi, enum inode_type type)
> >  	struct inode *inode;
> >  	struct f2fs_inode_info *fi;
> >  	bool is_dir = (type == DIR_INODE);
> > +	unsigned long ino = 0;
> >  
> >  	trace_f2fs_sync_dirty_inodes_enter(sbi->sb, is_dir,
> >  				get_pages(sbi, is_dir ?
> > @@ -901,8 +902,17 @@ int sync_dirty_inodes(struct f2fs_sb_info *sbi, enum inode_type type)
> >  	inode = igrab(&fi->vfs_inode);
> >  	spin_unlock(&sbi->inode_lock[type]);
> >  	if (inode) {
> > +		unsigned long cur_ino = inode->i_ino;
> > +
> >  		filemap_fdatawrite(inode->i_mapping);
> >  		iput(inode);
> > +		/* We need to give cpu to another writers. */
> > +		if (ino == cur_ino) {
> 
> We failed to flush dirty pages of inode due to encountering -EAGAIN of writepage?

Actually, I found this from a bug case in experimental patches which just skips
it accidently. I think WB_SYNC_ALL doesn't return EAGAIN.

Thanks,

> 
> Thanks,
> 
> > +			congestion_wait(BLK_RW_ASYNC, HZ/50);
> > +			cond_resched();
> > +		} else {
> > +			ino = cur_ino;
> > +		}
> >  	} else {
> >  		/*
> >  		 * We should submit bio, since it exists several
> >