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SubjectRe: [PATCH] vfs: Fix lock inversion in drop_pagecache_sb()
On Tue, Mar 25, 2008 at 07:12:27PM +0100, Jan Kara wrote:
> Fix longstanding lock inversion in drop_pagecache_sb by dropping inode_lock
> before calling __invalidate_mapping_pages(). We just have to make sure
> inode won't go away from under us by keeping reference to it and putting
> the reference only after we have safely resumed the scan of the inode
> list. A bit tricky but not too bad...

Reviewed-by: Fengguang Wu <wfg@mail.ustc.edu.cn>

It's a handy trick to iterate through the list_head :-)
I have practiced this in my filecache code, and it works nice.

Fengguang

> Signed-off-by: Jan Kara <jack@suse.cz>
> CC: Fengguang Wu <wfg@mail.ustc.edu.cn>
> CC: David Chinner <dgc@sgi.com>
>
> ---
> fs/drop_caches.c | 8 +++++++-
> 1 files changed, 7 insertions(+), 1 deletions(-)
>
> diff --git a/fs/drop_caches.c b/fs/drop_caches.c
> index 59375ef..f5aae26 100644
> --- a/fs/drop_caches.c
> +++ b/fs/drop_caches.c
> @@ -14,15 +14,21 @@ int sysctl_drop_caches;
>
> static void drop_pagecache_sb(struct super_block *sb)
> {
> - struct inode *inode;
> + struct inode *inode, *toput_inode = NULL;
>
> spin_lock(&inode_lock);
> list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {
> if (inode->i_state & (I_FREEING|I_WILL_FREE))
> continue;
> + __iget(inode);
> + spin_unlock(&inode_lock);
> __invalidate_mapping_pages(inode->i_mapping, 0, -1, true);
> + iput(toput_inode);
> + toput_inode = inode;
> + spin_lock(&inode_lock);
> }
> spin_unlock(&inode_lock);
> + iput(toput_inode);
> }
>
> void drop_pagecache(void)
> --
> 1.5.2.4
>



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