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On Tue, Nov 02, 2010 at 07:45:36PM +0100, Christoph Hellwig wrote:
> iprune_sem is continously giving us lockdep warnings because we do take it in
> read mode in the reclaim path, but we're also doing non-NOFS allocations under
> it taken in write mode.
>
> Taking a bit deeper look at it I think it's fixable quite trivially:
>
> - for invalidate_inodes we do not need iprune_sem at all. We have an active
> reference on the superblock, so the filesystem is not going away until it
> has finished.
> - for evict_inodes we do need it, to make sure prune_icache has done it's
> work before we tear down the superblock. But there is no reason to
> hold it over the actual reclaim operation - it's enough to cycle through
> it after the actual reclaim to make sure we wait for any pending
> prune_icache to complete.
>
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>
>
> diff --git a/fs/inode.c b/fs/inode.c
> index ae2727a..cfa7722 100644
> --- a/fs/inode.c
> +++ b/fs/inode.c
> @@ -492,8 +492,6 @@ void evict_inodes(struct super_block *sb)
> struct inode *inode, *next;
> LIST_HEAD(dispose);
>
> - down_write(&iprune_sem);
> -
> spin_lock(&inode_lock);
> list_for_each_entry_safe(inode, next, &sb->s_inodes, i_sb_list) {
> if (atomic_read(&inode->i_count))
> @@ -518,6 +516,13 @@ void evict_inodes(struct super_block *sb)
> spin_unlock(&inode_lock);
>
> dispose_list(&dispose);
> +
> + /*
> + * Cycle through iprune_sem to make sure any inode that prune_icache
> + * moved off the list before we took the lock has been fully torn
> + * down.
> + */
> + down_write(&iprune_sem);
> up_write(&iprune_sem);
> }
>
> @@ -534,8 +539,6 @@ int invalidate_inodes(struct super_block *sb)
> struct inode *inode, *next;
> LIST_HEAD(dispose);
>
> - down_write(&iprune_sem);
> -
> spin_lock(&inode_lock);
> list_for_each_entry_safe(inode, next, &sb->s_inodes, i_sb_list) {
> if (inode->i_state & (I_NEW | I_FREEING | I_WILL_FREE))
> @@ -559,7 +562,6 @@ int invalidate_inodes(struct super_block *sb)
> spin_unlock(&inode_lock);
>
> dispose_list(&dispose);
> - up_write(&iprune_sem);
>
> return busy;
> }
---end quoted text---
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