Subject: Re: sk_lock: inconsistent {RECLAIM_FS-ON-W} -> {IN-RECLAIM_FS-W} usage

From: Wu Fengguang <[email-masked]>
Date: Mon, 8 Jun 2009 13:00:49 +0800

On Mon, Jun 08, 2009 at 12:55:18PM +0800, KOSAKI Motohiro wrote:
> Hi
> 
> > Hi,
> > 
> > This lockdep warning appears when doing stress memory tests over NFS.
> > 
> > page reclaim => nfs_writepage => tcp_sendmsg => lock sk_lock
> > 
> > tcp_close => lock sk_lock => tcp_send_fin => alloc_skb_fclone => page reclaim
> > 
> > Any ideas?
> 
> AFAIK, btrfs has re-dirty hack. 
> 
> ------------------------------------------------------------------
> static int btrfs_writepage(struct page *page, struct writeback_control *wbc)
> {
>         struct extent_io_tree *tree;
> 
> 
>         if (current->flags & PF_MEMALLOC) {
>                 redirty_page_for_writepage(wbc, page);
>                 unlock_page(page);
>                 return 0;
>         }
>         tree = &BTRFS_I(page->mapping->host)->io_tree;
>         return extent_write_full_page(tree, page, btrfs_get_extent, wbc);
> }
> ---------------------------------------------------------------
> 
> PF_MEMALLOC mean caller is try_to_free_pages(). (not normal write nor kswapd)
> Can't nfs does similar hack? 

But the trace shows that current is kswapd:

[ 1638.403414]  [<ffffffff811c9b69>] nfs_flush_one+0xb9/0x100
[ 1638.419417]  [<ffffffff811c3f82>] nfs_pageio_doio+0x32/0x70
[ 1638.419417]  [<ffffffff811c3fc9>] nfs_pageio_complete+0x9/0x10
[ 1638.427413]  [<ffffffff811c7ee5>] nfs_writepage_locked+0x85/0xc0
[ 1638.435414]  [<ffffffff811c8509>] nfs_writepage+0x19/0x40
[ 1638.435414]  [<ffffffff810ce005>] shrink_page_list+0x675/0x810
[ 1638.435414]  [<ffffffff810ce761>] shrink_list+0x301/0x650
[ 1638.435414]  [<ffffffff810ced23>] shrink_zone+0x273/0x370
[ 1638.435414]  [<ffffffff810cf9f9>] kswapd+0x729/0x7a0
[ 1638.435414]  [<ffffffff810666de>] kthread+0x9e/0xb0
[ 1638.435414]  [<ffffffff8100d0ca>] child_rip+0xa/0x20