Re: [000/136] 2.6.31.2-stable review

[Daisuke Nishimura]

Hi, Greg.

Could you consider adding the following commit in linus-tree to 2.6.31-stable ?
I've verified the commit can be applied onto v2.6.31.2.


commit 31a5639623a487d6db996c8138c9e53fef2e2d91
Author: Daisuke Nishimura <nishimura@xxxxxxxxxxxxxxxxx>
Date:   Mon Sep 21 17:02:50 2009 -0700

    mm: add_to_swap_cache() must not sleep

    After commit 355cfa73 ("mm: modify swap_map and add SWAP_HAS_CACHE flag"),
    read_swap_cache_async() will busy-wait while a entry doesn't exist in swap
    cache but it has SWAP_HAS_CACHE flag.

    Such entries can exist on add/delete path of swap cache.  On add path,
    add_to_swap_cache() is called soon after SWAP_HAS_CACHE flag is set, and
    on delete path, swapcache_free() will be called (SWAP_HAS_CACHE flag is
    cleared) soon after __delete_from_swap_cache() is called.  So, the
    busy-wait works well in most cases.

    But this mechanism can cause soft lockup if add_to_swap_cache() sleeps and
    read_swap_cache_async() tries to swap-in the same entry on the same cpu.

    This patch calls radix_tree_preload() before swapcache_prepare() and
    divides add_to_swap_cache() into two part: radix_tree_preload() part and
    radix_tree_insert() part(define it as __add_to_swap_cache()).

    Signed-off-by: Daisuke Nishimura <nishimura@xxxxxxxxxxxxxxxxx>
    Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
    Cc: Balbir Singh <balbir@xxxxxxxxxxxxxxxxxx>
    Cc: Hugh Dickins <hugh.dickins@xxxxxxxxxxxxx>
    Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
    Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
    Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>


This is a fix for a soft lockup bug introduced at 2.6.31-rc1.

It was rare, but I saw the bug several times, and Alok-san reported me the bug
also happens on Ubuntu 9.10(alpha).

  https://bugs.launchpad.net/ubuntu/+source/linux/+bug/433646


Thanks,
Daisuke Nishimura.
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