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SubjectRe: [000/136] review
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 <>
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 <>
Cc: KAMEZAWA Hiroyuki <>
Cc: Balbir Singh <>
Cc: Hugh Dickins <>
Cc: Johannes Weiner <>
Signed-off-by: Andrew Morton <>
Signed-off-by: Linus Torvalds <>

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).

Daisuke Nishimura.

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