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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@mxp.nes.nec.co.jp>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
hifive-unleashed-5.1
Daisuke Nishimura 2009-09-21 17:02:50 -07:00 committed by Linus Torvalds
parent 8fbb398f5c
commit 31a5639623
1 changed files with 46 additions and 24 deletions
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70
mm/swap_state.c
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@ -67,10 +67,10 @@ void show_swap_cache_info(void)
} }
/* /*
* add_to_swap_cache resembles add_to_page_cache_locked on swapper_space, * __add_to_swap_cache resembles add_to_page_cache_locked on swapper_space,
* but sets SwapCache flag and private instead of mapping and index. * but sets SwapCache flag and private instead of mapping and index.
*/ */
int add_to_swap_cache(struct page *page, swp_entry_t entry, gfp_t gfp_mask) static int __add_to_swap_cache(struct page *page, swp_entry_t entry)
{ {
int error; int error;
@ -78,28 +78,37 @@ int add_to_swap_cache(struct page *page, swp_entry_t entry, gfp_t gfp_mask)
VM_BUG_ON(PageSwapCache(page)); VM_BUG_ON(PageSwapCache(page));
VM_BUG_ON(!PageSwapBacked(page)); VM_BUG_ON(!PageSwapBacked(page));
page_cache_get(page);
SetPageSwapCache(page);
set_page_private(page, entry.val);
spin_lock_irq(&swapper_space.tree_lock);
error = radix_tree_insert(&swapper_space.page_tree, entry.val, page);
if (likely(!error)) {
total_swapcache_pages++;
__inc_zone_page_state(page, NR_FILE_PAGES);
INC_CACHE_INFO(add_total);
}
spin_unlock_irq(&swapper_space.tree_lock);
if (unlikely(error)) {
set_page_private(page, 0UL);
ClearPageSwapCache(page);
page_cache_release(page);
}
return error;
}
int add_to_swap_cache(struct page *page, swp_entry_t entry, gfp_t gfp_mask)
{
int error;
error = radix_tree_preload(gfp_mask); error = radix_tree_preload(gfp_mask);
if (!error) { if (!error) {
page_cache_get(page); error = __add_to_swap_cache(page, entry);
SetPageSwapCache(page);
set_page_private(page, entry.val);
spin_lock_irq(&swapper_space.tree_lock);
error = radix_tree_insert(&swapper_space.page_tree,
entry.val, page);
if (likely(!error)) {
total_swapcache_pages++;
__inc_zone_page_state(page, NR_FILE_PAGES);
INC_CACHE_INFO(add_total);
}
spin_unlock_irq(&swapper_space.tree_lock);
radix_tree_preload_end(); radix_tree_preload_end();
if (unlikely(error)) {
set_page_private(page, 0UL);
ClearPageSwapCache(page);
page_cache_release(page);
}
} }
return error; return error;
} }
@ -289,14 +298,25 @@ struct page *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
break; /* Out of memory */ break; /* Out of memory */
} }
/*
* call radix_tree_preload() while we can wait.
*/
err = radix_tree_preload(gfp_mask & GFP_KERNEL);
if (err)
break;
/* /*
* Swap entry may have been freed since our caller observed it. * Swap entry may have been freed since our caller observed it.
*/ */
err = swapcache_prepare(entry); err = swapcache_prepare(entry);
if (err == -EEXIST) /* seems racy */ if (err == -EEXIST) { /* seems racy */
radix_tree_preload_end();
continue; continue;
if (err) /* swp entry is obsolete ? */ }
if (err) { /* swp entry is obsolete ? */
radix_tree_preload_end();
break; break;
}
/* /*
* Associate the page with swap entry in the swap cache. * Associate the page with swap entry in the swap cache.
@ -308,8 +328,9 @@ struct page *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
*/ */
__set_page_locked(new_page); __set_page_locked(new_page);
SetPageSwapBacked(new_page); SetPageSwapBacked(new_page);
err = add_to_swap_cache(new_page, entry, gfp_mask & GFP_KERNEL); err = __add_to_swap_cache(new_page, entry);
if (likely(!err)) { if (likely(!err)) {
radix_tree_preload_end();
/* /*
* Initiate read into locked page and return. * Initiate read into locked page and return.
*/ */
@ -317,6 +338,7 @@ struct page *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
swap_readpage(new_page); swap_readpage(new_page);
return new_page; return new_page;
} }
radix_tree_preload_end();
ClearPageSwapBacked(new_page); ClearPageSwapBacked(new_page);
__clear_page_locked(new_page); __clear_page_locked(new_page);
swapcache_free(entry, NULL); swapcache_free(entry, NULL);