[PATCH rc7-mm1] fix BUG at mm/swap.c:405!

Hugh Dickins
2007-09-24T13:18:20Z

a.k.a. mm-use-pagevec-to-rotate-reclaimable-page-fix-2.patch

rotate_reclaimable_page() is not necessarily called with IRQ disabled:
it must do so when calling the helpfully commented pagevec_move_tail().

Hmm, if pagevec_move_tail() is assuming IRQ disabled, why should it
bother with irqsave/irqrestore variants of spin_lock? Because we like
to see them on lru_lock? But vmscan.c already has one bare spin_lock().

Signed-off-by: Hugh Dickins <hugh@veritas.com>
---

mm/swap.c | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)

--- 2.6.23-rc7-mm1/mm/swap.c 2007-09-24 11:05:55.000000000 +0100
+++ linux/mm/swap.c 2007-09-24 13:08:12.000000000 +0100
@@ -102,7 +102,6 @@ static void pagevec_move_tail(struct pag
int i;
int pgmoved = 0;
struct zone *zone = NULL;
- unsigned long uninitialized_var(flags);

for (i = 0; i < pagevec_count(pvec); i++) {
struct page *page = pvec->pages[i];
@@ -110,9 +109,9 @@ static void pagevec_move_tail(struct pag

if (pagezone != zone) {
if (zone)
- spin_unlock_irqrestore(&zone->lru_lock, flags);
+ spin_unlock(&zone->lru_lock);
zone = pagezone;
- spin_lock_irqsave(&zone->lru_lock, flags);
+ spin_lock(&zone->lru_lock);
}
if (PageLRU(page) && !PageActive(page)) {
list_move_tail(&page->lru, &zone->inactive_list);
@@ -120,7 +119,7 @@ static void pagevec_move_tail(struct pag
}
}
if (zone)
- spin_unlock_irqrestore(&zone->lru_lock, flags);
+ spin_unlock(&zone->lru_lock);
__count_vm_events(PGROTATED, pgmoved);
release_pages(pvec->pages, pvec->nr, pvec->cold);
pagevec_reinit(pvec);
@@ -150,6 +149,7 @@ void move_tail_pages()
int rotate_reclaimable_page(struct page *page)
{
struct pagevec *pvec;
+ unsigned long flags;

if (PageLocked(page))
return 1;
@@ -162,9 +162,11 @@ int rotate_reclaimable_page(struct page

if (PageLRU(page) && !PageActive(page)) {
page_cache_get(page);
+ local_irq_save(flags);
pvec = &__get_cpu_var(rotate_pvecs);
if (!pagevec_add(pvec, page))
pagevec_move_tail(pvec);
+ local_irq_restore(flags);
}
if (!test_clear_page_writeback(page))
BUG();