diff options
| author | Andrea Arcangeli <aarcange@redhat.com> | 2011-06-15 15:08:51 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2011-06-15 20:04:02 -0700 |
| commit | d179e84ba5da1d0024087d1759a2938817a00f3f (patch) | |
| tree | 169c9cc4030a793df1bc29613eff85ee3acef9a9 /mm/vmscan.c | |
| parent | 7454f4ba40b419eb999a3c61a99da662bf1a2bb8 (diff) | |
| download | lwn-d179e84ba5da1d0024087d1759a2938817a00f3f.tar.gz lwn-d179e84ba5da1d0024087d1759a2938817a00f3f.zip | |
mm: vmscan: do not use page_count without a page pin
It is unsafe to run page_count during the physical pfn scan because
compound_head could trip on a dangling pointer when reading
page->first_page if the compound page is being freed by another CPU.
[mgorman@suse.de: split out patch]
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Mel Gorman <mgorman@suse.de>
Reviewed-by: Michal Hocko <mhocko@suse.cz>
Reviewed-by: Minchan Kim <minchan.kim@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/vmscan.c')
| -rw-r--r-- | mm/vmscan.c | 16 |
1 files changed, 14 insertions, 2 deletions
diff --git a/mm/vmscan.c b/mm/vmscan.c index dbe6ea321df4..8ff834e19c24 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -1124,8 +1124,20 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan, nr_lumpy_dirty++; scan++; } else { - /* the page is freed already. */ - if (!page_count(cursor_page)) + /* + * Check if the page is freed already. + * + * We can't use page_count() as that + * requires compound_head and we don't + * have a pin on the page here. If a + * page is tail, we may or may not + * have isolated the head, so assume + * it's not free, it'd be tricky to + * track the head status without a + * page pin. + */ + if (!PageTail(cursor_page) && + !atomic_read(&cursor_page->_count)) continue; break; } |