Messages in this thread | | | Date | Thu, 30 Oct 2014 09:27:12 +0100 | From | Michal Hocko <> | Subject | Re: [PATCH] mm: initialize variable for mem_cgroup_end_page_stat |
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On Wed 29-10-14 21:44:24, Sasha Levin wrote: > Commit "mm: memcontrol: fix missed end-writeback page accounting" has changed > the behaviour of mem_cgroup_begin_page_stat() to not always set the "locked" > parameter. > > We should initialize it at the callers to prevent garbage being used in a > later call to mem_cgroup_end_page_stat().
The contract is that if the returned memcg is non-NULL then the locked is always initialized. Nobody but mem_cgroup_end_page_stat should touch this variable and this function makes sure it uses it properly. Similar applies to flags which is initialized only if we really take the slow path (has a meaning only if locked == true).
So this is not really needed. Was this triggered by a compiler warning?
> Signed-off-by: Sasha Levin <sasha.levin@oracle.com> > --- > mm/page-writeback.c | 4 ++-- > mm/rmap.c | 4 ++-- > 2 files changed, 4 insertions(+), 4 deletions(-) > > diff --git a/mm/page-writeback.c b/mm/page-writeback.c > index 19ceae8..7a02c97 100644 > --- a/mm/page-writeback.c > +++ b/mm/page-writeback.c > @@ -2329,7 +2329,7 @@ int test_clear_page_writeback(struct page *page) > struct address_space *mapping = page_mapping(page); > unsigned long memcg_flags; > struct mem_cgroup *memcg; > - bool locked; > + bool locked = false; > int ret; > > memcg = mem_cgroup_begin_page_stat(page, &locked, &memcg_flags); > @@ -2366,7 +2366,7 @@ int __test_set_page_writeback(struct page *page, bool keep_write) > struct address_space *mapping = page_mapping(page); > unsigned long memcg_flags; > struct mem_cgroup *memcg; > - bool locked; > + bool locked = false; > int ret; > > memcg = mem_cgroup_begin_page_stat(page, &locked, &memcg_flags); > diff --git a/mm/rmap.c b/mm/rmap.c > index 19886fb..4a4dc84 100644 > --- a/mm/rmap.c > +++ b/mm/rmap.c > @@ -1044,7 +1044,7 @@ void page_add_file_rmap(struct page *page) > { > struct mem_cgroup *memcg; > unsigned long flags; > - bool locked; > + bool locked = false; > > memcg = mem_cgroup_begin_page_stat(page, &locked, &flags); > if (atomic_inc_and_test(&page->_mapcount)) { > @@ -1058,7 +1058,7 @@ static void page_remove_file_rmap(struct page *page) > { > struct mem_cgroup *memcg; > unsigned long flags; > - bool locked; > + bool locked = false; > > memcg = mem_cgroup_begin_page_stat(page, &locked, &flags); > > -- > 1.7.10.4 >
-- Michal Hocko SUSE Labs
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