Messages in this thread | | | Date | Thu, 30 Oct 2014 09:32:14 -0400 | From | Sasha Levin <> | Subject | Re: [PATCH] mm: initialize variable for mem_cgroup_end_page_stat |
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On 10/30/2014 04:27 AM, Michal Hocko wrote: > 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?
The problem is that you are attempting to read 'locked' when you call mem_cgroup_end_page_stat(), so it gets used even before you enter the function - and using uninitialized variables is undefined.
Yes, it's a compiler warning.
Thanks, Sasha
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