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    SubjectRe: [PATCH] mm: initialize variable for mem_cgroup_end_page_stat
    On Thu, Oct 30, 2014 at 09:32:14AM -0400, Sasha Levin wrote:
    > 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.

    We are not using that value anywhere if !memcg. What path are you
    referring to?

    > Yes, it's a compiler warning.

    Could you provide that please, including arch, and gcc version?

    Thanks


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