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    SubjectRe: [PATCH 3/4] threadgroup: extend threadgroup_lock() to cover exit and exec
    On Sun, Sep 4, 2011 at 11:01 AM, Tejun Heo <htejun@gmail.com> wrote:
    > From: Tejun Heo <tj@kernel.org>
    >
    > threadgroup_lock() protected only protected against new addition to
    > the threadgroup, which was inherently somewhat incomplete and
    > problematic for its only user cgroup.  On-going migration could race
    > against exec and exit leading to interesting problems - the symmetry
    > between various attach methods, task exiting during method execution,
    > ->exit() racing against attach methods, migrating task switching basic
    > properties during exec and so on.
    >
    > This patch extends threadgroup_lock() such that it protects against
    > all three threadgroup altering operations - fork, exit and exec.  For
    > exit, threadgroup_change_begin/end() calls are added to exit path.
    > For exec, threadgroup_[un]lock() are updated to also grab and release
    > cred_guard_mutex.

    Can you add a comment (either in the commit or in the code) about why
    the cred_guard_mutex change is necessary? Is it simply that exec takes
    cred_guard_mutex and hence this excludes exec, or is there something
    more subtle?

    Paul
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