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    Subject[PATCH 0/4] v6 Improve task->comm locking situation
    v6 tries to address the latest round of issues. Again, hopefully
    this is getting close to something that can be queued for 2.6.40.

    Since my commit 4614a696bd1c3a9af3a08f0e5874830a85b889d4, the
    current->comm value could be changed by other threads.

    This changed the comm locking rules, which previously allowed for
    unlocked current->comm access, since only the thread itself could
    change its comm.

    While this was brought up at the time, it was not considered
    problematic, as the comm writing was done in such a way that
    only null or incomplete comms could be read. However, recently
    folks have made it clear they want to see this issue resolved.

    So fair enough, as I opened this can of worms, I should work
    to resolve it and this patchset is my initial attempt.

    The proposed solution here is to introduce a new spinlock that
    exclusively protects the comm value. We use it to serialize
    access via get_task_comm() and set_task_comm(). Since some
    comm access is open-coded using the task lock, we preserve
    the task locking in set_task_comm for now. Once all comm
    access is converted to using get_task_comm, we can clean that
    up as well.

    I've also introduced a printk %ptc accessor, which makes the
    conversion to locked access simpler (as most uses are for printks)
    as well as a checkpatch rule to try to catch any new current->comm
    users from being introduced.

    New in this version: More tweaks to the checkpatch regex, and
    added a unlocked task->comm accessor for performance critical
    code paths that can handle the potential null or incomplete comm.

    Hopefully this will allow for a smooth transition, where we can
    slowly fix up the unlocked current->comm access bit by bit,
    reducing the race window with each patch, while not making the
    situation any worse then it was yesterday.

    Thanks for the comments and feedback so far.
    Any additional comments/feedback would still be appreciated.


    CC: Joe Perches <>
    CC: Ingo Molnar <>
    CC: Michal Nazarewicz <>
    CC: Andy Whitcroft <>
    CC: Jiri Slaby <>
    CC: KOSAKI Motohiro <>
    CC: David Rientjes <>
    CC: Dave Hansen <>
    CC: Andrew Morton <>

    John Stultz (4):
    comm: Introduce comm_lock spinlock to protect task->comm access
    comm: Add lock-free task->comm accessor
    printk: Add %ptc to safely print a task's comm Add check for task comm references

    fs/exec.c | 32 +++++++++++++++++++++++++++++---
    include/linux/init_task.h | 1 +
    include/linux/sched.h | 6 +++---
    kernel/fork.c | 1 +
    lib/vsprintf.c | 24 ++++++++++++++++++++++++
    scripts/ | 6 ++++++
    6 files changed, 64 insertions(+), 6 deletions(-)


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