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    SubjectRe: [RFC PATCH 1/2] Fix PF_NOFREEZE and freezeable race
    On 04/19, Rafael J. Wysocki wrote:
    >
    > On Thursday, 19 April 2007 14:02, Gautham R Shenoy wrote:
    > > This patch fixes the race pointed out by Oleg Nesterov.
    > >
    > > * Freezer marks a thread as freezeable.
    > > * The thread now marks itself PF_NOFREEZE causing it to
    > > freeze on calling try_to_freeze(). Thus the task is frozen, even though
    > > it doesn't want to.
    > > * Subsequent thaw_processes() will also fail to thaw the task since it is
    > > marked PF_NOFREEZE.
    > >
    > > Avoid this problem by checking the current task's PF_NOFREEZE status in the
    > > refrigerator before marking current as frozen.
    > >
    > > Signed-off-by: Gautham R Shenoy <ego@in.ibm.com>
    >
    > Looks good, although I'm not sure if we don't need to call recalc_sigpending()
    > for tasks that turn out to be PF_NOFREEZE.

    I agree, we should clear TIF_SIGPENDING. It is not so critical for user-space
    tasks, but for the kernel thread it may remain pending forever, causing subtle
    failures.

    Gautham, isn't it possible to make a more simpler patch ? Just add PF_NOFREEZE
    check to frozen_process,

    static inline void frozen_process(struct task_struct *p)
    {
    if (!unlikely(current->flags & PF_NOFREEZE)) {
    p->flags |= PF_FROZEN;
    wmb();
    }
    clear_tsk_thread_flag(p, TIF_FREEZE);
    }

    No?

    Oleg.

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