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    Subject[PATCH 7/8] x86, mce: rework use of TIF_MCE_NOTIFY
    The basic flow of MCE handler is summarized as follows:
    1) from NMI context:
    check hardware error registers, determine error severity,
    and then panic or request non-NMI context by irq_work() to
    continue the system.
    2) from (irq) context:
    call non-NMI safe functions,
    wake up loggers and schedule work if required
    3) from worker thread:
    process some time-consuming works like memory poisoning.

    TIF_MCE_NOTIFY flag is relatively legacy and have used to do tasks of
    2) and 3) on the thread context that interrupted by MCE. However now
    use of irq_work() and work-queue is enough for these tasks, so this
    patch removes duplicated tasks in mce_notify_process().

    As the result there is no task to be done in the interrupted context,
    but soon if SRAR is supported there would be some thread-specific thing
    for action required. So (even if it will be removed soon) keep the flag
    for such possible future use, until better mechanism is introduced.

    Signed-off-by: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>
    ---
    arch/x86/kernel/cpu/mcheck/mce.c | 28 ++++++++++++----------------
    1 files changed, 12 insertions(+), 16 deletions(-)

    diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
    index a118496..bc8a02c 100644
    --- a/arch/x86/kernel/cpu/mcheck/mce.c
    +++ b/arch/x86/kernel/cpu/mcheck/mce.c
    @@ -1053,8 +1053,9 @@ void do_machine_check(struct pt_regs *regs, long error_code)
    if (kill_it && tolerant < 3)
    force_sig(SIGBUS, current);

    - /* notify userspace ASAP */
    - set_thread_flag(TIF_MCE_NOTIFY);
    + /* Trap this thread before returning to user, for action required */
    + if (worst == MCE_AR_SEVERITY)
    + set_thread_flag(TIF_MCE_NOTIFY);

    if (worst > 0)
    mce_report_event(regs);
    @@ -1066,25 +1067,22 @@ out:
    EXPORT_SYMBOL_GPL(do_machine_check);

    /*
    - * Called after mce notification in process context. This code
    - * is allowed to sleep. Call the high level VM handler to process
    - * any corrupted pages.
    - * Assume that the work queue code only calls this one at a time
    - * per CPU.
    - * Note we don't disable preemption, so this code might run on the wrong
    - * CPU. In this case the event is picked up by the scheduled work queue.
    - * This is merely a fast path to expedite processing in some common
    - * cases.
    + * Called in process context that interrupted by MCE and marked with
    + * TIF_MCE_NOTFY, just before returning to erroneous userland.
    + * This code is allowed to sleep.
    + * Attempt possible recovery such as calling the high level VM handler to
    + * process any corrupted pages, and kill/signal current process if required.
    */
    void mce_notify_process(void)
    {
    - mce_notify_irq();
    - mce_memory_failure_process();
    + clear_thread_flag(TIF_MCE_NOTIFY);
    +
    + /* TBD: do recovery for action required event */
    }

    static void mce_process_work(struct work_struct *dummy)
    {
    - mce_notify_process();
    + mce_memory_failure_process();
    }

    #ifdef CONFIG_X86_MCE_INTEL
    @@ -1187,8 +1185,6 @@ int mce_notify_irq(void)
    /* Not more than two messages every minute */
    static DEFINE_RATELIMIT_STATE(ratelimit, 60*HZ, 2);

    - clear_thread_flag(TIF_MCE_NOTIFY);
    -
    if (test_and_clear_bit(0, &mce_need_notify)) {
    /* wake processes polling /dev/mcelog */
    wake_up_interruptible(&mce_chrdev_wait);
    --
    1.7.1



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