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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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