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SubjectRe: [PATCH 5/6] x86, mce: handle "action required" errors (unjumbled version)
On Thu, Dec 15, 2011 at 04:22:25PM -0800, Tony Luck wrote:
> All non-urgent actions (reporting low severity errors and handling
> "action-optional" errors) are now handled by a work queue. This
> means that TIF_MCE_NOTIFY can be used to block execution for a
> thread experiencing an "action-required" fault until we get all
> cpus out of the machine check handler (and the thread that hit
> the fault into mce_notify_process().
>
> We use the new mce_{save,find,clear}_info() API to get information
> from do_machine_check() to mce_notify_process(), and then use the
> newly improved memory_failure(..., MF_ACTION_REQUIRED) to handle
> the error (possibly signalling the process).
>
> Update some comments to make the new code flows clearer.
>
> Signed-off-by: Tony Luck <tony.luck@intel.com>
> ---
>
> [Version posted earlier had the diff included in the commit comment,
> and then the real copy of the diff - making it hard to read. Sorry.]
>
> arch/x86/kernel/cpu/mcheck/mce.c | 71 ++++++++++++++++++++++++--------------
> 1 files changed, 45 insertions(+), 26 deletions(-)
>
> diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
> index 7d7303a..dfd20a6 100644
> --- a/arch/x86/kernel/cpu/mcheck/mce.c
> +++ b/arch/x86/kernel/cpu/mcheck/mce.c
> @@ -982,7 +982,9 @@ void do_machine_check(struct pt_regs *regs, long error_code)
> barrier();
>
> /*
> - * When no restart IP must always kill or panic.
> + * When no restart IP might need to kill or panic.
> + * Assume the worst for now, but if we find the
> + * severity is MCE_AR_SEVERITY we have other options.
> */
> if (!(m.mcgstatus & MCG_STATUS_RIPV))
> kill_it = 1;
> @@ -1036,12 +1038,6 @@ void do_machine_check(struct pt_regs *regs, long error_code)
> continue;
> }
>
> - /*
> - * Kill on action required.
> - */
> - if (severity == MCE_AR_SEVERITY)
> - kill_it = 1;
> -
> mce_read_aux(&m, i);
>
> /*
> @@ -1062,6 +1058,8 @@ void do_machine_check(struct pt_regs *regs, long error_code)
> }
> }
>
> + m = *final;
> +
> if (!no_way_out)
> mce_clear_state(toclear);
>
> @@ -1080,7 +1078,7 @@ void do_machine_check(struct pt_regs *regs, long error_code)
> * support MCE broadcasting or it has been disabled.
> */
> if (no_way_out && tolerant < 3)
> - mce_panic("Fatal machine check on current CPU", final, msg);
> + mce_panic("Fatal machine check on current CPU", &m, msg);
>
> /*
> * If the error seems to be unrecoverable, something should be
> @@ -1089,11 +1087,13 @@ void do_machine_check(struct pt_regs *regs, long error_code)
> * high, don't try to do anything at all.
> */
>
> - if (kill_it && tolerant < 3)
> + if (worst != MCE_AR_SEVERITY && kill_it && tolerant < 3)
> force_sig(SIGBUS, current);
>
> - /* notify userspace ASAP */
> - set_thread_flag(TIF_MCE_NOTIFY);
> + if (worst == MCE_AR_SEVERITY) {
> + mce_save_info(m.addr);
> + set_thread_flag(TIF_MCE_NOTIFY);
> + }
>
> if (worst > 0)
> mce_report_event(regs);
> @@ -1107,6 +1107,8 @@ EXPORT_SYMBOL_GPL(do_machine_check);
> #ifndef CONFIG_MEMORY_FAILURE
> int memory_failure(unsigned long pfn, int vector, int flags)
> {
> + if (flags & MF_ACTION_REQUIRED)
> + return -ENXIO; /* panic? */

Yes, an AR error _is_ an uncorrectable error so in order to stay
backwards-compatible, we should panic here unconditionally IMO.

> printk(KERN_ERR "Uncorrected memory error in page 0x%lx ignored\n"
> "Rebuild kernel with CONFIG_MEMORY_FAILURE=y for smarter handling\n", pfn);
>
> @@ -1115,27 +1117,46 @@ int memory_failure(unsigned long pfn, int vector, int flags)
> #endif
>
> /*
> - * 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 errorneous userland.

TIF_MCE_NOTIFY


> + * 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.
> + * Action required errors are handled here.
> */
> void mce_notify_process(void)
> {
> unsigned long pfn;
> - mce_notify_irq();
> - while (mce_ring_get(&pfn))
> - memory_failure(pfn, MCE_VECTOR, 0);
> + struct mce_info *mi = mce_find_info();
> +
> + if (!mi)
> + mce_panic("Lost address", NULL, NULL);

Yeah, maybe "Lost physical address for unconsumed uncorrectable error"

> + pfn = mi->paddr >> PAGE_SHIFT;
> +
> + clear_thread_flag(TIF_MCE_NOTIFY);
> +
> + pr_err("Uncorrected hardware memory error in user-access at %llx",
> + mi->paddr);
> + if (memory_failure(pfn, MCE_VECTOR, MF_ACTION_REQUIRED) < 0) {
> + pr_err("Memory error not recovered");
> + force_sig(SIGBUS, current);
> + } else {
> + pr_err("Memory error recovered");

No need for that because memory_failure() is chatty enough already, due
to action_result()?

> + }
> + mce_clear_info(mi);
> }
>
> +/*
> + * Action optional processing happens here (picking up
> + * from the list of faulting pages that do_machine_check()
> + * placed into the "ring").
> + */
> static void mce_process_work(struct work_struct *dummy)
> {
> - mce_notify_process();
> + unsigned long pfn;
> +
> + while (mce_ring_get(&pfn))
> + memory_failure(pfn, MCE_VECTOR, 0);
> }
>
> #ifdef CONFIG_X86_MCE_INTEL
> @@ -1225,8 +1246,6 @@ 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);
> --

Thanks.

--
Regards/Gruss,
Boris.

Advanced Micro Devices GmbH
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GM: Alberto Bozzo
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