On Tue, Sep 22, 2020 at 01:29:40PM -0500, miny...@acm.org wrote:
> From: Corey Minyard <cminy...@mvista.com>
>
> If kdump is enabled, the handling of shooting down CPUs does not use the
> RESET_VECTOR irq before trying to use NMIs to shoot down the CPUs.
>
> For normal errors that is fine. MCEs, however, are already running in
> an NMI, so sending them an NMI won't do anything. The MCE code is set
> up to receive the RESET_VECTOR because it disables CPUs, but it won't
^ should be "enables irqs"
> work on the NMI-only case.
>
> There is already code in place to scan for the NMI callback being ready,
> simply call that from the MCE's wait_for_panic() code so it will pick up
> and handle it if an NMI shootdown is requested. This required
> propagating the registers down to wait_for_panic().
>
> Signed-off-by: Corey Minyard <cminy...@mvista.com>
> ---
> After looking at it a bit, I think this is the proper way to fix the
> issue, though I'm not an expert on this code so I'm not sure.
>
> I have not even tested this patch, I have only compiled it. But from
> what I can tell, things waiting in NMIs for a shootdown should call
> run_crash_ipi_callback() in their wait loop.
>
> arch/x86/kernel/cpu/mce/core.c | 67 ++++++++++++++++++++++------------
> 1 file changed, 44 insertions(+), 23 deletions(-)
>
> diff --git a/arch/x86/kernel/cpu/mce/core.c b/arch/x86/kernel/cpu/mce/core.c
> index f43a78bde670..3a842b3773b3 100644
> --- a/arch/x86/kernel/cpu/mce/core.c
> +++ b/arch/x86/kernel/cpu/mce/core.c
> @@ -282,20 +282,35 @@ static int fake_panic;
> static atomic_t mce_fake_panicked;
>
> /* Panic in progress. Enable interrupts and wait for final IPI */
> -static void wait_for_panic(void)
> +static void wait_for_panic(struct pt_regs *regs)
> {
> long timeout = PANIC_TIMEOUT*USEC_PER_SEC;
>
> preempt_disable();
> local_irq_enable();
> - while (timeout-- > 0)
> + while (timeout-- > 0) {
> + /*
> + * We are in an NMI waiting to be stopped by the
> + * handing processor. For kdump handling, we need to
> + * be monitoring crash_ipi_issued since that is what
> + * is used for an NMI stop used by kdump. But we also
> + * need to have interrupts enabled some so that
> + * RESET_VECTOR will interrupt us on a normal
> + * shutdown.
> + */
> + local_irq_disable();
> + run_crash_ipi_callback(regs);
> + local_irq_enable();
> +
> udelay(1);
> + }
> if (panic_timeout == 0)
> panic_timeout = mca_cfg.panic_timeout;
> panic("Panicing machine check CPU died");
> }
>
> -static void mce_panic(const char *msg, struct mce *final, char *exp)
> +static void mce_panic(const char *msg, struct mce *final, char *exp,
> + struct pt_regs *regs)
> {
> int apei_err = 0;
> struct llist_node *pending;
> @@ -306,7 +321,7 @@ static void mce_panic(const char *msg, struct mce *final,
> char *exp)
> * Make sure only one CPU runs in machine check panic
> */
> if (atomic_inc_return(&mce_panicked) > 1)
> - wait_for_panic();
> + wait_for_panic(regs);
> barrier();
>
> bust_spinlocks(1);
> @@ -817,7 +832,7 @@ static atomic_t mce_callin;
> /*
> * Check if a timeout waiting for other CPUs happened.
> */
> -static int mce_timed_out(u64 *t, const char *msg)
> +static int mce_timed_out(u64 *t, const char *msg, struct pt_regs *regs)
> {
> /*
> * The others already did panic for some reason.
> @@ -827,12 +842,12 @@ static int mce_timed_out(u64 *t, const char *msg)
> */
> rmb();
> if (atomic_read(&mce_panicked))
> - wait_for_panic();
> + wait_for_panic(regs);
> if (!mca_cfg.monarch_timeout)
> goto out;
> if ((s64)*t < SPINUNIT) {
> if (mca_cfg.tolerant <= 1)
> - mce_panic(msg, NULL, NULL);
> + mce_panic(msg, NULL, NULL, regs);
> cpu_missing = 1;
> return 1;
> }
> @@ -866,7 +881,7 @@ static int mce_timed_out(u64 *t, const char *msg)
> * All the spin loops have timeouts; when a timeout happens a CPU
> * typically elects itself to be Monarch.
> */
> -static void mce_reign(void)
> +static void mce_reign(struct pt_regs *regs)
> {
> int cpu;
> struct mce *m = NULL;
> @@ -896,7 +911,7 @@ static void mce_reign(void)
> * other CPUs.
> */
> if (m && global_worst >= MCE_PANIC_SEVERITY && mca_cfg.tolerant < 3)
> - mce_panic("Fatal machine check", m, msg);
> + mce_panic("Fatal machine check", m, msg, regs);
>
> /*
> * For UC somewhere we let the CPU who detects it handle it.
> @@ -909,7 +924,8 @@ static void mce_reign(void)
> * source or one CPU is hung. Panic.
> */
> if (global_worst <= MCE_KEEP_SEVERITY && mca_cfg.tolerant < 3)
> - mce_panic("Fatal machine check from unknown source", NULL,
> NULL);
> + mce_panic("Fatal machine check from unknown source", NULL, NULL,
> + regs);
>
> /*
> * Now clear all the mces_seen so that they don't reappear on
> @@ -928,7 +944,7 @@ static atomic_t global_nwo;
> * in the entry order.
> * TBD double check parallel CPU hotunplug
> */
> -static int mce_start(int *no_way_out)
> +static int mce_start(int *no_way_out, struct pt_regs *regs)
> {
> int order;
> int cpus = num_online_cpus();
> @@ -949,7 +965,8 @@ static int mce_start(int *no_way_out)
> */
> while (atomic_read(&mce_callin) != cpus) {
> if (mce_timed_out(&timeout,
> - "Timeout: Not all CPUs entered broadcast
> exception handler")) {
> + "Timeout: Not all CPUs entered broadcast
> exception handler",
> + regs)) {
> atomic_set(&global_nwo, 0);
> return -1;
> }
> @@ -975,7 +992,8 @@ static int mce_start(int *no_way_out)
> */
> while (atomic_read(&mce_executing) < order) {
> if (mce_timed_out(&timeout,
> - "Timeout: Subject CPUs unable to
> finish machine check processing")) {
> + "Timeout: Subject CPUs unable to
> finish machine check processing",
> + regs)) {
> atomic_set(&global_nwo, 0);
> return -1;
> }
> @@ -995,7 +1013,7 @@ static int mce_start(int *no_way_out)
> * Synchronize between CPUs after main scanning loop.
> * This invokes the bulk of the Monarch processing.
> */
> -static int mce_end(int order)
> +static int mce_end(int order, struct pt_regs *regs)
> {
> int ret = -1;
> u64 timeout = (u64)mca_cfg.monarch_timeout * NSEC_PER_USEC;
> @@ -1020,12 +1038,13 @@ static int mce_end(int order)
> */
> while (atomic_read(&mce_executing) <= cpus) {
> if (mce_timed_out(&timeout,
> - "Timeout: Monarch CPU unable to
> finish machine check processing"))
> + "Timeout: Monarch CPU unable to
> finish machine check processing",
> + regs))
> goto reset;
> ndelay(SPINUNIT);
> }
>
> - mce_reign();
> + mce_reign(regs);
> barrier();
> ret = 0;
> } else {
> @@ -1034,7 +1053,8 @@ static int mce_end(int order)
> */
> while (atomic_read(&mce_executing) != 0) {
> if (mce_timed_out(&timeout,
> - "Timeout: Monarch CPU did not finish
> machine check processing"))
> + "Timeout: Monarch CPU did not finish
> machine check processing",
> + regs))
> goto reset;
> ndelay(SPINUNIT);
> }
> @@ -1286,9 +1306,9 @@ noinstr void do_machine_check(struct pt_regs *regs)
> */
> if (lmce) {
> if (no_way_out)
> - mce_panic("Fatal local machine check", &m, msg);
> + mce_panic("Fatal local machine check", &m, msg, regs);
> } else {
> - order = mce_start(&no_way_out);
> + order = mce_start(&no_way_out, regs);
> }
>
> __mc_scan_banks(&m, final, toclear, valid_banks, no_way_out, &worst);
> @@ -1301,7 +1321,7 @@ noinstr void do_machine_check(struct pt_regs *regs)
> * When there's any problem use only local no_way_out state.
> */
> if (!lmce) {
> - if (mce_end(order) < 0)
> + if (mce_end(order, regs) < 0)
> no_way_out = worst >= MCE_PANIC_SEVERITY;
> } else {
> /*
> @@ -1314,7 +1334,7 @@ noinstr void do_machine_check(struct pt_regs *regs)
> */
> if (worst >= MCE_PANIC_SEVERITY && mca_cfg.tolerant < 3) {
> mce_severity(&m, cfg->tolerant, &msg, true);
> - mce_panic("Local fatal machine check!", &m, msg);
> + mce_panic("Local fatal machine check!", &m, msg, regs);
> }
> }
>
> @@ -1325,7 +1345,7 @@ noinstr void do_machine_check(struct pt_regs *regs)
> if (cfg->tolerant == 3)
> kill_it = 0;
> else if (no_way_out)
> - mce_panic("Fatal machine check on current CPU", &m, msg);
> + mce_panic("Fatal machine check on current CPU", &m, msg, regs);
>
> if (worst > 0)
> irq_work_queue(&mce_irq_work);
> @@ -1361,7 +1381,8 @@ noinstr void do_machine_check(struct pt_regs *regs)
> */
> if (m.kflags & MCE_IN_KERNEL_RECOV) {
> if (!fixup_exception(regs, X86_TRAP_MC, 0, 0))
> - mce_panic("Failed kernel mode recovery", &m,
> msg);
> + mce_panic("Failed kernel mode recovery", &m,
> + msg, regs);
> }
> }
> }
> --
> 2.17.1
>
>
>
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