powerpc/kexec: Fix race in kexec shutdown

In kexec_prepare_cpus, the primary CPU IPIs the secondary CPUs to
kexec_smp_down().  kexec_smp_down() calls kexec_smp_wait() which sets
the hw_cpu_id() to -1.  The primary does this while leaving IRQs on
which means the primary can take a timer interrupt which can lead to
the IPIing one of the secondary CPUs (say, for a scheduler re-balance)
but since the secondary CPU now has a hw_cpu_id = -1, we IPI CPU
-1... Kaboom!

We are hitting this case regularly on POWER7 machines.

There is also a second race, where the primary will tear down the MMU
mappings before knowing the secondaries have entered real mode.

Also, the secondaries are clearing out any pending IPIs before
guaranteeing that no more will be received.

This changes kexec_prepare_cpus() so that we turn off IRQs in the
primary CPU much earlier.  It adds a paca flag to say that the
secondaries have entered the kexec_smp_down() IPI and turned off IRQs,
rather than overloading hw_cpu_id with -1.  This new paca flag is
again used to in indicate when the secondaries has entered real mode.

It also ensures that all CPUs have their IRQs off before we clear out
any pending IPI requests (in kexec_cpu_down()) to ensure there are no
trailing IPIs left unacknowledged.

Signed-off-by: Michael Neuling <mikey@neuling.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

diff --git a/arch/powerpc/include/asm/kexec.h b/arch/powerpc/include/asm/kexec.h
index 7e06b43720d3ce0ce439c50b4ba980f6e398fc01..a6ca6da1430bd60506af9b5babc62df147c8c9f7 100644 (file)
--- a/arch/powerpc/include/asm/kexec.h
+++ b/arch/powerpc/include/asm/kexec.h
@@ -31,6 +31,10 @@
 #define KEXEC_ARCH KEXEC_ARCH_PPC
 #endif
 
+#define KEXEC_STATE_NONE 0
+#define KEXEC_STATE_IRQS_OFF 1
+#define KEXEC_STATE_REAL_MODE 2
+
 #ifndef __ASSEMBLY__
 #include <linux/cpumask.h>
 #include <asm/reg.h>

diff --git a/arch/powerpc/include/asm/paca.h b/arch/powerpc/include/asm/paca.h
index a011603d407902c87555fbbff5a5c48afe5255a9..971dfa4815f02fa8e02ac604c0e1e869b7b05234 100644 (file)
--- a/arch/powerpc/include/asm/paca.h
+++ b/arch/powerpc/include/asm/paca.h
@@ -82,6 +82,7 @@ struct paca_struct {
        s16 hw_cpu_id;                  /* Physical processor number */
        u8 cpu_start;                   /* At startup, processor spins until */
                                        /* this becomes non-zero. */
+       u8 kexec_state;         /* set when kexec down has irqs off */
 #ifdef CONFIG_PPC_STD_MMU_64
        struct slb_shadow *slb_shadow_ptr;
 

diff --git a/arch/powerpc/kernel/asm-offsets.c b/arch/powerpc/kernel/asm-offsets.c
index 0271b58ec31e427ac3783a0a39e62622f93b4a4a..1b784ff92d9d06a5f162790fcaa6f1ddd1055b57 100644 (file)
--- a/arch/powerpc/kernel/asm-offsets.c
+++ b/arch/powerpc/kernel/asm-offsets.c
@@ -184,6 +184,7 @@ int main(void)
 #endif /* CONFIG_PPC_STD_MMU_64 */
        DEFINE(PACAEMERGSP, offsetof(struct paca_struct, emergency_sp));
        DEFINE(PACAHWCPUID, offsetof(struct paca_struct, hw_cpu_id));
+       DEFINE(PACAKEXECSTATE, offsetof(struct paca_struct, kexec_state));
        DEFINE(PACA_STARTPURR, offsetof(struct paca_struct, startpurr));
        DEFINE(PACA_STARTSPURR, offsetof(struct paca_struct, startspurr));
        DEFINE(PACA_USER_TIME, offsetof(struct paca_struct, user_time));

diff --git a/arch/powerpc/kernel/machine_kexec_64.c b/arch/powerpc/kernel/machine_kexec_64.c
index 040bd1de8d99b68b46d36008aca44420ffd180c3..26f9900f773cb2e17634538f1674882c0cd7447b 100644 (file)
--- a/arch/powerpc/kernel/machine_kexec_64.c
+++ b/arch/powerpc/kernel/machine_kexec_64.c
@@ -155,33 +155,38 @@ void kexec_copy_flush(struct kimage *image)
 
 #ifdef CONFIG_SMP
 
-/* FIXME: we should schedule this function to be called on all cpus based
- * on calling the interrupts, but we would like to call it off irq level
- * so that the interrupt controller is clean.
- */
+static int kexec_all_irq_disabled = 0;
+
 static void kexec_smp_down(void *arg)
 {
+       local_irq_disable();
+       mb(); /* make sure our irqs are disabled before we say they are */
+       get_paca()->kexec_state = KEXEC_STATE_IRQS_OFF;
+       while(kexec_all_irq_disabled == 0)
+               cpu_relax();
+       mb(); /* make sure all irqs are disabled before this */
+       /*
+        * Now every CPU has IRQs off, we can clear out any pending
+        * IPIs and be sure that no more will come in after this.
+        */
        if (ppc_md.kexec_cpu_down)
                ppc_md.kexec_cpu_down(0, 1);
 
-       local_irq_disable();
        kexec_smp_wait();
        /* NOTREACHED */
 }
 
-static void kexec_prepare_cpus(void)
+static void kexec_prepare_cpus_wait(int wait_state)
 {
        int my_cpu, i, notified=-1;
 
-       smp_call_function(kexec_smp_down, NULL, /* wait */0);
        my_cpu = get_cpu();
-
-       /* check the others cpus are now down (via paca hw cpu id == -1) */
+       /* Make sure each CPU has atleast made it to the state we need */
        for (i=0; i < NR_CPUS; i++) {
                if (i == my_cpu)
                        continue;
 
-               while (paca[i].hw_cpu_id != -1) {
+               while (paca[i].kexec_state < wait_state) {
                        barrier();
                        if (!cpu_possible(i)) {
                                printk("kexec: cpu %d hw_cpu_id %d is not"
@@ -201,20 +206,35 @@ static void kexec_prepare_cpus(void)
                        }
                        if (i != notified) {
                                printk( "kexec: waiting for cpu %d (physical"
-                                               " %d) to go down\n",
-                                               i, paca[i].hw_cpu_id);
+                                               " %d) to enter %i state\n",
+                                       i, paca[i].hw_cpu_id, wait_state);
                                notified = i;
                        }
                }
        }
+       mb();
+}
+
+static void kexec_prepare_cpus(void)
+{
+
+       smp_call_function(kexec_smp_down, NULL, /* wait */0);
+       local_irq_disable();
+       mb(); /* make sure IRQs are disabled before we say they are */
+       get_paca()->kexec_state = KEXEC_STATE_IRQS_OFF;
+
+       kexec_prepare_cpus_wait(KEXEC_STATE_IRQS_OFF);
+       /* we are sure every CPU has IRQs off at this point */
+       kexec_all_irq_disabled = 1;
 
        /* after we tell the others to go down */
        if (ppc_md.kexec_cpu_down)
                ppc_md.kexec_cpu_down(0, 0);
 
-       put_cpu();
+       /* Before removing MMU mapings make sure all CPUs have entered real mode */
+       kexec_prepare_cpus_wait(KEXEC_STATE_REAL_MODE);
 
-       local_irq_disable();
+       put_cpu();
 }
 
 #else /* ! SMP */

diff --git a/arch/powerpc/kernel/misc_64.S b/arch/powerpc/kernel/misc_64.S
index a5cf9c1356a674c05d902bcf71e1b0c8a4b4bef1..a2b18dffa03e4266a402aa58f8118e45fdffa74f 100644 (file)
--- a/arch/powerpc/kernel/misc_64.S
+++ b/arch/powerpc/kernel/misc_64.S
@@ -24,6 +24,7 @@
 #include <asm/asm-offsets.h>
 #include <asm/cputable.h>
 #include <asm/thread_info.h>
+#include <asm/kexec.h>
 
        .text
 
@@ -471,6 +472,10 @@ _GLOBAL(kexec_wait)
 1:     mflr    r5
        addi    r5,r5,kexec_flag-1b
 
+       li      r4,KEXEC_STATE_REAL_MODE
+       stb     r4,PACAKEXECSTATE(r13)
+       SYNC
+
 99:    HMT_LOW
 #ifdef CONFIG_KEXEC            /* use no memory without kexec */
        lwz     r4,0(r5)
@@ -494,14 +499,11 @@ kexec_flag:
  * note: this is a terminal routine, it does not save lr
  *
  * get phys id from paca
- * set paca id to -1 to say we got here
  * switch to real mode
  * join other cpus in kexec_wait(phys_id)
  */
 _GLOBAL(kexec_smp_wait)
        lhz     r3,PACAHWCPUID(r13)
-       li      r4,-1
-       sth     r4,PACAHWCPUID(r13)     /* let others know we left */
        bl      real_mode
        b       .kexec_wait
 

diff --git a/arch/powerpc/kernel/paca.c b/arch/powerpc/kernel/paca.c
index 0c40c6f476fe0fb26edd67c37352c86826dc6661..f88acf0218dbfdbe30dc0f65f20326ae5a38ee7d 100644 (file)
--- a/arch/powerpc/kernel/paca.c
+++ b/arch/powerpc/kernel/paca.c
@@ -18,6 +18,7 @@
 #include <asm/pgtable.h>
 #include <asm/iseries/lpar_map.h>
 #include <asm/iseries/hv_types.h>
+#include <asm/kexec.h>
 
 /* This symbol is provided by the linker - let it fill in the paca
  * field correctly */
@@ -97,6 +98,7 @@ void __init initialise_paca(struct paca_struct *new_paca, int cpu)
        new_paca->kernelbase = (unsigned long) _stext;
        new_paca->kernel_msr = MSR_KERNEL;
        new_paca->hw_cpu_id = 0xffff;
+       new_paca->kexec_state = KEXEC_STATE_NONE;
        new_paca->__current = &init_task;
 #ifdef CONFIG_PPC_STD_MMU_64
        new_paca->slb_shadow_ptr = &slb_shadow[cpu];