[Xen-changelog] [xen staging] cpu: sync any remaining RCU callbacks before CPU up/down

[patchbot@xxxxxxx]

commit 540d4d60378ca8ded405c19a38d4dcce61e3462e
Author:     Igor Druzhinin <igor.druzhinin@xxxxxxxxxx>
AuthorDate: Thu Mar 26 12:49:42 2020 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Thu Mar 26 12:49:42 2020 +0100

    cpu: sync any remaining RCU callbacks before CPU up/down
    
    During CPU down operation RCU callbacks are scheduled to finish
    off some actions later as soon as CPU is fully dead (the same applies
    to CPU up operation in case error path is taken). If in the same grace
    period another CPU up operation is performed on the same CPU, RCU callback
    will be called later on a CPU in a potentially wrong (already up again
    instead of still being down) state leading to eventual state inconsistency
    and/or crash.
    
    In order to avoid it - flush RCU callbacks explicitly before starting the
    next CPU up/down operation.
    
    Signed-off-by: Igor Druzhinin <igor.druzhinin@xxxxxxxxxx>
    Reviewed-by: Juergen Gross <jgross@xxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 xen/arch/x86/acpi/power.c |  1 -
 xen/arch/x86/sysctl.c     | 10 ++--------
 xen/common/cpu.c          |  2 ++
 3 files changed, 4 insertions(+), 9 deletions(-)

diff --git a/xen/arch/x86/acpi/power.c b/xen/arch/x86/acpi/power.c
index e3d6eefe65..3ad7dfc9a3 100644
--- a/xen/arch/x86/acpi/power.c
+++ b/xen/arch/x86/acpi/power.c
@@ -306,7 +306,6 @@ static int enter_state(u32 state)
     cpufreq_add_cpu(0);
 
  enable_cpu:
-    rcu_barrier();
     mtrr_aps_sync_begin();
     enable_nonboot_cpus();
     mtrr_aps_sync_end();
diff --git a/xen/arch/x86/sysctl.c b/xen/arch/x86/sysctl.c
index a95923e591..b0cb1b57e7 100644
--- a/xen/arch/x86/sysctl.c
+++ b/xen/arch/x86/sysctl.c
@@ -84,12 +84,9 @@ long cpu_up_helper(void *data)
     unsigned int cpu = (unsigned long)data;
     int ret = cpu_up(cpu);
 
+    /* Have one more go on EBUSY. */
     if ( ret == -EBUSY )
-    {
-        /* On EBUSY, flush RCU work and have one more go. */
-        rcu_barrier();
         ret = cpu_up(cpu);
-    }
 
     if ( !ret && !opt_smt &&
          cpu_data[cpu].compute_unit_id == INVALID_CUID &&
@@ -109,12 +106,9 @@ long cpu_down_helper(void *data)
 {
     int cpu = (unsigned long)data;
     int ret = cpu_down(cpu);
+    /* Have one more go on EBUSY. */
     if ( ret == -EBUSY )
-    {
-        /* On EBUSY, flush RCU work and have one more go. */
-        rcu_barrier();
         ret = cpu_down(cpu);
-    }
     return ret;
 }
 
diff --git a/xen/common/cpu.c b/xen/common/cpu.c
index 31953f32e4..1f976db0a5 100644
--- a/xen/common/cpu.c
+++ b/xen/common/cpu.c
@@ -4,6 +4,7 @@
 #include <xen/init.h>
 #include <xen/sched.h>
 #include <xen/stop_machine.h>
+#include <xen/rcupdate.h>
 
 unsigned int __read_mostly nr_cpu_ids = NR_CPUS;
 #ifndef nr_cpumask_bits
@@ -53,6 +54,7 @@ void put_cpu_maps(void)
 
 void cpu_hotplug_begin(void)
 {
+    rcu_barrier();
     write_lock(&cpu_add_remove_lock);
 }
 
--
generated by git-patchbot for /home/xen/git/xen.git#staging

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