[Xen-changelog] [xen stable-4.12] xen/timers: Fix memory leak with cpu unplug/plug

[patchbot@xxxxxxx]

commit 0bd5e03cb75a3b1a2881f3162342064ceeae3c77
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Wed May 15 09:40:00 2019 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Wed May 15 09:40:00 2019 +0200

    xen/timers: Fix memory leak with cpu unplug/plug
    
    timer_softirq_action() realloc's itself a larger timer heap whenever
    necessary, which includes bootstrapping from the empty dummy_heap.  Nothing
    ever freed this allocation.
    
    CPU plug and unplug has the side effect of zeroing the percpu data area, 
which
    clears ts->heap.  This in turn causes new timers to be put on the list 
rather
    than the heap, and for timer_softirq_action() to bootstrap itself again.
    
    This in practice leaks ts->heap every time a CPU is unplugged and replugged.
    
    Implement free_percpu_timers() which includes freeing ts->heap when
    appropriate, and update the notifier callback with the recent cpu parking
    logic and free-avoidance across suspend.
    
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
    
    xen/cpu: Fix ARM build following c/s 597fbb8
    
    c/s 597fbb8 "xen/timers: Fix memory leak with cpu unplug/plug" broke the ARM
    build by being the first patch to add park_offline_cpus to common code.
    
    While it is currently specific to Intel hardware (for reasons of being able 
to
    handle machine check exceptions without an immediate system reset), it isn't
    inherently architecture specific, so define it to be false on ARM for now.
    
    Add a comment in both smp.h headers explaining the intended behaviour of the
    option.
    
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Reviewed-by: Julien Grall <julien.grall@xxxxxxx>
    Reviewed-by: Wei Liu <wei.liu2@xxxxxxxxxx>
    
    timers: move back migrate_timers_from_cpu() invocation
    
    Commit 597fbb8be6 ("xen/timers: Fix memory leak with cpu unplug/plug")
    went a little too far: Migrating timers away from a CPU being offlined
    needs to heppen independent of whether it get parked or fully offlined.
    
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    
    xen/timers: Fix memory leak with cpu unplug/plug (take 2)
    
    Previous attempts to fix this leak failed to identify the root cause, and
    ultimately failed.  The cause is the CPU_UP_PREPARE case (re)initialising
    ts->heap back to dummy_heap, which leaks the previous allocation.
    
    Rearrange the logic to only initialise ts once.  This also avoids the
    redundant (but benign, due to ts->inactive always being empty) initialising 
of
    the other ts fields.
    
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
    master commit: 597fbb8be6021440cd53493c14201c32671bade1
    master date: 2019-04-08 11:16:06 +0100
    master commit: a6448adfd3d537aacbbd784e5bf1777ab3ff5f85
    master date: 2019-04-09 10:12:57 +0100
    master commit: 1aec95350ac8261cba516371710d4d837c26f6a0
    master date: 2019-04-15 17:51:30 +0100
    master commit: e978e9ed9e1ff0dc326e72708ed03cac2ba41db8
    master date: 2019-05-13 10:35:37 +0100
---
 xen/common/timer.c        | 34 +++++++++++++++++++++++++++++++---
 xen/include/asm-arm/smp.h |  6 ++++++
 xen/include/asm-x86/smp.h |  4 ++++
 3 files changed, 41 insertions(+), 3 deletions(-)

diff --git a/xen/common/timer.c b/xen/common/timer.c
index 376581bd54..12fcd952fd 100644
--- a/xen/common/timer.c
+++ b/xen/common/timer.c
@@ -601,6 +601,20 @@ static void migrate_timers_from_cpu(unsigned int old_cpu)
 
 static struct timer *dummy_heap;
 
+static void free_percpu_timers(unsigned int cpu)
+{
+    struct timers *ts = &per_cpu(timers, cpu);
+
+    ASSERT(GET_HEAP_SIZE(ts->heap) == 0);
+    if ( GET_HEAP_LIMIT(ts->heap) )
+    {
+        xfree(ts->heap);
+        ts->heap = &dummy_heap;
+    }
+    else
+        ASSERT(ts->heap == &dummy_heap);
+}
+
 static int cpu_callback(
     struct notifier_block *nfb, unsigned long action, void *hcpu)
 {
@@ -610,14 +624,28 @@ static int cpu_callback(
     switch ( action )
     {
     case CPU_UP_PREPARE:
-        INIT_LIST_HEAD(&ts->inactive);
-        spin_lock_init(&ts->lock);
-        ts->heap = &dummy_heap;
+        /* Only initialise ts once. */
+        if ( !ts->heap )
+        {
+            INIT_LIST_HEAD(&ts->inactive);
+            spin_lock_init(&ts->lock);
+            ts->heap = &dummy_heap;
+        }
         break;
+
     case CPU_UP_CANCELED:
     case CPU_DEAD:
         migrate_timers_from_cpu(cpu);
+
+        if ( !park_offline_cpus && system_state != SYS_STATE_suspend )
+            free_percpu_timers(cpu);
+        break;
+
+    case CPU_REMOVE:
+        if ( park_offline_cpus )
+            free_percpu_timers(cpu);
         break;
+
     default:
         break;
     }
diff --git a/xen/include/asm-arm/smp.h b/xen/include/asm-arm/smp.h
index 3c122681d7..fdbcefa241 100644
--- a/xen/include/asm-arm/smp.h
+++ b/xen/include/asm-arm/smp.h
@@ -14,6 +14,12 @@ DECLARE_PER_CPU(cpumask_var_t, cpu_core_mask);
 
 #define raw_smp_processor_id() (get_processor_id())
 
+/*
+ * Do we, for platform reasons, need to actually keep CPUs online when we
+ * would otherwise prefer them to be off?
+ */
+#define park_offline_cpus false
+
 extern void noreturn stop_cpu(void);
 
 extern int arch_smp_init(void);
diff --git a/xen/include/asm-x86/smp.h b/xen/include/asm-x86/smp.h
index 09c55458df..9f533f9072 100644
--- a/xen/include/asm-x86/smp.h
+++ b/xen/include/asm-x86/smp.h
@@ -26,6 +26,10 @@ DECLARE_PER_CPU(cpumask_var_t, cpu_sibling_mask);
 DECLARE_PER_CPU(cpumask_var_t, cpu_core_mask);
 DECLARE_PER_CPU(cpumask_var_t, scratch_cpumask);
 
+/*
+ * Do we, for platform reasons, need to actually keep CPUs online when we
+ * would otherwise prefer them to be off?
+ */
 extern bool park_offline_cpus;
 
 void smp_send_nmi_allbutself(void);
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.12

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