diff mbox series

[PULL,21/40] migration: per-mode blockers

Message ID 20231102114054.44360-22-quintela@redhat.com
State New
Headers show
Series [PULL,01/40] hw/ipmi: Don't call vmstate_register() from instance_init() functions | expand

Commit Message

Juan Quintela Nov. 2, 2023, 11:40 a.m. UTC
From: Steve Sistare <steven.sistare@oracle.com>

Extend the blocker interface so that a blocker can be registered for
one or more migration modes.  The existing interfaces register a
blocker for all modes, and the new interfaces take a varargs list
of modes.

Internally, maintain a separate blocker list per mode.  The same Error
object may be added to multiple lists.  When a block is deleted, it is
removed from every list, and the Error is freed.

No functional change until a new mode is added.

Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>
Message-ID: <1698263069-406971-3-git-send-email-steven.sistare@oracle.com>
---
 include/migration/blocker.h | 44 +++++++++++++++--
 migration/migration.c       | 95 ++++++++++++++++++++++++++++++++-----
 stubs/migr-blocker.c        | 10 ++++
 3 files changed, 132 insertions(+), 17 deletions(-)

Comments

Peter Maydell Nov. 9, 2023, 5:10 p.m. UTC | #1
On Thu, 2 Nov 2023 at 11:43, Juan Quintela <quintela@redhat.com> wrote:
>
> From: Steve Sistare <steven.sistare@oracle.com>
>
> Extend the blocker interface so that a blocker can be registered for
> one or more migration modes.  The existing interfaces register a
> blocker for all modes, and the new interfaces take a varargs list
> of modes.
>
> Internally, maintain a separate blocker list per mode.  The same Error
> object may be added to multiple lists.  When a block is deleted, it is
> removed from every list, and the Error is freed.
>
> No functional change until a new mode is added.

Hi; Coverity worries about this code:

> -static GSList *migration_blockers;
> +static GSList *migration_blockers[MIG_MODE__MAX];
>
>  static bool migration_object_check(MigrationState *ms, Error **errp);
>  static int migration_maybe_pause(MigrationState *s,
> @@ -1043,7 +1043,7 @@ static void fill_source_migration_info(MigrationInfo *info)
>  {
>      MigrationState *s = migrate_get_current();
>      int state = qatomic_read(&s->state);
> -    GSList *cur_blocker = migration_blockers;
> +    GSList *cur_blocker = migration_blockers[migrate_mode()];

because it thinks that migrate_mode() might return a value that's
too big for the migration_blockers[] array. (CID 1523829, 1523830.)

I think Coverity complains mostly because it doesn't understand
that the MIG_MODE__MAX in the enum is not a valid enum value
that a function returning a MigMode might return. But we can
help it out by assert()ing in migrate_mode() that the value
we're about to return is definitely a valid mode.

thanks
-- PMM
Steve Sistare Nov. 9, 2023, 5:24 p.m. UTC | #2
On 11/9/2023 12:10 PM, Peter Maydell wrote:
> On Thu, 2 Nov 2023 at 11:43, Juan Quintela <quintela@redhat.com> wrote:
>>
>> From: Steve Sistare <steven.sistare@oracle.com>
>>
>> Extend the blocker interface so that a blocker can be registered for
>> one or more migration modes.  The existing interfaces register a
>> blocker for all modes, and the new interfaces take a varargs list
>> of modes.
>>
>> Internally, maintain a separate blocker list per mode.  The same Error
>> object may be added to multiple lists.  When a block is deleted, it is
>> removed from every list, and the Error is freed.
>>
>> No functional change until a new mode is added.
> 
> Hi; Coverity worries about this code:
> 
>> -static GSList *migration_blockers;
>> +static GSList *migration_blockers[MIG_MODE__MAX];
>>
>>  static bool migration_object_check(MigrationState *ms, Error **errp);
>>  static int migration_maybe_pause(MigrationState *s,
>> @@ -1043,7 +1043,7 @@ static void fill_source_migration_info(MigrationInfo *info)
>>  {
>>      MigrationState *s = migrate_get_current();
>>      int state = qatomic_read(&s->state);
>> -    GSList *cur_blocker = migration_blockers;
>> +    GSList *cur_blocker = migration_blockers[migrate_mode()];
> 
> because it thinks that migrate_mode() might return a value that's
> too big for the migration_blockers[] array. (CID 1523829, 1523830.)
> 
> I think Coverity complains mostly because it doesn't understand
> that the MIG_MODE__MAX in the enum is not a valid enum value
> that a function returning a MigMode might return. But we can
> help it out by assert()ing in migrate_mode() that the value
> we're about to return is definitely a valid mode.

Thanks Peter, I will submit a fix with suggested-by, unless you want to.
I'll look at all uses of migration_blocker[].
Would coverity be happier if I also increase the size of the array?

- Steve
Peter Maydell Nov. 9, 2023, 5:27 p.m. UTC | #3
On Thu, 9 Nov 2023 at 17:24, Steven Sistare <steven.sistare@oracle.com> wrote:
>
> On 11/9/2023 12:10 PM, Peter Maydell wrote:
> > On Thu, 2 Nov 2023 at 11:43, Juan Quintela <quintela@redhat.com> wrote:
> >>
> >> From: Steve Sistare <steven.sistare@oracle.com>
> >>
> >> Extend the blocker interface so that a blocker can be registered for
> >> one or more migration modes.  The existing interfaces register a
> >> blocker for all modes, and the new interfaces take a varargs list
> >> of modes.
> >>
> >> Internally, maintain a separate blocker list per mode.  The same Error
> >> object may be added to multiple lists.  When a block is deleted, it is
> >> removed from every list, and the Error is freed.
> >>
> >> No functional change until a new mode is added.
> >
> > Hi; Coverity worries about this code:
> >
> >> -static GSList *migration_blockers;
> >> +static GSList *migration_blockers[MIG_MODE__MAX];
> >>
> >>  static bool migration_object_check(MigrationState *ms, Error **errp);
> >>  static int migration_maybe_pause(MigrationState *s,
> >> @@ -1043,7 +1043,7 @@ static void fill_source_migration_info(MigrationInfo *info)
> >>  {
> >>      MigrationState *s = migrate_get_current();
> >>      int state = qatomic_read(&s->state);
> >> -    GSList *cur_blocker = migration_blockers;
> >> +    GSList *cur_blocker = migration_blockers[migrate_mode()];
> >
> > because it thinks that migrate_mode() might return a value that's
> > too big for the migration_blockers[] array. (CID 1523829, 1523830.)
> >
> > I think Coverity complains mostly because it doesn't understand
> > that the MIG_MODE__MAX in the enum is not a valid enum value
> > that a function returning a MigMode might return. But we can
> > help it out by assert()ing in migrate_mode() that the value
> > we're about to return is definitely a valid mode.
>
> Thanks Peter, I will submit a fix with suggested-by, unless you want to.
> I'll look at all uses of migration_blocker[].
> Would coverity be happier if I also increase the size of the array?

Increasing the array size would also placate Coverity, but I think
in terms of actual bug possibilities the assert() is probably better,
as it would also catch the case of a garbage out-of-range value
getting written into the struct somehow.

thanks
-- PMM
diff mbox series

Patch

diff --git a/include/migration/blocker.h b/include/migration/blocker.h
index b048f301b4..a687ac0efe 100644
--- a/include/migration/blocker.h
+++ b/include/migration/blocker.h
@@ -14,8 +14,12 @@ 
 #ifndef MIGRATION_BLOCKER_H
 #define MIGRATION_BLOCKER_H
 
+#include "qapi/qapi-types-migration.h"
+
+#define MIG_MODE_ALL MIG_MODE__MAX
+
 /**
- * @migrate_add_blocker - prevent migration from proceeding
+ * @migrate_add_blocker - prevent all modes of migration from proceeding
  *
  * @reasonp - address of an error to be returned whenever migration is attempted
  *
@@ -30,8 +34,8 @@ 
 int migrate_add_blocker(Error **reasonp, Error **errp);
 
 /**
- * @migrate_add_blocker_internal - prevent migration from proceeding without
- *                                 only-migrate implications
+ * @migrate_add_blocker_internal - prevent all modes of migration from
+ *                                 proceeding, but ignore -only-migratable
  *
  * @reasonp - address of an error to be returned whenever migration is attempted
  *
@@ -50,7 +54,7 @@  int migrate_add_blocker(Error **reasonp, Error **errp);
 int migrate_add_blocker_internal(Error **reasonp, Error **errp);
 
 /**
- * @migrate_del_blocker - remove a blocking error from migration and free it.
+ * @migrate_del_blocker - remove a migration blocker from all modes and free it.
  *
  * @reasonp - address of the error blocking migration
  *
@@ -58,4 +62,36 @@  int migrate_add_blocker_internal(Error **reasonp, Error **errp);
  */
 void migrate_del_blocker(Error **reasonp);
 
+/**
+ * @migrate_add_blocker_normal - prevent normal migration mode from proceeding
+ *
+ * @reasonp - address of an error to be returned whenever migration is attempted
+ *
+ * @errp - [out] The reason (if any) we cannot block migration right now.
+ *
+ * @returns - 0 on success, -EBUSY/-EACCES on failure, with errp set.
+ *
+ * *@reasonp is freed and set to NULL if failure is returned.
+ * On success, the caller must not free @reasonp, except by
+ *   calling migrate_del_blocker.
+ */
+int migrate_add_blocker_normal(Error **reasonp, Error **errp);
+
+/**
+ * @migrate_add_blocker_modes - prevent some modes of migration from proceeding
+ *
+ * @reasonp - address of an error to be returned whenever migration is attempted
+ *
+ * @errp - [out] The reason (if any) we cannot block migration right now.
+ *
+ * @mode - one or more migration modes to be blocked.  The list is terminated
+ *         by -1 or MIG_MODE_ALL.  For the latter, all modes are blocked.
+ *
+ * @returns - 0 on success, -EBUSY/-EACCES on failure, with errp set.
+ *
+ * *@reasonp is freed and set to NULL if failure is returned.
+ * On success, the caller must not free *@reasonp before the blocker is removed.
+ */
+int migrate_add_blocker_modes(Error **reasonp, Error **errp, MigMode mode, ...);
+
 #endif
diff --git a/migration/migration.c b/migration/migration.c
index c334b9effd..11c1490090 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -92,7 +92,7 @@  enum mig_rp_message_type {
 static MigrationState *current_migration;
 static MigrationIncomingState *current_incoming;
 
-static GSList *migration_blockers;
+static GSList *migration_blockers[MIG_MODE__MAX];
 
 static bool migration_object_check(MigrationState *ms, Error **errp);
 static int migration_maybe_pause(MigrationState *s,
@@ -1043,7 +1043,7 @@  static void fill_source_migration_info(MigrationInfo *info)
 {
     MigrationState *s = migrate_get_current();
     int state = qatomic_read(&s->state);
-    GSList *cur_blocker = migration_blockers;
+    GSList *cur_blocker = migration_blockers[migrate_mode()];
 
     info->blocked_reasons = NULL;
 
@@ -1507,38 +1507,105 @@  int migrate_init(MigrationState *s, Error **errp)
     return 0;
 }
 
-int migrate_add_blocker_internal(Error **reasonp, Error **errp)
+static bool is_busy(Error **reasonp, Error **errp)
 {
+    ERRP_GUARD();
+
     /* Snapshots are similar to migrations, so check RUN_STATE_SAVE_VM too. */
     if (runstate_check(RUN_STATE_SAVE_VM) || !migration_is_idle()) {
         error_propagate_prepend(errp, *reasonp,
                                 "disallowing migration blocker "
                                 "(migration/snapshot in progress) for: ");
         *reasonp = NULL;
-        return -EBUSY;
+        return true;
     }
-
-    migration_blockers = g_slist_prepend(migration_blockers, *reasonp);
-    return 0;
+    return false;
 }
 
-int migrate_add_blocker(Error **reasonp, Error **errp)
+static bool is_only_migratable(Error **reasonp, Error **errp, int modes)
 {
-    if (only_migratable) {
+    ERRP_GUARD();
+
+    if (only_migratable && (modes & BIT(MIG_MODE_NORMAL))) {
         error_propagate_prepend(errp, *reasonp,
                                 "disallowing migration blocker "
                                 "(--only-migratable) for: ");
         *reasonp = NULL;
+        return true;
+    }
+    return false;
+}
+
+static int get_modes(MigMode mode, va_list ap)
+{
+    int modes = 0;
+
+    while (mode != -1 && mode != MIG_MODE_ALL) {
+        assert(mode >= MIG_MODE_NORMAL && mode < MIG_MODE__MAX);
+        modes |= BIT(mode);
+        mode = va_arg(ap, MigMode);
+    }
+    if (mode == MIG_MODE_ALL) {
+        modes = BIT(MIG_MODE__MAX) - 1;
+    }
+    return modes;
+}
+
+static int add_blockers(Error **reasonp, Error **errp, int modes)
+{
+    for (MigMode mode = 0; mode < MIG_MODE__MAX; mode++) {
+        if (modes & BIT(mode)) {
+            migration_blockers[mode] = g_slist_prepend(migration_blockers[mode],
+                                                       *reasonp);
+        }
+    }
+    return 0;
+}
+
+int migrate_add_blocker(Error **reasonp, Error **errp)
+{
+    return migrate_add_blocker_modes(reasonp, errp, MIG_MODE_ALL);
+}
+
+int migrate_add_blocker_normal(Error **reasonp, Error **errp)
+{
+    return migrate_add_blocker_modes(reasonp, errp, MIG_MODE_NORMAL, -1);
+}
+
+int migrate_add_blocker_modes(Error **reasonp, Error **errp, MigMode mode, ...)
+{
+    int modes;
+    va_list ap;
+
+    va_start(ap, mode);
+    modes = get_modes(mode, ap);
+    va_end(ap);
+
+    if (is_only_migratable(reasonp, errp, modes)) {
         return -EACCES;
+    } else if (is_busy(reasonp, errp)) {
+        return -EBUSY;
     }
+    return add_blockers(reasonp, errp, modes);
+}
 
-    return migrate_add_blocker_internal(reasonp, errp);
+int migrate_add_blocker_internal(Error **reasonp, Error **errp)
+{
+    int modes = BIT(MIG_MODE__MAX) - 1;
+
+    if (is_busy(reasonp, errp)) {
+        return -EBUSY;
+    }
+    return add_blockers(reasonp, errp, modes);
 }
 
 void migrate_del_blocker(Error **reasonp)
 {
     if (*reasonp) {
-        migration_blockers = g_slist_remove(migration_blockers, *reasonp);
+        for (MigMode mode = 0; mode < MIG_MODE__MAX; mode++) {
+            migration_blockers[mode] = g_slist_remove(migration_blockers[mode],
+                                                      *reasonp);
+        }
         error_free(*reasonp);
         *reasonp = NULL;
     }
@@ -1634,12 +1701,14 @@  void qmp_migrate_pause(Error **errp)
 
 bool migration_is_blocked(Error **errp)
 {
+    GSList *blockers = migration_blockers[migrate_mode()];
+
     if (qemu_savevm_state_blocked(errp)) {
         return true;
     }
 
-    if (migration_blockers) {
-        error_propagate(errp, error_copy(migration_blockers->data));
+    if (blockers) {
+        error_propagate(errp, error_copy(blockers->data));
         return true;
     }
 
diff --git a/stubs/migr-blocker.c b/stubs/migr-blocker.c
index 17a5dbf87b..11cbff268f 100644
--- a/stubs/migr-blocker.c
+++ b/stubs/migr-blocker.c
@@ -6,6 +6,16 @@  int migrate_add_blocker(Error **reasonp, Error **errp)
     return 0;
 }
 
+int migrate_add_blocker_normal(Error **reasonp, Error **errp)
+{
+    return 0;
+}
+
+int migrate_add_blocker_modes(Error **reasonp, Error **errp, MigMode mode, ...)
+{
+    return 0;
+}
+
 void migrate_del_blocker(Error **reasonp)
 {
 }