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authorDavid Hildenbrand <david@redhat.com>2021-04-13 11:55:28 +0200
committerEduardo Habkost <ehabkost@redhat.com>2021-07-08 15:54:45 -0400
commit98da491dff558df95768c5f81243fc49c6360a91 (patch)
tree4b527897cc537201029fe3d11ae7e8d4d4e92767 /softmmu/physmem.c
parent0fd7616e0f1171b8149bb71f59e23ab048a8df83 (diff)
softmmu/physmem: Don't use atomic operations in ram_block_discard_(disable|require)
We have users in migration context that don't hold the BQL (when finishing migration). To prepare for further changes, use a dedicated mutex instead of atomic operations. Keep using qatomic_read ("READ_ONCE") for the functions that only extract the current state (e.g., used by virtio-balloon), locking isn't necessary. While at it, split up the counter into two variables to make it easier to understand. Suggested-by: Peter Xu <peterx@redhat.com> Reviewed-by: Peter Xu <peterx@redhat.com> Reviewed-by: Pankaj Gupta <pankaj.gupta@cloud.ionos.com> Acked-by: Michael S. Tsirkin <mst@redhat.com> Cc: Paolo Bonzini <pbonzini@redhat.com> Cc: "Michael S. Tsirkin" <mst@redhat.com> Cc: Alex Williamson <alex.williamson@redhat.com> Cc: Dr. David Alan Gilbert <dgilbert@redhat.com> Cc: Igor Mammedov <imammedo@redhat.com> Cc: Pankaj Gupta <pankaj.gupta.linux@gmail.com> Cc: Peter Xu <peterx@redhat.com> Cc: Auger Eric <eric.auger@redhat.com> Cc: Wei Yang <richard.weiyang@linux.alibaba.com> Cc: teawater <teawaterz@linux.alibaba.com> Cc: Marek Kedzierski <mkedzier@redhat.com> Signed-off-by: David Hildenbrand <david@redhat.com> Message-Id: <20210413095531.25603-11-david@redhat.com> Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Diffstat (limited to 'softmmu/physmem.c')
-rw-r--r--softmmu/physmem.c70
1 files changed, 39 insertions, 31 deletions
diff --git a/softmmu/physmem.c b/softmmu/physmem.c
index 9b171c9dbe..f1275b61f8 100644
--- a/softmmu/physmem.c
+++ b/softmmu/physmem.c
@@ -3684,56 +3684,64 @@ void mtree_print_dispatch(AddressSpaceDispatch *d, MemoryRegion *root)
}
}
-/*
- * If positive, discarding RAM is disabled. If negative, discarding RAM is
- * required to work and cannot be disabled.
- */
-static int ram_block_discard_disabled;
+static unsigned int ram_block_discard_required_cnt;
+static unsigned int ram_block_discard_disabled_cnt;
+static QemuMutex ram_block_discard_disable_mutex;
+
+static void ram_block_discard_disable_mutex_lock(void)
+{
+ static gsize initialized;
+
+ if (g_once_init_enter(&initialized)) {
+ qemu_mutex_init(&ram_block_discard_disable_mutex);
+ g_once_init_leave(&initialized, 1);
+ }
+ qemu_mutex_lock(&ram_block_discard_disable_mutex);
+}
+
+static void ram_block_discard_disable_mutex_unlock(void)
+{
+ qemu_mutex_unlock(&ram_block_discard_disable_mutex);
+}
int ram_block_discard_disable(bool state)
{
- int old;
+ int ret = 0;
+ ram_block_discard_disable_mutex_lock();
if (!state) {
- qatomic_dec(&ram_block_discard_disabled);
- return 0;
+ ram_block_discard_disabled_cnt--;
+ } else if (!ram_block_discard_required_cnt) {
+ ram_block_discard_disabled_cnt++;
+ } else {
+ ret = -EBUSY;
}
-
- do {
- old = qatomic_read(&ram_block_discard_disabled);
- if (old < 0) {
- return -EBUSY;
- }
- } while (qatomic_cmpxchg(&ram_block_discard_disabled,
- old, old + 1) != old);
- return 0;
+ ram_block_discard_disable_mutex_unlock();
+ return ret;
}
int ram_block_discard_require(bool state)
{
- int old;
+ int ret = 0;
+ ram_block_discard_disable_mutex_lock();
if (!state) {
- qatomic_inc(&ram_block_discard_disabled);
- return 0;
+ ram_block_discard_required_cnt--;
+ } else if (!ram_block_discard_disabled_cnt) {
+ ram_block_discard_required_cnt++;
+ } else {
+ ret = -EBUSY;
}
-
- do {
- old = qatomic_read(&ram_block_discard_disabled);
- if (old > 0) {
- return -EBUSY;
- }
- } while (qatomic_cmpxchg(&ram_block_discard_disabled,
- old, old - 1) != old);
- return 0;
+ ram_block_discard_disable_mutex_unlock();
+ return ret;
}
bool ram_block_discard_is_disabled(void)
{
- return qatomic_read(&ram_block_discard_disabled) > 0;
+ return qatomic_read(&ram_block_discard_disabled_cnt);
}
bool ram_block_discard_is_required(void)
{
- return qatomic_read(&ram_block_discard_disabled) < 0;
+ return qatomic_read(&ram_block_discard_required_cnt);
}