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 <pet...@redhat.com>
Reviewed-by: Peter Xu <pet...@redhat.com>
Reviewed-by: Pankaj Gupta <pankaj.gu...@cloud.ionos.com>
Cc: Paolo Bonzini <pbonz...@redhat.com>
Cc: "Michael S. Tsirkin" <m...@redhat.com>
Cc: Alex Williamson <alex.william...@redhat.com>
Cc: Dr. David Alan Gilbert <dgilb...@redhat.com>
Cc: Igor Mammedov <imamm...@redhat.com>
Cc: Pankaj Gupta <pankaj.gupta.li...@gmail.com>
Cc: Peter Xu <pet...@redhat.com>
Cc: Auger Eric <eric.au...@redhat.com>
Cc: Wei Yang <richard.weiy...@linux.alibaba.com>
Cc: teawater <teawat...@linux.alibaba.com>
Cc: Marek Kedzierski <mkedz...@redhat.com>
Signed-off-by: David Hildenbrand <da...@redhat.com>
---
softmmu/physmem.c | 70 ++++++++++++++++++++++++++---------------------
1 file changed, 39 insertions(+), 31 deletions(-)
diff --git a/softmmu/physmem.c b/softmmu/physmem.c
index 6301f4f0a5..2e253b8547 100644
--- a/softmmu/physmem.c
+++ b/softmmu/physmem.c
@@ -3660,56 +3660,64 @@ 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_requirers;
+static unsigned int ram_block_discard_disablers;
+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_disablers--;
+ } else if (!ram_block_discard_requirers) {
+ ram_block_discard_disablers++;
+ } 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_requirers--;
+ } else if (!ram_block_discard_disablers) {
+ ram_block_discard_requirers++;
+ } 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_disablers);
}
bool ram_block_discard_is_required(void)
{
- return qatomic_read(&ram_block_discard_disabled) < 0;
+ return qatomic_read(&ram_block_discard_requirers);
}
--
2.29.2
