From c8856d5cbcf3d427cd02c9556f845486ab5362bc Mon Sep 17 00:00:00 2001
From: Dietmar Maurer <dietmar@proxmox.com>
Date: Fri, 14 Feb 2020 12:37:27 +0100
Subject: [PATCH qemu 3/7] PVE backup: move backup_state.cancel to
 backup_state.stat.cancel

In order to avoid lock contention with qmp_backup_cancel.
---
 blockdev.c | 25 +++++++++++++++----------
 1 file changed, 15 insertions(+), 10 deletions(-)

diff --git a/blockdev.c b/blockdev.c
index 2f84f8832d..a4b5b98224 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -3204,9 +3204,9 @@ static void block_on_coroutine_fn(CoroutineEntry *entry, void *entry_arg)
     AIO_WAIT_WHILE(ctx, !wrapper.finished);
 }
 
-
 static struct PVEBackupState {
     struct {
+        // Everithing accessed from qmp command, protected using rwlock
         CoRwlock rwlock;
         Error *error;
         time_t start_time;
@@ -3217,8 +3217,8 @@ static struct PVEBackupState {
         size_t total;
         size_t transferred;
         size_t zero_bytes;
+        bool cancel;
     } stat;
-    bool cancel;
     int64_t speed;
     VmaWriter *vmaw;
     GList *di_list;
@@ -3247,13 +3247,16 @@ static int coroutine_fn pvebackup_co_dump_cb(void *opaque, BlockBackend *target,
     const unsigned char *buf = pbuf;
     PVEBackupDevInfo *di = opaque;
 
-    qemu_co_mutex_lock(&backup_state.backup_mutex);
+    qemu_co_rwlock_rdlock(&backup_state.stat.rwlock);
+    bool cancel = backup_state.stat.cancel;
+    qemu_co_rwlock_unlock(&backup_state.stat.rwlock);
 
-    if (backup_state.cancel) {
-        qemu_co_mutex_unlock(&backup_state.backup_mutex);
+    if (cancel) {
         return size; // return success
     }
 
+    qemu_co_mutex_lock(&backup_state.backup_mutex);
+
     uint64_t cluster_num = start / VMA_CLUSTER_SIZE;
     if ((cluster_num * VMA_CLUSTER_SIZE) != start) {
         qemu_co_rwlock_rdlock(&backup_state.stat.rwlock);
@@ -3419,9 +3422,11 @@ static void coroutine_fn pvebackup_co_cancel(void *opaque)
 {
     assert(qemu_in_coroutine());
 
-    qemu_co_mutex_lock(&backup_state.backup_mutex);
+    qemu_co_rwlock_wrlock(&backup_state.stat.rwlock);
+    backup_state.stat.cancel = true;
+    qemu_co_rwlock_unlock(&backup_state.stat.rwlock);
 
-    backup_state.cancel = true;
+    qemu_co_mutex_lock(&backup_state.backup_mutex);
 
     // Avoid race between block jobs and backup-cancel command:
     if (!backup_state.vmaw) {
@@ -3542,7 +3547,7 @@ static void coroutine_fn pvebackup_co_run_next_job(void)
 
                     if (job_should_pause(&job->job)) {
                         qemu_co_rwlock_rdlock(&backup_state.stat.rwlock);
-                        bool error_or_canceled = backup_state.stat.error || backup_state.cancel;
+                        bool error_or_canceled = backup_state.stat.error || backup_state.stat.cancel;
                         qemu_co_rwlock_unlock(&backup_state.stat.rwlock);
 
                         if (error_or_canceled) {
@@ -3761,10 +3766,10 @@ static void coroutine_fn pvebackup_co_start(void *opaque)
     }
     /* initialize global backup_state now */
 
-    backup_state.cancel = false;
-
     qemu_co_rwlock_wrlock(&backup_state.stat.rwlock);
 
+    backup_state.stat.cancel = false;
+
     if (backup_state.stat.error) {
         error_free(backup_state.stat.error);
         backup_state.stat.error = NULL;
-- 
2.20.1