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authorRoman Kagan <rkagan@virtuozzo.com>2019-05-23 10:54:48 +0000
committerPaolo Bonzini <pbonzini@redhat.com>2019-08-20 17:26:22 +0200
commite533f45d7dd85d6514de3f7a433f7dc4313e8f62 (patch)
treed9884ed20f33cec928d46d9e4381f86b36b1b84e /cpus-common.c
parent9e9b10c6491153b60ccfd021328f1f88e1669550 (diff)
cpus-common: nuke finish_safe_work
It was introduced in commit ab129972c8b41e15b0521895a46fd9c752b68a5e, with the following motivation: Because start_exclusive uses CPU_FOREACH, merge exclusive_lock with qemu_cpu_list_lock: together with a call to exclusive_idle (via cpu_exec_start/end) in cpu_list_add, this protects exclusive work against concurrent CPU addition and removal. However, it seems to be redundant, because the cpu-exclusive infrastructure provides suffificent protection against the newly added CPU starting execution while the cpu-exclusive work is running, and the aforementioned traversing of the cpu list is protected by qemu_cpu_list_lock. Besides, this appears to be the only place where the cpu-exclusive section is entered with the BQL taken, which has been found to trigger AB-BA deadlock as follows: vCPU thread main thread ----------- ----------- async_safe_run_on_cpu(self, async_synic_update) ... [cpu hot-add] process_queued_cpu_work() qemu_mutex_unlock_iothread() [grab BQL] start_exclusive() cpu_list_add() async_synic_update() finish_safe_work() qemu_mutex_lock_iothread() cpu_exec_start() So remove it. This paves the way to establishing a strict nesting rule of never entering the exclusive section with the BQL taken. Signed-off-by: Roman Kagan <rkagan@virtuozzo.com> Message-Id: <20190523105440.27045-2-rkagan@virtuozzo.com>
Diffstat (limited to 'cpus-common.c')
-rw-r--r--cpus-common.c8
1 files changed, 0 insertions, 8 deletions
diff --git a/cpus-common.c b/cpus-common.c
index 3ca58c64e8..023cfebfa3 100644
--- a/cpus-common.c
+++ b/cpus-common.c
@@ -69,12 +69,6 @@ static int cpu_get_free_index(void)
return cpu_index;
}
-static void finish_safe_work(CPUState *cpu)
-{
- cpu_exec_start(cpu);
- cpu_exec_end(cpu);
-}
-
void cpu_list_add(CPUState *cpu)
{
qemu_mutex_lock(&qemu_cpu_list_lock);
@@ -86,8 +80,6 @@ void cpu_list_add(CPUState *cpu)
}
QTAILQ_INSERT_TAIL_RCU(&cpus, cpu, node);
qemu_mutex_unlock(&qemu_cpu_list_lock);
-
- finish_safe_work(cpu);
}
void cpu_list_remove(CPUState *cpu)