From 8649f2f9b2d83b627199babc52b454db136e253c Mon Sep 17 00:00:00 2001 From: Stefan Hajnoczi Date: Mon, 22 May 2017 14:57:04 +0100 Subject: [PATCH] migration: use bdrv_drain_all_begin/end() instead bdrv_drain_all() blk/bdrv_drain_all() only takes effect for a single instant and then resumes block jobs, guest devices, and other external clients like the NBD server. This can be handy when performing a synchronous drain before terminating the program, for example. Monitor commands usually need to quiesce I/O across an entire code region so blk/bdrv_drain_all() is not suitable. They must use bdrv_drain_all_begin/end() to mark the region. This prevents new I/O requests from slipping in or worse - block jobs completing and modifying the graph. I audited other blk/bdrv_drain_all() callers but did not find anything that needs a similar fix. This patch fixes the savevm/loadvm commands. Although I haven't encountered a read world issue this makes the code safer. Suggested-by: Kevin Wolf Signed-off-by: Stefan Hajnoczi Reviewed-by: Eric Blake Signed-off-by: Kevin Wolf --- migration/savevm.c | 18 +++++++++++++++--- 1 file changed, 15 insertions(+), 3 deletions(-) diff --git a/migration/savevm.c b/migration/savevm.c index 5846d9c369..b08df04d59 100644 --- a/migration/savevm.c +++ b/migration/savevm.c @@ -2107,6 +2107,8 @@ int save_snapshot(const char *name, Error **errp) } vm_stop(RUN_STATE_SAVE_VM); + bdrv_drain_all_begin(); + aio_context_acquire(aio_context); memset(sn, 0, sizeof(*sn)); @@ -2165,6 +2167,9 @@ int save_snapshot(const char *name, Error **errp) if (aio_context) { aio_context_release(aio_context); } + + bdrv_drain_all_end(); + if (saved_vm_running) { vm_start(); } @@ -2273,20 +2278,21 @@ int load_snapshot(const char *name, Error **errp) } /* Flush all IO requests so they don't interfere with the new state. */ - bdrv_drain_all(); + bdrv_drain_all_begin(); ret = bdrv_all_goto_snapshot(name, &bs); if (ret < 0) { error_setg(errp, "Error %d while activating snapshot '%s' on '%s'", ret, name, bdrv_get_device_name(bs)); - return ret; + goto err_drain; } /* restore the VM state */ f = qemu_fopen_bdrv(bs_vm_state, 0); if (!f) { error_setg(errp, "Could not open VM state file"); - return -EINVAL; + ret = -EINVAL; + goto err_drain; } qemu_system_reset(SHUTDOWN_CAUSE_NONE); @@ -2296,6 +2302,8 @@ int load_snapshot(const char *name, Error **errp) ret = qemu_loadvm_state(f); aio_context_release(aio_context); + bdrv_drain_all_end(); + migration_incoming_state_destroy(); if (ret < 0) { error_setg(errp, "Error %d while loading VM state", ret); @@ -2303,6 +2311,10 @@ int load_snapshot(const char *name, Error **errp) } return 0; + +err_drain: + bdrv_drain_all_end(); + return ret; } void vmstate_register_ram(MemoryRegion *mr, DeviceState *dev)