| Message ID | 20170519103247.4405-5-stefanha@redhat.com |
|---|---|
| State | New |
| Headers | show |
Am 19.05.2017 um 12:32 hat Stefan Hajnoczi geschrieben: > 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 <kwolf@redhat.com> > Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com> > @@ -2279,7 +2284,7 @@ int load_vmstate(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) { > @@ -2303,6 +2308,8 @@ int load_vmstate(const char *name, Error **errp) > qemu_fclose(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); There are a few error returns between these two places where a bdrv_drain_all_end() is missing. Kevin
On Mon, May 22, 2017 at 02:17:35PM +0200, Kevin Wolf wrote: > Am 19.05.2017 um 12:32 hat Stefan Hajnoczi geschrieben: > > 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 <kwolf@redhat.com> > > Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com> > > > @@ -2279,7 +2284,7 @@ int load_vmstate(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) { > > @@ -2303,6 +2308,8 @@ int load_vmstate(const char *name, Error **errp) > > qemu_fclose(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); > > There are a few error returns between these two places where a > bdrv_drain_all_end() is missing. Thank you, will fix in the next revision. Stefan
diff --git a/migration/savevm.c b/migration/savevm.c index 3ca319f..f134e48 100644 --- a/migration/savevm.c +++ b/migration/savevm.c @@ -2113,6 +2113,8 @@ int save_vmstate(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)); @@ -2171,6 +2173,9 @@ int save_vmstate(const char *name, Error **errp) if (aio_context) { aio_context_release(aio_context); } + + bdrv_drain_all_end(); + if (saved_vm_running) { vm_start(); } @@ -2279,7 +2284,7 @@ int load_vmstate(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) { @@ -2303,6 +2308,8 @@ int load_vmstate(const char *name, Error **errp) qemu_fclose(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);
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 <kwolf@redhat.com> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com> --- migration/savevm.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-)