Merge tag 'next-pull-request' of https://gitlab.com/juan.quintela/qemu into staging

Migration PULL request (take 3)

Hi

Drop everything that is not a bug fix:
- fixes by peter
- fix comment on block creation (me)
- fix return values from qio_channel_block()

Please, apply.

(take 1)
It includes:
- Leonardo fix for zero_copy flush
- Fiona fix for return value of readv/writev
- Peter Xu cleanups
- Peter Xu preempt patches
- Patches ready from zero page (me)
- AVX2 support (ling)
- fix for slow networking and reordering of first packets (manish)

Please, apply.

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# gpg: Good signature from "Juan Quintela <quintela@redhat.com>" [full]
# gpg:                 aka "Juan Quintela <quintela@trasno.org>" [full]
# Primary key fingerprint: 1899 FF8E DEBF 58CC EE03  4B82 F487 EF18 5872 D723

* tag 'next-pull-request' of https://gitlab.com/juan.quintela/qemu:
  migration: Block migration comment or code is wrong
  migration: Disable multifd explicitly with compression
  migration: Use non-atomic ops for clear log bitmap
  migration: Disallow postcopy preempt to be used with compress
  migration: Fix race on qemu_file_shutdown()
  migration: Fix possible infinite loop of ram save process
  migration/multifd/zero-copy: Create helper function for flushing
  migration/channel-block: fix return value for qio_channel_block_{readv,writev}

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

1 files changed, 24 insertions, 3 deletions

diff --git a/migration/qemu-file.c b/migration/qemu-file.c
index 4f400c2e52..2d5f74ffc2 100644
--- a/migration/qemu-file.c
+++ b/migration/qemu-file.c
@@ -79,6 +79,30 @@ int qemu_file_shutdown(QEMUFile *f)
     int ret = 0;
 
     f->shutdown = true;
+
+    /*
+     * We must set qemufile error before the real shutdown(), otherwise
+     * there can be a race window where we thought IO all went though
+     * (because last_error==NULL) but actually IO has already stopped.
+     *
+     * If without correct ordering, the race can happen like this:
+     *
+     *      page receiver                     other thread
+     *      -------------                     ------------
+     *      qemu_get_buffer()
+     *                                        do shutdown()
+     *        returns 0 (buffer all zero)
+     *        (we didn't check this retcode)
+     *      try to detect IO error
+     *        last_error==NULL, IO okay
+     *      install ALL-ZERO page
+     *                                        set last_error
+     *      --> guest crash!
+     */
+    if (!f->last_error) {
+        qemu_file_set_error(f, -EIO);
+    }
+
     if (!qio_channel_has_feature(f->ioc,
                                  QIO_CHANNEL_FEATURE_SHUTDOWN)) {
         return -ENOSYS;
@@ -88,9 +112,6 @@ int qemu_file_shutdown(QEMUFile *f)
         ret = -EIO;
     }
 
-    if (!f->last_error) {
-        qemu_file_set_error(f, -EIO);
-    }
     return ret;
 }