It replaces the previous fix of using select.
>From ab5ae4bb69f8ab6c9a476f7823cb8d6729d31594 Mon Sep 17 00:00:00 2001
From: Dor Laor <dor@xxxxxxxxxx>
Date: Wed, 15 Jul 2009 17:53:16 +0300
Subject: [PATCH] Set the iothread's eventfd/pipe descriptors to non-blocking.
It fixes migration issue when the destination is loaded.
If the migration socket is full, we get EAGAIN for the write.
The set_fd_handler2 defers the write for later on. The function
tries to wake up the iothread by qemu_kvm_notify_work.
Since this happens in a loop, multiple times, the pipe that emulates eventfd
becomes full and we get a deadlock.
Mark McLoughlin suggested to remove spurious wake-up of the migration code
when we get EAGAIN and wait for the socket to become writeable. (+1)
Nevertheless, the pipe descriptors shouldn't be blocking and the reader can
also read several chunks in a time.
Signed-off-by: Dor Laor <dor@xxxxxxxxxx>
---
qemu-kvm.c | 24 ++++++++++++++----------
1 files changed, 14 insertions(+), 10 deletions(-)
diff --git a/qemu-kvm.c b/qemu-kvm.c
index ed7e466..68a453c 100644
--- a/qemu-kvm.c
+++ b/qemu-kvm.c
@@ -2107,14 +2107,17 @@ void qemu_kvm_notify_work(void)
if (len == -1 && errno == EINTR)
continue;
- if (len <= 0)
+ /* In case we have a pipe, there is not reason to insist writing
+ * 8 bytes
+ */
+ if (len == -1 && errno == EAGAIN)
break;
+ if (len <= 0)
+ break;
+
offset += len;
}
-
- if (offset != 8)
- fprintf(stderr, "failed to notify io thread\n");
}
/* If we have signalfd, we mask out the signals we want to handle and then
@@ -2153,20 +2156,18 @@ static void sigfd_handler(void *opaque)
static void io_thread_wakeup(void *opaque)
{
int fd = (unsigned long)opaque;
- char buffer[8];
- size_t offset = 0;
+ char buffer[4096];
- while (offset < 8) {
+ /* Drain the pipe/(eventfd) */
+ while (1) {
ssize_t len;
- len = read(fd, buffer + offset, 8 - offset);
+ len = read(fd, buffer, sizeof(buffer));
if (len == -1 && errno == EINTR)
continue;
if (len <= 0)
break;
-
- offset += len;
}
}
@@ -2184,6 +2185,9 @@ int kvm_main_loop(void)
return -errno;
}
+ fcntl(fds[0], F_SETFL, O_NONBLOCK);
+ fcntl(fds[1], F_SETFL, O_NONBLOCK);
+
qemu_set_fd_handler2(fds[0], NULL, io_thread_wakeup, NULL,
(void *)(unsigned long)fds[0]);
--
1.6.2.5
