>From abbe3b57af6a28bb81e5fb8b09b10802a8ccc3fe Mon Sep 17 00:00:00 2001
From: Dor Laor <dor@xxxxxxxxxx>
Date: Wed, 15 Jul 2009 17:53:16 +0300
Subject: [PATCH] Fix 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.
It is solved by checking for write-readiness using select.
Note that I check for select only for full 8 byte write and not
for partial writes. This is because we'll break the reader otherwise.
Signed-off-by: Dor Laor <dor@xxxxxxxxxx>
---
qemu-kvm.c | 16 ++++++++++++++++
1 files changed, 16 insertions(+), 0 deletions(-)
diff --git a/qemu-kvm.c b/qemu-kvm.c
index ed7e466..0ea67a7 100644
--- a/qemu-kvm.c
+++ b/qemu-kvm.c
@@ -2094,12 +2094,28 @@ void qemu_kvm_notify_work(void)
uint64_t value = 1;
char buffer[8];
size_t offset = 0;
+ fd_set wfds;
+ struct timeval tv;
+ int retval;
if (io_thread_fd == -1)
return;
memcpy(buffer, &value, sizeof(value));
+ FD_ZERO(&wfds);
+ FD_SET(io_thread_fd, &wfds);
+ tv.tv_sec = tv.tv_usec = 0;
+ retval = select(io_thread_fd + 1, NULL, &wfds, NULL, &tv);
+ if (retval == -1) {
+ fprintf(stderr, "failed to notify io thread due to select error\n");
+ return;
+ } else if (retval == 0)
+ /* We probably ponded this pipe too much and it is full now */
+ return;
+
+ assert(FD_ISSET(io_thread_fd, &wfds));
+
while (offset < 8) {
ssize_t len;
--
1.6.2.5
