On Fri, Jul 17, 2009 at 01:18:58AM +0300, Dor Laor wrote:
> 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]);
Applied, thanks.
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