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Re: [Qemu-devel] [PATCH v2] Fix segfault on migration completion
From: |
Markus Armbruster |
Subject: |
Re: [Qemu-devel] [PATCH v2] Fix segfault on migration completion |
Date: |
Mon, 31 Oct 2011 07:15:25 +0100 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/23.2 (gnu/linux) |
Luiz Capitulino <address@hidden> writes:
> A simple migration reproduces it:
>
> 1. Start the source VM with:
>
> # qemu [...] -S
>
> 2. Start the destination VM with:
>
> # qemu <source VM cmd-line> -incoming tcp:0:4444
>
> 3. In the source VM:
>
> (qemu) migrate -d tcp:0:4444
>
> 4. The source VM will segfault as soon as migration completes (might not
> happen in the first try)
>
> What is happening here is that qemu_file_put_notify() can end up closing
> 's->file' (in which case it's also set to NULL). The call stack is rather
> complex, but Eduardo helped tracking it to:
>
> select loop -> migrate_fd_put_notify() -> qemu_file_put_notify() ->
> buffered_put_buffer() -> migrate_fd_put_ready() ->
> migrate_fd_completed() -> migrate_fd_cleanup().
>
> To be honest, it's not completely clear to me in which cases 's->file'
> is not closed (on error maybe)? But I doubt this fix will make anything
> worse.
>
> Reviewed-by: Paolo Bonzini <address@hidden>
> Acked-by: Eduardo Habkost <address@hidden>
> Signed-off-by: Luiz Capitulino <address@hidden>
> ---
>
> V2: better commit log
>
> migration.c | 2 +-
> 1 files changed, 1 insertions(+), 1 deletions(-)
>
> diff --git a/migration.c b/migration.c
> index bdca72e..f6e6208 100644
> --- a/migration.c
> +++ b/migration.c
> @@ -252,7 +252,7 @@ static void migrate_fd_put_notify(void *opaque)
>
> qemu_set_fd_handler2(s->fd, NULL, NULL, NULL, NULL);
> qemu_file_put_notify(s->file);
> - if (qemu_file_get_error(s->file)) {
> + if (s->file && qemu_file_get_error(s->file)) {
> migrate_fd_error(s);
> }
> }
I wonder whether we can lose the error in s->file by closing s->file
before we get here. But even if we can, we still report more errors
than before the series this patch fixes.