* Lidong Chen (jemmy858...@gmail.com) wrote:
> From: Lidong Chen <jemmy858...@gmail.com>
>
> The channel_close maybe invoked by different threads. For example, source
> qemu invokes qemu_fclose in main thread, migration thread and return path
> thread. Destination qemu invokes qemu_fclose in main thread, listen thread
> and COLO incoming thread.
>
> Add a mutex in QEMUFile struct to avoid concurrent invoke channel_close.
>
> Signed-off-by: Lidong Chen <lidongc...@tencent.com>
> ---
> migration/qemu-file.c | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/migration/qemu-file.c b/migration/qemu-file.c
> index 977b9ae..87d0f05 100644
> --- a/migration/qemu-file.c
> +++ b/migration/qemu-file.c
> @@ -52,6 +52,7 @@ struct QEMUFile {
> unsigned int iovcnt;
>
> int last_error;
> + QemuMutex lock;
That could do with a comment saying what you're protecting
> };
>
> /*
> @@ -96,6 +97,7 @@ QEMUFile *qemu_fopen_ops(void *opaque, const QEMUFileOps
> *ops)
>
> f = g_new0(QEMUFile, 1);
>
> + qemu_mutex_init(&f->lock);
> f->opaque = opaque;
> f->ops = ops;
> return f;
> @@ -328,7 +330,9 @@ int qemu_fclose(QEMUFile *f)
> ret = qemu_file_get_error(f);
>
> if (f->ops->close) {
> + qemu_mutex_lock(&f->lock);
> int ret2 = f->ops->close(f->opaque);
> + qemu_mutex_unlock(&f->lock);
OK, and at least for the RDMA code, if it calls
close a 2nd time, rioc->rdma is checked so it wont actually free stuff a
2nd time.
> if (ret >= 0) {
> ret = ret2;
> }
> @@ -339,6 +343,7 @@ int qemu_fclose(QEMUFile *f)
> if (f->last_error) {
> ret = f->last_error;
> }
> + qemu_mutex_destroy(&f->lock);
> g_free(f);
Hmm but that's not safe; if two things really do call qemu_fclose()
on the same structure they race here and can end up destroying the lock
twice, or doing f->lock after the 1st one has already g_free(f).
So lets go back a step.
I think:
a) There should always be a separate QEMUFile* for
to_src_file and from_src_file - I don't see where you open
the 2nd one; I don't see your implementation of
f->ops->get_return_path.
b) I *think* that while the different threads might all call
fclose(), I think there should only ever be one qemu_fclose
call for each direction on the QEMUFile.
But now we have two problems:
If (a) is true then f->lock is separate on each one so
doesn't really protect if the two directions are closed
at once. (Assuming (b) is true)
If (a) is false and we actually share a single QEMUFile then
that race at the end happens.
Dave
> trace_qemu_file_fclose();
> return ret;
> --
> 1.8.3.1
>
--
Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
