On Wed, Jul 12, 2017 at 12:00:22PM +0100, Dr. David Alan Gilbert wrote: > * Peter Xu (pet...@redhat.com) wrote: > > On Tue, Jul 04, 2017 at 07:49:12PM +0100, Dr. David Alan Gilbert (git) > > wrote: > > > From: "Dr. David Alan Gilbert" <dgilb...@redhat.com> > > > > > > Closing the file before exit on a failure allows > > > the source to cleanup better, especially with RDMA. > > > > > > Partial fix for https://bugs.launchpad.net/qemu/+bug/1545052 > > > > In above bug reported, the issue is that both dst and src VMs hanged > > when migration failed (which is a by-design failure). On destination, > > it hangs at (copied from the link): > > > > #0 0x00007ffff39141cd in write () at ../sysdeps/unix/syscall-template.S:81 > > #1 0x00007ffff27fe795 in rdma_get_cm_event.part.15 () from > > /lib64/librdmacm.so.1 > > #2 0x000055555593e445 in qemu_rdma_cleanup (rdma=0x7fff9647e010) at > > migration/rdma.c:2210 > > #3 0x000055555593ea45 in qemu_rdma_close (opaque=0x555557796770) at > > migration/rdma.c:2652 > > #4 0x00005555559397cc in qemu_fclose (f=f@entry=0x5555564b1450) at > > migration/qemu-file.c:270 > > #5 0x0000555555936b88 in process_incoming_migration_co > > (opaque=0x5555564b1450) at migration/migration.c:361 > > #6 0x0000555555a25a1a in coroutine_trampoline (i0=<optimized out>, > > i1=<optimized out>) at util/coroutine-ucontext.c:79 > > #7 0x00007fffef5b3110 in ?? () from /lib64/libc.so.6 > > > > So looks like at that time we have qemu_fclose() for the incoming fd, > > and that's the thing that caused trouble. > > I never saw that hang in the current world; I saw the source hang > rather than the destination. A hung destination is annoying but > since it's a failed migration anyway it's no big problem; the much > bigger problem is a failed migration which breaks the source. > > > (just to mention that the version caused failure is commit fc1ec1acf, > > which is mentioned in the first comment in the bz) > > > > Now the situation is: we don't have qemu_flose() now in current QEMU > > master on the failure path (see below, we just exit() directly). Then > > would the bz still valid now? And, if we apply this fix (then we do > > qemu_fclose() again), would it hang again instead of fixing anything? > > It doesn't seem to - but the big benefit we get from doing the close > is that we trigger the 'Early Error. Sending error.' case in > qemu_rdma_cleanup - by sending that error flag we cause the > received_error flag to be set on the source, and that causes the > migration to cleanly fail. > > Also, since it sets that received_error flag on the source, my patch 3/5 > would exit it's qemu_rdma_wait_comp_channel loop so theoretically the > other side of the hang seen in lp1545052 couldn't happen.
I see. Thanks. I see there is a new version of the series. Will reply in that thread. -- Peter Xu