* 858585 jemmy (jemmy858...@gmail.com) wrote: > On Wed, May 9, 2018 at 2:40 AM, Dr. David Alan Gilbert > <dgilb...@redhat.com> wrote: > > * Lidong Chen (jemmy858...@gmail.com) wrote: > >> When cancel migration during RDMA precopy, the source qemu main thread > >> hangs sometime. > >> > >> The backtrace is: > >> (gdb) bt > >> #0 0x00007f249eabd43d in write () from /lib64/libpthread.so.0 > >> #1 0x00007f24a1ce98e4 in rdma_get_cm_event (channel=0x4675d10, > >> event=0x7ffe2f643dd0) at src/cma.c:2189 > >> #2 0x00000000007b6166 in qemu_rdma_cleanup (rdma=0x6784000) at > >> migration/rdma.c:2296 > >> #3 0x00000000007b7cae in qio_channel_rdma_close (ioc=0x3bfcc30, > >> errp=0x0) at migration/rdma.c:2999 > >> #4 0x00000000008db60e in qio_channel_close (ioc=0x3bfcc30, errp=0x0) > >> at io/channel.c:273 > >> #5 0x00000000007a8765 in channel_close (opaque=0x3bfcc30) at > >> migration/qemu-file-channel.c:98 > >> #6 0x00000000007a71f9 in qemu_fclose (f=0x527c000) at > >> migration/qemu-file.c:334 > >> #7 0x0000000000795b96 in migrate_fd_cleanup (opaque=0x3b46280) at > >> migration/migration.c:1162 > >> #8 0x000000000093a71b in aio_bh_call (bh=0x3db7a20) at util/async.c:90 > >> #9 0x000000000093a7b2 in aio_bh_poll (ctx=0x3b121c0) at > >> util/async.c:118 > >> #10 0x000000000093f2ad in aio_dispatch (ctx=0x3b121c0) at > >> util/aio-posix.c:436 > >> #11 0x000000000093ab41 in aio_ctx_dispatch (source=0x3b121c0, > >> callback=0x0, user_data=0x0) > >> at util/async.c:261 > >> #12 0x00007f249f73c7aa in g_main_context_dispatch () from > >> /lib64/libglib-2.0.so.0 > >> #13 0x000000000093dc5e in glib_pollfds_poll () at util/main-loop.c:215 > >> #14 0x000000000093dd4e in os_host_main_loop_wait (timeout=28000000) at > >> util/main-loop.c:263 > >> #15 0x000000000093de05 in main_loop_wait (nonblocking=0) at > >> util/main-loop.c:522 > >> #16 0x00000000005bc6a5 in main_loop () at vl.c:1944 > >> #17 0x00000000005c39b5 in main (argc=56, argv=0x7ffe2f6443f8, > >> envp=0x3ad0030) at vl.c:4752 > >> > >> It does not get the RDMA_CM_EVENT_DISCONNECTED event after rdma_disconnect > >> sometime. > >> I do not find out the root cause why not get RDMA_CM_EVENT_DISCONNECTED > >> event, but > >> it can be reproduced if not invoke ibv_dereg_mr to release all ram blocks > >> which fixed > >> in previous patch. > > > > Does this happen without your other changes? > > Yes, this issue also happen on v2.12.0. base on > commit 4743c23509a51bd4ee85cc272287a41917d1be35 > > > Can you give me instructions to repeat it and also say which > > cards you wereusing? > > This issue can be reproduced by start and cancel migration. > less than 10 times, this issue will be reproduced. > > The command line is: > virsh migrate --live --copy-storage-all --undefinesource --persistent > --timeout 10800 \ > --verbose 83e0049e-1325-4f31-baf9-25231509ada1 \ > qemu+ssh://9.16.46.142/system rdma://9.16.46.142 > > The net card i use is : > 0000:3b:00.0 Ethernet controller: Mellanox Technologies MT27710 Family > [ConnectX-4 Lx] > 0000:3b:00.1 Ethernet controller: Mellanox Technologies MT27710 Family > [ConnectX-4 Lx] > > This issue is related to ibv_dereg_mr, if not invoke ibv_dereg_mr for > all ram block, this issue can be reproduced. > If we fixed the bugs and use ibv_dereg_mr to release all ram block, > this issue never happens.
Maybe that is the right fix; I can imagine that the RDMA code doesn't like closing down if there are still ramblocks registered that potentially could have incoming DMA? > And for the kernel part, there is a bug also cause not release ram > block when canceling live migration. > https://patchwork.kernel.org/patch/10385781/ OK, that's a pain; which threads are doing the dereg - is some stuff in the migration thread and some stuff in the main thread on cleanup? Dave > > > >> Anyway, it should not invoke rdma_get_cm_event in main thread, and the > >> event channel > >> is also destroyed in qemu_rdma_cleanup. > >> > >> Signed-off-by: Lidong Chen <lidongc...@tencent.com> > >> --- > >> migration/rdma.c | 12 ++---------- > >> migration/trace-events | 1 - > >> 2 files changed, 2 insertions(+), 11 deletions(-) > >> > >> diff --git a/migration/rdma.c b/migration/rdma.c > >> index 0dd4033..92e4d30 100644 > >> --- a/migration/rdma.c > >> +++ b/migration/rdma.c > >> @@ -2275,8 +2275,7 @@ static int qemu_rdma_write(QEMUFile *f, RDMAContext > >> *rdma, > >> > >> static void qemu_rdma_cleanup(RDMAContext *rdma) > >> { > >> - struct rdma_cm_event *cm_event; > >> - int ret, idx; > >> + int idx; > >> > >> if (rdma->cm_id && rdma->connected) { > >> if ((rdma->error_state || > >> @@ -2290,14 +2289,7 @@ static void qemu_rdma_cleanup(RDMAContext *rdma) > >> qemu_rdma_post_send_control(rdma, NULL, &head); > >> } > >> > >> - ret = rdma_disconnect(rdma->cm_id); > >> - if (!ret) { > >> - trace_qemu_rdma_cleanup_waiting_for_disconnect(); > >> - ret = rdma_get_cm_event(rdma->channel, &cm_event); > >> - if (!ret) { > >> - rdma_ack_cm_event(cm_event); > >> - } > >> - } > >> + rdma_disconnect(rdma->cm_id); > > > > I'm worried whether this change could break stuff: > > The docs say for rdma_disconnect that it flushes any posted work > > requests to the completion queue; so unless we wait for the event > > do we know the stuff has been flushed? In the normal non-cancel case > > I'm worried that means we could lose something. > > (But I don't know the rdma/infiniband specs well enough to know if it's > > really a problem). > > In qemu_fclose function, it invoke qemu_fflush(f) before invoke f->ops->close. > so I think it's safe for normal migration case. > > For the root cause why not receive RDMA_CM_EVENT_DISCONNECTED event > after rdma_disconnect, > I loop in Aviad Yehezkel<avia...@mellanox.com>, Aviad will help us > find the root cause. > > > > > Dave > > > >> trace_qemu_rdma_cleanup_disconnect(); > >> rdma->connected = false; > >> } > >> diff --git a/migration/trace-events b/migration/trace-events > >> index d6be74b..64573ff 100644 > >> --- a/migration/trace-events > >> +++ b/migration/trace-events > >> @@ -125,7 +125,6 @@ qemu_rdma_accept_pin_state(bool pin) "%d" > >> qemu_rdma_accept_pin_verbsc(void *verbs) "Verbs context after listen: %p" > >> qemu_rdma_block_for_wrid_miss(const char *wcompstr, int wcomp, const char > >> *gcompstr, uint64_t req) "A Wanted wrid %s (%d) but got %s (%" PRIu64 ")" > >> qemu_rdma_cleanup_disconnect(void) "" > >> -qemu_rdma_cleanup_waiting_for_disconnect(void) "" > >> qemu_rdma_close(void) "" > >> qemu_rdma_connect_pin_all_requested(void) "" > >> qemu_rdma_connect_pin_all_outcome(bool pin) "%d" > >> -- > >> 1.8.3.1 > >> > > -- > > Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK -- Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK