From fe6824d12642b005c69123ecf8631f9b13553f8b Mon Sep 17 00:00:00 2001 From: Laurent Vivier Date: Tue, 28 Mar 2017 14:09:34 +0200 Subject: [PATCH] spapr: fix memory hot-unplugging If, once the kernel has booted, we try to remove a memory hotplugged while the kernel was not started, QEMU crashes on an assert: qemu-system-ppc64: hw/virtio/vhost.c:651: vhost_commit: Assertion `r >= 0' failed. ... #4 in vhost_commit #5 in memory_region_transaction_commit #6 in pc_dimm_memory_unplug #7 in spapr_memory_unplug #8 spapr_machine_device_unplug #9 in hotplug_handler_unplug #10 in spapr_lmb_release #11 in detach #12 in set_allocation_state #13 in rtas_set_indicator ... If we take a closer look to the guest kernel log, we can see when we try to unplug the memory: pseries-hotplug-mem: Attempting to hot-add 4 LMB(s) What happens: 1- The kernel has ignored the memory hotplug event because it was not started when it was generated. 2- When we hot-unplug the memory, QEMU starts to remove the memory, generates an hot-unplug event, and signals the kernel of the incoming new event 3- as the kernel is started, on the QEMU signal, it reads the event list, decodes the hotplug event and tries to finish the hotplugging. 4- QEMU receive the the hotplug notification while it is trying to hot-unplug the memory. This moves the memory DRC to an invalid state This patch prevents this by not allowing to set the allocation state to USABLE while the DRC is awaiting release. RHBZ: https://bugzilla.redhat.com/show_bug.cgi?id=1432382 Signed-off-by: Laurent Vivier Signed-off-by: David Gibson --- hw/ppc/spapr_drc.c | 20 +++++++++++++++++--- include/hw/ppc/spapr_drc.h | 1 + 2 files changed, 18 insertions(+), 3 deletions(-) diff --git a/hw/ppc/spapr_drc.c b/hw/ppc/spapr_drc.c index 150f6bf2c7..a1cdc875b1 100644 --- a/hw/ppc/spapr_drc.c +++ b/hw/ppc/spapr_drc.c @@ -135,6 +135,17 @@ static uint32_t set_allocation_state(sPAPRDRConnector *drc, if (!drc->dev) { return RTAS_OUT_NO_SUCH_INDICATOR; } + if (drc->awaiting_release && drc->awaiting_allocation) { + /* kernel is acknowledging a previous hotplug event + * while we are already removing it. + * it's safe to ignore awaiting_allocation here since we know the + * situation is predicated on the guest either already having done + * so (boot-time hotplug), or never being able to acquire in the + * first place (hotplug followed by immediate unplug). + */ + drc->awaiting_allocation_skippable = true; + return RTAS_OUT_NO_SUCH_INDICATOR; + } } if (drc->type != SPAPR_DR_CONNECTOR_TYPE_PCI) { @@ -436,9 +447,11 @@ static void detach(sPAPRDRConnector *drc, DeviceState *d, } if (drc->awaiting_allocation) { - drc->awaiting_release = true; - trace_spapr_drc_awaiting_allocation(get_index(drc)); - return; + if (!drc->awaiting_allocation_skippable) { + drc->awaiting_release = true; + trace_spapr_drc_awaiting_allocation(get_index(drc)); + return; + } } drc->indicator_state = SPAPR_DR_INDICATOR_STATE_INACTIVE; @@ -448,6 +461,7 @@ static void detach(sPAPRDRConnector *drc, DeviceState *d, } drc->awaiting_release = false; + drc->awaiting_allocation_skippable = false; g_free(drc->fdt); drc->fdt = NULL; drc->fdt_start_offset = 0; diff --git a/include/hw/ppc/spapr_drc.h b/include/hw/ppc/spapr_drc.h index fa531d5c26..5524247cdc 100644 --- a/include/hw/ppc/spapr_drc.h +++ b/include/hw/ppc/spapr_drc.h @@ -154,6 +154,7 @@ typedef struct sPAPRDRConnector { bool awaiting_release; bool signalled; bool awaiting_allocation; + bool awaiting_allocation_skippable; /* device pointer, via link property */ DeviceState *dev; -- 2.11.4.GIT