72 lines
2.5 KiB
Diff
72 lines
2.5 KiB
Diff
From 28a204390093e5dfa0b4a2e94c06e807fe777c5f Mon Sep 17 00:00:00 2001
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From: Stefan Hajnoczi <stefanha@redhat.com>
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Date: Mon, 8 May 2017 14:07:05 -0400
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Subject: [PATCH 06/23] aio: add missing aio_notify() to aio_enable_external()
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The main loop uses aio_disable_external()/aio_enable_external() to
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temporarily disable processing of external AioContext clients like
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device emulation.
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This allows monitor commands to quiesce I/O and prevent the guest from
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submitting new requests while a monitor command is in progress.
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The aio_enable_external() API is currently broken when an IOThread is in
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aio_poll() waiting for fd activity when the main loop re-enables
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external clients. Incrementing ctx->external_disable_cnt does not wake
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the IOThread from ppoll(2) so fd processing remains suspended and leads
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to unresponsive emulated devices.
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This patch adds an aio_notify() call to aio_enable_external() so the
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IOThread is kicked out of ppoll(2) and will re-arm the file descriptors.
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The bug can be reproduced as follows:
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$ qemu -M accel=kvm -m 1024 \
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-object iothread,id=iothread0 \
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-device virtio-scsi-pci,iothread=iothread0,id=virtio-scsi-pci0 \
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-drive if=none,id=drive0,aio=native,cache=none,format=raw,file=test.img \
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-device scsi-hd,id=scsi-hd0,drive=drive0 \
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-qmp tcp::5555,server,nowait
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$ scripts/qmp/qmp-shell localhost:5555
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(qemu) blockdev-snapshot-sync device=drive0 snapshot-file=sn1.qcow2
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mode=absolute-paths format=qcow2
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After blockdev-snapshot-sync completes the SCSI disk will be
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unresponsive. This leads to request timeouts inside the guest.
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Reported-by: Qianqian Zhu <qizhu@redhat.com>
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Reviewed-by: Fam Zheng <famz@redhat.com>
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Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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Message-id: 20170508180705.20609-1-stefanha@redhat.com
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Suggested-by: Fam Zheng <famz@redhat.com>
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Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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---
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include/block/aio.h | 10 ++++++++--
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1 file changed, 8 insertions(+), 2 deletions(-)
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diff --git a/include/block/aio.h b/include/block/aio.h
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index 406e32305a..e9aeeaec94 100644
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--- a/include/block/aio.h
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+++ b/include/block/aio.h
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@@ -454,8 +454,14 @@ static inline void aio_disable_external(AioContext *ctx)
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*/
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static inline void aio_enable_external(AioContext *ctx)
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{
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- assert(ctx->external_disable_cnt > 0);
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- atomic_dec(&ctx->external_disable_cnt);
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+ int old;
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+
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+ old = atomic_fetch_dec(&ctx->external_disable_cnt);
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+ assert(old > 0);
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+ if (old == 1) {
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+ /* Kick event loop so it re-arms file descriptors */
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+ aio_notify(ctx);
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+ }
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}
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/**
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--
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2.11.0
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