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From 14279ae97888ecd51bcf04771d064fa11a3df7a1 Mon Sep 17 00:00:00 2001
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From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
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Date: Wed, 20 Dec 2017 12:29:52 +0100
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Subject: [PATCH 02/42] block: avoid recursive AioContext acquire in
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bdrv_inactivate_all()
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RH-Author: Dr. David Alan Gilbert <dgilbert@redhat.com>
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Message-id: <20171220122952.9799-2-dgilbert@redhat.com>
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Patchwork-id: 78418
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O-Subject: [RHEL-7.5 qemu-kvm-rhev PATCH 1/1] block: avoid recursive AioContext acquire in bdrv_inactivate_all()
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Bugzilla: 1520824
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RH-Acked-by: Paolo Bonzini <pbonzini@redhat.com>
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RH-Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
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RH-Acked-by: Laurent Vivier <lvivier@redhat.com>
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From: Paolo Bonzini <pbonzini@redhat.com>
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BDRV_POLL_WHILE() does not support recursive AioContext locking. It
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only releases the AioContext lock once regardless of how many times the
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caller has acquired it. This results in a hang since the IOThread does
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not make progress while the AioContext is still locked.
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The following steps trigger the hang:
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$ qemu-system-x86_64 -M accel=kvm -m 1G -cpu host \
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-object iothread,id=iothread0 \
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-device virtio-scsi-pci,iothread=iothread0 \
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-drive if=none,id=drive0,file=test.img,format=raw \
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-device scsi-hd,drive=drive0 \
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-drive if=none,id=drive1,file=test.img,format=raw \
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-device scsi-hd,drive=drive1
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$ qemu-system-x86_64 ...same options... \
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-incoming tcp::1234
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(qemu) migrate tcp:127.0.0.1:1234
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...hang...
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Tested-by: Stefan Hajnoczi <stefanha@redhat.com>
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Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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Reviewed-by: Eric Blake <eblake@redhat.com>
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Message-id: 20171207201320.19284-2-stefanha@redhat.com
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Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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(cherry picked from commit bd6458e410c1e7d2912357aeb399fe7d8ee9f9a3)
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Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
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---
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block.c | 14 +++++++++++---
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1 file changed, 11 insertions(+), 3 deletions(-)
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diff --git a/block.c b/block.c
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index bc8b80b..b5736dd 100644
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--- a/block.c
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+++ b/block.c
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@@ -4221,9 +4221,15 @@ int bdrv_inactivate_all(void)
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BdrvNextIterator it;
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int ret = 0;
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int pass;
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+ GSList *aio_ctxs = NULL, *ctx;
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for (bs = bdrv_first(&it); bs; bs = bdrv_next(&it)) {
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- aio_context_acquire(bdrv_get_aio_context(bs));
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+ AioContext *aio_context = bdrv_get_aio_context(bs);
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+
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+ if (!g_slist_find(aio_ctxs, aio_context)) {
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+ aio_ctxs = g_slist_prepend(aio_ctxs, aio_context);
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+ aio_context_acquire(aio_context);
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+ }
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}
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/* We do two passes of inactivation. The first pass calls to drivers'
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@@ -4240,9 +4246,11 @@ int bdrv_inactivate_all(void)
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}
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out:
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- for (bs = bdrv_first(&it); bs; bs = bdrv_next(&it)) {
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- aio_context_release(bdrv_get_aio_context(bs));
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+ for (ctx = aio_ctxs; ctx != NULL; ctx = ctx->next) {
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+ AioContext *aio_context = ctx->data;
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+ aio_context_release(aio_context);
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}
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+ g_slist_free(aio_ctxs);
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return ret;
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}
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--
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1.8.3.1
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