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