From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:46111) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1eQwXQ-0007BK-61 for qemu-devel@nongnu.org; Mon, 18 Dec 2017 09:37:05 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1eQwXP-0007az-BA for qemu-devel@nongnu.org; Mon, 18 Dec 2017 09:37:04 -0500 Received: from mx1.redhat.com ([209.132.183.28]:60566) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1eQwXP-0007Zk-4c for qemu-devel@nongnu.org; Mon, 18 Dec 2017 09:37:03 -0500 From: Stefan Hajnoczi Date: Mon, 18 Dec 2017 14:35:25 +0000 Message-Id: <20171218143530.12082-19-stefanha@redhat.com> In-Reply-To: <20171218143530.12082-1-stefanha@redhat.com> References: <20171218143530.12082-1-stefanha@redhat.com> Subject: [Qemu-devel] [PULL 18/23] block: avoid recursive AioContext acquire in bdrv_inactivate_all() List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: Peter Maydell , Paolo Bonzini , Stefan Hajnoczi 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 --- block.c | 14 +++++++++++--- 1 file changed, 11 insertions(+), 3 deletions(-) diff --git a/block.c b/block.c index 9a1a0d1e73..1c37ce4554 100644 --- a/block.c +++ b/block.c @@ -4320,9 +4320,15 @@ 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' @@ -4340,9 +4346,11 @@ 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; } -- 2.14.3