From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:53712) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZfP0n-0008Jo-M0 for qemu-devel@nongnu.org; Fri, 25 Sep 2015 05:09:55 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ZfP0j-0003bJ-JW for qemu-devel@nongnu.org; Fri, 25 Sep 2015 05:09:49 -0400 Received: from mailhub.sw.ru ([195.214.232.25]:44568 helo=relay.sw.ru) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZfP0j-0003ah-6D for qemu-devel@nongnu.org; Fri, 25 Sep 2015 05:09:45 -0400 From: "Denis V. Lunev" Date: Fri, 25 Sep 2015 12:09:38 +0300 Message-Id: <1443172180-1005-1-git-send-email-den@openvz.org> In-Reply-To: <56050489.9010306@cn.fujitsu.com> References: <56050489.9010306@cn.fujitsu.com> Subject: [Qemu-devel] [PATCH v2 0/2] migration: fix deadlock List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Igor Redko , Juan Quintela , Anna Melekhova , qemu-devel@nongnu.org, Amit Shah , "Denis V. Lunev" Release qemu global mutex before call synchronize_rcu(). synchronize_rcu() waiting for all readers to finish their critical sections. There is at least one critical section in which we try to get QGM (critical section is in address_space_rw() and prepare_mmio_access() is trying to aquire QGM). Both functions (migration_end() and migration_bitmap_extend()) are called from main thread which is holding QGM. Thus there is a race condition that ends up with deadlock: main thread working thread Lock QGA | | Call KVM_EXIT_IO handler | | | Open rcu reader's critical section Migration cleanup bh | | | synchronize_rcu() is | waiting for readers | | prepare_mmio_access() is waiting for QGM \ / deadlock Patches here are quick and dirty, compile-tested only to validate the architectual approach. Igor, Anna, can you pls start your tests with these patches instead of your original one. Thank you. Signed-off-by: Denis V. Lunev CC: Igor Redko CC: Anna Melekhova CC: Juan Quintela CC: Amit Shah Denis V. Lunev (2): migration: bitmap_set is unnecessary as bitmap_new uses g_try_malloc0 migration: fix deadlock migration/ram.c | 45 ++++++++++++++++++++++++++++----------------- 1 file changed, 28 insertions(+), 17 deletions(-) -- 2.1.4