From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:33402) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1b17Vu-00085m-9X for qemu-devel@nongnu.org; Fri, 13 May 2016 03:27:59 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1b17Vp-0008Qw-4w for qemu-devel@nongnu.org; Fri, 13 May 2016 03:27:57 -0400 Received: from mailhub.sw.ru ([195.214.232.25]:27022 helo=relay.sw.ru) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1b17Vo-0008KV-MS for qemu-devel@nongnu.org; Fri, 13 May 2016 03:27:53 -0400 From: "Denis V. Lunev" Date: Fri, 13 May 2016 10:27:01 +0300 Message-Id: <1463124421-16587-1-git-send-email-den@openvz.org> Subject: [Qemu-devel] [PATCH 1/1] migration: fix ram decompression race deadlock List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: den@openvz.org, Maxim Nestratov , Juan Quintela , Amit Shah From: Maxim Nestratov There is a race in between do_data_decompress and start_decompression. do_data_decompress() while (!quit_decomp_thread) { qemu_mutex_lock(¶m->mutex); while (!param->start && !quit_decomp_thread) { qemu_cond_wait(¶m->cond, ¶m->mutex); ... param->start = false; } qemu_mutex_unlock(¶m->mutex); [ preempted here, start_decompression() is executed ] } start_decompression() { qemu_mutex_lock(¶m->mutex); param->start = true; qemu_cond_signal(¶m->cond); qemu_mutex_unlock(¶m->mutex); } In this case do_data_decompress will never enter inner loop again and will eat 100% CPU. The patch fixes this problem by correcting while loop where we wait for condition only and other actions are moved out of it. Signed-off-by: Maxim Nestratov Signed-off-by: Denis V. Lunev CC: Juan Quintela CC: Amit Shah --- migration/ram.c | 22 +++++++++++----------- 1 file changed, 11 insertions(+), 11 deletions(-) diff --git a/migration/ram.c b/migration/ram.c index 3f05738..579bfc0 100644 --- a/migration/ram.c +++ b/migration/ram.c @@ -2193,18 +2193,18 @@ static void *do_data_decompress(void *opaque) qemu_mutex_lock(¶m->mutex); while (!param->start && !quit_decomp_thread) { qemu_cond_wait(¶m->cond, ¶m->mutex); - pagesize = TARGET_PAGE_SIZE; - if (!quit_decomp_thread) { - /* uncompress() will return failed in some case, especially - * when the page is dirted when doing the compression, it's - * not a problem because the dirty page will be retransferred - * and uncompress() won't break the data in other pages. - */ - uncompress((Bytef *)param->des, &pagesize, - (const Bytef *)param->compbuf, param->len); - } - param->start = false; } + pagesize = TARGET_PAGE_SIZE; + if (!quit_decomp_thread) { + /* uncompress() will return failed in some case, especially + * when the page is dirted when doing the compression, it's + * not a problem because the dirty page will be retransferred + * and uncompress() won't break the data in other pages. + */ + uncompress((Bytef *)param->des, &pagesize, + (const Bytef *)param->compbuf, param->len); + } + param->start = false; qemu_mutex_unlock(¶m->mutex); } -- 2.1.4