From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753471AbdARVIS (ORCPT ); Wed, 18 Jan 2017 16:08:18 -0500 Received: from smtprelay0170.hostedemail.com ([216.40.44.170]:38890 "EHLO smtprelay.hostedemail.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1753278AbdARVIQ (ORCPT ); Wed, 18 Jan 2017 16:08:16 -0500 X-Session-Marker: 726F737465647440676F6F646D69732E6F7267 X-Spam-Summary: 2,0,0,,d41d8cd98f00b204,rostedt@goodmis.org,:::::,RULES_HIT:41:355:379:541:960:966:973:988:989:1260:1277:1311:1313:1314:1345:1437:1515:1516:1518:1534:1541:1593:1594:1711:1730:1747:1777:1792:2196:2199:2393:2559:2562:3138:3139:3140:3141:3142:3352:3622:3865:3866:3867:3868:3870:3871:3872:3874:4250:4385:5007:6119:6261:7875:7903:10004:10400:10848:11026:11232:11473:11658:11914:12043:12296:12438:12760:13069:13160:13229:13311:13357:13439:13972:14096:14097:14659:14721:14777:21080:21433:21451:30012:30022:30054:30066,0,RBL:none,CacheIP:none,Bayesian:0.5,0.5,0.5,Netcheck:none,DomainCache:0,MSF:not bulk,SPF:fn,MSBL:0,DNSBL:none,Custom_rules:0:0:0,LFtime:2,LUA_SUMMARY:none X-HE-Tag: crate16_f8b8a374fe01 X-Filterd-Recvd-Size: 2044 Date: Wed, 18 Jan 2017 15:58:24 -0500 From: Steven Rostedt To: Chris Wilson Cc: LKML , Peter Zijlstra Subject: __mutex_lock_common() unlikely very likely Message-ID: <20170118155824.689a9996@gandalf.local.home> X-Mailer: Claws Mail 3.14.0 (GTK+ 2.24.31; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Chris, My branch tracer flagged the unlikely in __mutex_lock_common() as always hit. That's the: if (use_ww_ctx) { [...] if (unlikely(ww_ctx == READ_ONCE(ww->ctx))) return -EALREADY; } This is hit 100% of the time, and its coming from the drm logic: for example: => drm_atomic_get_crtc_state => drm_atomic_helper_duplicate_state => intel_modeset_init => i915_driver_load => i915_pci_probe => local_pci_probe => pci_device_probe => driver_probe_device => __driver_attach => bus_for_each_dev => driver_attach => bus_add_driver => driver_register => __pci_register_driver => ext4_has_free_clusters => do_one_initcall => do_init_module => load_module => SYSC_init_module => SyS_init_module => entry_SYSCALL_64_fastpath This is happening on 3 boxes of mine running normal loads (servers, email, facebook, etc). Commit 0422e83d84ae2 says: Recursive locking for ww_mutexes was originally conceived as an exception. However, it is heavily used by the DRM atomic modesetting code. Currently, the recursive deadlock is checked after we have queued up for a busy-spin and as we never release the lock, we spin until kicked, whereupon the deadlock is discovered and reported. Should this be converted to a likely? -- Steve