From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D7A65C433F5 for ; Fri, 1 Oct 2021 09:14:59 +0000 (UTC) Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 9FA9361131 for ; Fri, 1 Oct 2021 09:14:59 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 9FA9361131 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=intel.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=lists.freedesktop.org Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 2346A6ED7D; Fri, 1 Oct 2021 09:14:53 +0000 (UTC) Received: from mga11.intel.com (mga11.intel.com [192.55.52.93]) by gabe.freedesktop.org (Postfix) with ESMTPS id 6CEE76ED7C; Fri, 1 Oct 2021 09:14:51 +0000 (UTC) X-IronPort-AV: E=McAfee;i="6200,9189,10123"; a="222178976" X-IronPort-AV: E=Sophos;i="5.85,337,1624345200"; d="scan'208";a="222178976" Received: from fmsmga001.fm.intel.com ([10.253.24.23]) by fmsmga102.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 01 Oct 2021 02:14:51 -0700 X-IronPort-AV: E=Sophos;i="5.85,337,1624345200"; d="scan'208";a="618930263" Received: from kdoertel-mobl.ger.corp.intel.com (HELO localhost) ([10.251.222.34]) by fmsmga001-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 01 Oct 2021 02:14:48 -0700 From: Jani Nikula To: Jani Nikula , dri-devel@lists.freedesktop.org Cc: intel-gfx@lists.freedesktop.org, Daniel Vetter , Dave Airlie , Daniel Vetter Date: Fri, 1 Oct 2021 12:14:44 +0300 Message-Id: <20211001091444.8177-1-jani.nikula@intel.com> X-Mailer: git-send-email 2.30.2 In-Reply-To: <20210928223241.22149-1-jani.nikula@intel.com> References: <20210928223241.22149-1-jani.nikula@intel.com> MIME-Version: 1.0 Organization: Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo Content-Transfer-Encoding: 8bit Subject: [Intel-gfx] [PATCH v2] drm/locking: add backtrace for locking contended locks without backoff X-BeenThere: intel-gfx@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Intel graphics driver community testing & development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: intel-gfx-bounces@lists.freedesktop.org Sender: "Intel-gfx" If drm_modeset_lock() returns -EDEADLK, the caller is supposed to drop all currently held locks using drm_modeset_backoff(). Failing to do so will result in warnings and backtraces on the paths trying to lock a contended lock. Add support for optionally printing the backtrace on the path that hit the deadlock and didn't gracefully handle the situation. For example, the patch [1] inadvertently dropped the return value check and error return on replacing calc_watermark_data() with intel_compute_global_watermarks(). The backtraces on the subsequent locking paths hitting WARN_ON(ctx->contended) were unhelpful, but adding the backtrace to the deadlock path produced this helpful printout: <7> [98.002465] drm_modeset_lock attempting to lock a contended lock without backoff: drm_modeset_lock+0x107/0x130 drm_atomic_get_plane_state+0x76/0x150 skl_compute_wm+0x251d/0x2b20 [i915] intel_atomic_check+0x1942/0x29e0 [i915] drm_atomic_check_only+0x554/0x910 drm_atomic_nonblocking_commit+0xe/0x50 drm_mode_atomic_ioctl+0x8c2/0xab0 drm_ioctl_kernel+0xac/0x140 Add new CONFIG_DRM_DEBUG_MODESET_LOCK to enable modeset lock debugging with stack depot and trace. [1] https://lore.kernel.org/r/20210924114741.15940-4-jani.nikula@intel.com v2: - default y if DEBUG_WW_MUTEX_SLOWPATH (Daniel) - depends on DEBUG_KERNEL Cc: Daniel Vetter Cc: Dave Airlie Reviewed-by: Daniel Vetter Signed-off-by: Jani Nikula --- drivers/gpu/drm/Kconfig | 15 +++++++++ drivers/gpu/drm/drm_modeset_lock.c | 49 ++++++++++++++++++++++++++++-- include/drm/drm_modeset_lock.h | 8 +++++ 3 files changed, 70 insertions(+), 2 deletions(-) diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig index 2a926d0de423..a4c020a9a0eb 100644 --- a/drivers/gpu/drm/Kconfig +++ b/drivers/gpu/drm/Kconfig @@ -100,6 +100,21 @@ config DRM_DEBUG_DP_MST_TOPOLOGY_REFS This has the potential to use a lot of memory and print some very large kernel messages. If in doubt, say "N". +config DRM_DEBUG_MODESET_LOCK + bool "Enable backtrace history for lock contention" + depends on STACKTRACE_SUPPORT + depends on DEBUG_KERNEL + depends on EXPERT + select STACKDEPOT + default y if DEBUG_WW_MUTEX_SLOWPATH + help + Enable debug tracing of failures to gracefully handle drm modeset lock + contention. A history of each drm modeset lock path hitting -EDEADLK + will be saved until gracefully handled, and the backtrace will be + printed when attempting to lock a contended lock. + + If in doubt, say "N". + config DRM_FBDEV_EMULATION bool "Enable legacy fbdev support for your modesetting driver" depends on DRM diff --git a/drivers/gpu/drm/drm_modeset_lock.c b/drivers/gpu/drm/drm_modeset_lock.c index bf8a6e823a15..4d32b61fa1fd 100644 --- a/drivers/gpu/drm/drm_modeset_lock.c +++ b/drivers/gpu/drm/drm_modeset_lock.c @@ -25,6 +25,7 @@ #include #include #include +#include /** * DOC: kms locking @@ -77,6 +78,45 @@ static DEFINE_WW_CLASS(crtc_ww_class); +#if IS_ENABLED(CONFIG_DRM_DEBUG_MODESET_LOCK) +static noinline depot_stack_handle_t __stack_depot_save(void) +{ + unsigned long entries[8]; + unsigned int n; + + n = stack_trace_save(entries, ARRAY_SIZE(entries), 1); + + return stack_depot_save(entries, n, GFP_NOWAIT | __GFP_NOWARN); +} + +static void __stack_depot_print(depot_stack_handle_t stack_depot) +{ + struct drm_printer p = drm_debug_printer("drm_modeset_lock"); + unsigned long *entries; + unsigned int nr_entries; + char *buf; + + buf = kmalloc(PAGE_SIZE, GFP_NOWAIT | __GFP_NOWARN); + if (!buf) + return; + + nr_entries = stack_depot_fetch(stack_depot, &entries); + stack_trace_snprint(buf, PAGE_SIZE, entries, nr_entries, 2); + + drm_printf(&p, "attempting to lock a contended lock without backoff:\n%s", buf); + + kfree(buf); +} +#else /* CONFIG_DRM_DEBUG_MODESET_LOCK */ +static depot_stack_handle_t __stack_depot_save(void) +{ + return 0; +} +static void __stack_depot_print(depot_stack_handle_t stack_depot) +{ +} +#endif /* CONFIG_DRM_DEBUG_MODESET_LOCK */ + /** * drm_modeset_lock_all - take all modeset locks * @dev: DRM device @@ -225,7 +265,9 @@ EXPORT_SYMBOL(drm_modeset_acquire_fini); */ void drm_modeset_drop_locks(struct drm_modeset_acquire_ctx *ctx) { - WARN_ON(ctx->contended); + if (WARN_ON(ctx->contended)) + __stack_depot_print(ctx->stack_depot); + while (!list_empty(&ctx->locked)) { struct drm_modeset_lock *lock; @@ -243,7 +285,8 @@ static inline int modeset_lock(struct drm_modeset_lock *lock, { int ret; - WARN_ON(ctx->contended); + if (WARN_ON(ctx->contended)) + __stack_depot_print(ctx->stack_depot); if (ctx->trylock_only) { lockdep_assert_held(&ctx->ww_ctx); @@ -274,6 +317,7 @@ static inline int modeset_lock(struct drm_modeset_lock *lock, ret = 0; } else if (ret == -EDEADLK) { ctx->contended = lock; + ctx->stack_depot = __stack_depot_save(); } return ret; @@ -296,6 +340,7 @@ int drm_modeset_backoff(struct drm_modeset_acquire_ctx *ctx) struct drm_modeset_lock *contended = ctx->contended; ctx->contended = NULL; + ctx->stack_depot = 0; if (WARN_ON(!contended)) return 0; diff --git a/include/drm/drm_modeset_lock.h b/include/drm/drm_modeset_lock.h index aafd07388eb7..b84693fbd2b5 100644 --- a/include/drm/drm_modeset_lock.h +++ b/include/drm/drm_modeset_lock.h @@ -24,6 +24,8 @@ #ifndef DRM_MODESET_LOCK_H_ #define DRM_MODESET_LOCK_H_ +#include /* stackdepot.h is not self-contained */ +#include #include struct drm_modeset_lock; @@ -51,6 +53,12 @@ struct drm_modeset_acquire_ctx { */ struct drm_modeset_lock *contended; + /* + * Stack depot for debugging when a contended lock was not backed off + * from. + */ + depot_stack_handle_t stack_depot; + /* * list of held locks (drm_modeset_lock) */ -- 2.30.2