From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mga05.intel.com (mga05.intel.com [192.55.52.43]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D956E1FC0 for ; Thu, 21 Apr 2022 15:37:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1650555457; x=1682091457; h=subject:from:to:cc:date:message-id:in-reply-to: references:mime-version:content-transfer-encoding; bh=x3xS6cEt6lHXiNb+A1o9kWq7JklXoM+r+tP2gN5rJV4=; b=FvZ3IPImbhBy9ySPXiIu9SP/UeHnWiXU+229yo/2CgC+zyBxHq7NmT7S B/P7rxnp8AgmcRqJg8qTqZe3EEmr2R2p9MLDlzePSZBBud8sRA8Aesw5L z+IpU5PBXkorlzHi0P2Jho/+WEi+8rZRbjJC/fdLvubKe6e3PCTLsHK0m eb4QcW5rGv19StuSutWmadWekx935ZmmKjeDHuL+KNcaD0BPTE9T3LHIe glJxBLkuQ+/pS9RZ6wMc04ZASP5kcnjlHYml13rjTpxQQCjbQcy8LDaJZ 6i7iDxdIMKGi/pQPwCAC7PmZhUgI7h3Ot1VJ/+FLxiPiHmuDqPotFaYUZ Q==; X-IronPort-AV: E=McAfee;i="6400,9594,10324"; a="350833505" X-IronPort-AV: E=Sophos;i="5.90,279,1643702400"; d="scan'208";a="350833505" Received: from orsmga006.jf.intel.com ([10.7.209.51]) by fmsmga105.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 21 Apr 2022 08:33:51 -0700 X-IronPort-AV: E=Sophos;i="5.90,279,1643702400"; d="scan'208";a="530353769" Received: from dwillia2-desk3.jf.intel.com (HELO dwillia2-desk3.amr.corp.intel.com) ([10.54.39.25]) by orsmga006-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 21 Apr 2022 08:33:51 -0700 Subject: [PATCH v3 8/8] nvdimm: Fix firmware activation deadlock scenarios From: Dan Williams To: linux-cxl@vger.kernel.org Cc: peterz@infradead.org, vishal.l.verma@intel.com, alison.schofield@intel.com, nvdimm@lists.linux.dev, linux-kernel@vger.kernel.org Date: Thu, 21 Apr 2022 08:33:51 -0700 Message-ID: <165055523099.3745911.9091010720291846249.stgit@dwillia2-desk3.amr.corp.intel.com> In-Reply-To: <165055518776.3745911.9346998911322224736.stgit@dwillia2-desk3.amr.corp.intel.com> References: <165055518776.3745911.9346998911322224736.stgit@dwillia2-desk3.amr.corp.intel.com> User-Agent: StGit/0.18-3-g996c Precedence: bulk X-Mailing-List: nvdimm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Lockdep reports the following deadlock scenarios for CXL root device power-management, device_prepare(), operations, and device_shutdown() operations for 'nd_region' devices: --- Chain exists of: &nvdimm_region_key --> &nvdimm_bus->reconfig_mutex --> system_transition_mutex Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(system_transition_mutex); lock(&nvdimm_bus->reconfig_mutex); lock(system_transition_mutex); lock(&nvdimm_region_key); -- Chain exists of: &cxl_nvdimm_bridge_key --> acpi_scan_lock --> &cxl_root_key Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(&cxl_root_key); lock(acpi_scan_lock); lock(&cxl_root_key); lock(&cxl_nvdimm_bridge_key); --- These stem from holding nvdimm_bus_lock() over hibernate_quiet_exec() which walks the entire system device topology taking device_lock() along the way. The nvdimm_bus_lock() is protecting against unregistration, multiple simultaneous ops callers, and preventing activate_show() from racing activate_store(). For the first 2, the lock is redundant. Unregistration already flushes all ops users, and sysfs already prevents multiple threads to be active in an ops handler at the same time. For the last userspace should already be waiting for its last activate_store() to complete, and does not need activate_show() to flush the write side, so this lock usage can be deleted in these attributes. Fixes: 48001ea50d17 ("PM, libnvdimm: Add runtime firmware activation support") Signed-off-by: Dan Williams --- drivers/nvdimm/core.c | 4 ---- 1 file changed, 4 deletions(-) diff --git a/drivers/nvdimm/core.c b/drivers/nvdimm/core.c index 144926b7451c..7c7f4a43fd4f 100644 --- a/drivers/nvdimm/core.c +++ b/drivers/nvdimm/core.c @@ -395,10 +395,8 @@ static ssize_t activate_show(struct device *dev, if (!nd_desc->fw_ops) return -EOPNOTSUPP; - nvdimm_bus_lock(dev); cap = nd_desc->fw_ops->capability(nd_desc); state = nd_desc->fw_ops->activate_state(nd_desc); - nvdimm_bus_unlock(dev); if (cap < NVDIMM_FWA_CAP_QUIESCE) return -EOPNOTSUPP; @@ -443,7 +441,6 @@ static ssize_t activate_store(struct device *dev, else return -EINVAL; - nvdimm_bus_lock(dev); state = nd_desc->fw_ops->activate_state(nd_desc); switch (state) { @@ -461,7 +458,6 @@ static ssize_t activate_store(struct device *dev, default: rc = -ENXIO; } - nvdimm_bus_unlock(dev); if (rc == 0) rc = len;