From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mgamail.intel.com (mgamail.intel.com [192.198.163.4]) (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 B40F64EB859 for ; Fri, 18 Sep 2026 15:26:31 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=192.198.163.4 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789745193; cv=none; b=CFhhVieKoUNQnRAJmfnXZF+xlVrXOGCHkaoBSMpnOei8Vejrlpza11uytntA/bBXH2gufsj9dE2mvvUo77AnqzRDb4xsIx+jOU3jM/HVUOPyLJqI6a8lYX2EEuWOjaP92PrpHNwFqNEY/wwh1P+tgJftORJgEbguJEmLNrAzCPY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789745193; c=relaxed/simple; bh=jYoQB8ncidccv5WHb4DvC8rbwdX7nH12lcxba9ugm1E=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=gKCBIseQoM/slqnjfWnTgytmjIfFyF7F822K/eae5fytCEsxgjtwzhKdE3O3gz0bbMEuEUGzVRVC+YSRCePyFYjLhzjbFmKSp8/MOd5sR2Ayywe19M8F1m3o8MXh66QslzDPjoXJ9MrnT0griI4YaqFCcepFTmmjtxVeYYT3bwc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=intel.com; spf=pass smtp.mailfrom=intel.com; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b=Apr6Gip0; arc=none smtp.client-ip=192.198.163.4 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=intel.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=intel.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b="Apr6Gip0" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1789745192; x=1821281192; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=jYoQB8ncidccv5WHb4DvC8rbwdX7nH12lcxba9ugm1E=; b=Apr6Gip0ot+SfNGTgLRJ+4Nrv0/CTaDzgvMDxtk0CgOi73oRAo4Qlo3i eocN6B0Ja+aq1WFrcn95ym+cD2rm3S+6VpncCGaRYxA4r3hybG32wh7te GVpzLu+1aek2YWE51As7LZ3c1aO8IDwxIFFC9GMMUTle5wzq1sBV+ADUz Bi126qZmcvdK/wa6hD4ufb0ggyO7EzeVpssjGvMmCxW5G1uISFq0QG2ZF u7pKHxrwqZOAi23oFJLH3EBHCmYY0lBNZMZpbXjtp5xiFOzpSKhi6dlY5 2FJYEcvwPjmQX4ION2YNqqw8+wTjFD+l94qXm9S+ckW71EpVc26DpmDoB g==; X-CSE-ConnectionGUID: eqO9uwE3TCi65+kClPa01w== X-CSE-MsgGUID: fe+OoGVvQCmtXA2Qft8GJA== X-IronPort-AV: E=McAfee;i="6800,10657,11909"; a="766371" X-IronPort-AV: E=Sophos;i="6.27,109,1787036400"; d="scan'208";a="766371" Received: from fmviesa011.fm.intel.com ([10.60.135.151]) by fmvoesa114.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 18 Sep 2026 08:26:31 -0700 X-CSE-ConnectionGUID: lnsFS2ODTP6Ro1TKS5eCkQ== X-CSE-MsgGUID: 8V4nfstaRpW3BkXp0yq/vQ== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.27,109,1787036400"; d="scan'208";a="2682184" Received: from sghuge-mobl2.amr.corp.intel.com (HELO [10.125.109.117]) ([10.125.109.117]) by smtpauth.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 18 Sep 2026 08:26:30 -0700 Message-ID: Date: Fri, 18 Sep 2026 08:26:28 -0700 Precedence: bulk X-Mailing-List: driver-core@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 0/2] cxl/memdev: Fix poison debugfs vs unbind deadlock To: Guixin Liu , Davidlohr Bueso , Jonathan Cameron , Alison Schofield , Vishal Verma , Dan Williams , Ira Weiny , Li Ming , Greg Kroah-Hartman , "Rafael J . Wysocki" , Danilo Krummrich , Shaikh Kamaluddin Cc: linux-cxl@vger.kernel.org, driver-core@lists.linux.dev References: <20260916025453.3532614-1-kanie@linux.alibaba.com> From: Dave Jiang Content-Language: en-US In-Reply-To: <20260916025453.3532614-1-kanie@linux.alibaba.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 9/15/26 7:54 PM, Guixin Liu wrote: > Writing a memdev poison debugfs file while cxl_mem is being unbound > deadlocks. Patch 2 fixes it by not waiting for the device lock in those > handlers. Patch 1 adds the trylock guard it uses. > > Patch 2 does not build without patch 1, so the two need to travel > together. > > Testing: > > Reproduced on a QEMU CXL topology whose type3 devices advertise poison > inject support: > > while :; do echo 0 > /sys/kernel/debug/cxl/mem0/inject_poison; done & > while :; do > echo mem0 > /sys/bus/cxl/drivers/cxl_mem/unbind > echo mem0 > /sys/bus/cxl/drivers/cxl_mem/bind > done > > Without the fix the unbind wedges within seconds. The three tasks > involved, from /proc//stack: > > writer, state S, holds the debugfs reference and waits for the lock > cxl_debugfs_poison_inject+0x25/0xa0 [cxl_mem] > debugfs_attr_write+0x61/0xb0 > full_proxy_write+0xfc/0x1c0 > vfs_write+0x1d4/0xe60 > > unbind, state D, holds the lock and waits for the reference to drain > remove_one+0x27f/0x3d0 > debugfs_remove+0x44/0x60 > release_nodes+0xfa/0x2c0 > devres_release_all+0x113/0x1a0 > device_unbind_cleanup+0x76/0x260 > device_release_driver_internal+0x3eb/0x540 > unbind_store+0xde/0x100 > > cxl_port workqueue, state D, blocked on the same lock > device_release_driver_internal+0x96/0x540 > detach_memdev+0x79/0xb0 [cxl_core] > process_one_work+0x6b0/0xfb0 > > The writer is in interruptible sleep and can be killed; the unbind > cannot, and because cxl_bus_wq is an ordered workqueue the wedged > detach_memdev() blocks every other CXL bus work item behind it. > > The same deadlock shows up with a pciehp hot-remove racing the writer > loop: the pciehp thread hits the same debugfs_remove() drain holding > the memdev lock, and the hot-remove wedges the same way. With both > patches applied the hot-remove flow completes normally. > > With both patches applied, 46 unbind/bind cycles against the same writer > loop all completed, no task was left in D state, and the writer collected > 10920 EBUSY returns from the contended trylock. Note that lockdep stays > quiet either way: one leg of the cycle is the debugfs active_users > completion rather than a lock it tracks. > > v3 -> v4: > - reword the patch 2 commit message per Alison: enumerate the teardown > paths that race a poison write into an unbind, and state that mixing > poison writes with cxl_mem teardown is not a supported use of this > debug ABI, though the fix keeps the cost of doing so to a failed write > - add the pciehp hot-remove reproduction, reported during v3 review, > to the patch 2 commit message > - collect Jonathan's Reviewed-by on both patches (no code change) > > v1 -> v2: > - add the device_trylock() guard and use ACQUIRE(device_try, ...) instead > of open-coding device_trylock()/device_unlock(), keeping the style the > Fixes: commit established (Shaikh Kamaluddin) > - cut the changelog down to the failing condition, the consequence and > the fix; the call graph and the reproducer live here instead > - say how the issue was found and how it was tested > > v2 -> v3: > - rebase onto v7.3-rc2 (master), per Dave's request to send the series > against Linus's tags rather than cxl/next > > v1: > https://lore.kernel.org/linux-cxl/20260826125248.4003792-1-kanie@linux.alibaba.com/ > > v2: > https://lore.kernel.org/linux-cxl/20260831124809.889829-1-kanie@linux.alibaba.com/ > > v3: > https://lore.kernel.org/linux-cxl/20260910094017.4032170-1-kanie@linux.alibaba.com/ > > Guixin Liu (2): > driver core: Add conditional guard support for device_trylock() > cxl/memdev: Fix deadlock between poison debugfs and cxl_mem unbind > > drivers/cxl/mem.c | 14 ++++++++++---- > include/linux/device.h | 1 + > 2 files changed, 11 insertions(+), 4 deletions(-) > For the series Reviewed-by: Dave Jiang Greg, I can take the patches through the CXL tree if you ack the first patch. Thanks!