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X-CSE-ConnectionGUID: tuP13doiQYiNpx9UJbRBcA== X-CSE-MsgGUID: lTWzXYN1SpiCGdnkvTCQKg== X-IronPort-AV: E=McAfee;i="6800,10657,11724"; a="74095842" X-IronPort-AV: E=Sophos;i="6.23,109,1770624000"; d="scan'208";a="74095842" Received: from fmviesa002.fm.intel.com ([10.60.135.142]) by orvoesa109.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 09 Mar 2026 13:21:32 -0700 X-CSE-ConnectionGUID: Z/bF/jxCS2eGzww6qcJBTw== X-CSE-MsgGUID: lr2mZe48QY6L/W3QG1kALw== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.23,109,1770624000"; d="scan'208";a="242882295" Received: from dwoodwor-mobl2.amr.corp.intel.com (HELO [10.125.109.205]) ([10.125.109.205]) by fmviesa002-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 09 Mar 2026 13:21:29 -0700 Message-ID: <68ed44be-9b21-47b7-a833-284aa471fb9b@intel.com> Date: Mon, 9 Mar 2026 13:21:28 -0700 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] cxl/hdm: fix a warning in devm_remove_action() To: Sungwoo Kim , Davidlohr Bueso , Jonathan Cameron , Alison Schofield , Vishal Verma , Ira Weiny , Dan Williams , Ben Widawsky Cc: Dave Tian , linux-cxl@vger.kernel.org, linux-kernel@vger.kernel.org References: <20260309000810.2632065-2-iam@sung-woo.kim> Content-Language: en-US From: Dave Jiang In-Reply-To: <20260309000810.2632065-2-iam@sung-woo.kim> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 3/8/26 5:08 PM, Sungwoo Kim wrote: > In the following race scenario, devm_remove_action() can be called > before devm_add_action(), triggering a warning because there is no > action to remove. > > To fix this, extend a critical section to embrace both > __cxl_dpa_reserve() and devm_add_action(). > > task 1: > cxl_dpa_alloc() > __cxl_dpa_reserve() ...(1) > devm_add_action() ...(4) > > task 2: > cxl_dpa_free() > guard() > if (!cxled->dpa_res) ...(2) pass, due to (1) > return 0; > devm_cxl_dpa_release() > devm_remove_action() ...(3) warning, no action is added yet > > Warning log: > > WARNING: ./include/linux/device/devres.h:160 at devm_remove_action include/linux/device/devres.h:160 [inline], CPU#0: syz.1.6464/25993 > WARNING: ./include/linux/device/devres.h:160 at devm_cxl_dpa_release drivers/cxl/core/hdm.c:290 [inline], CPU#0: syz.1.6464/25993 > WARNING: ./include/linux/device/devres.h:160 at cxl_dpa_free+0x2a4/0x320 drivers/cxl/core/hdm.c:572, CPU#0: syz.1.6464/25993 > Modules linked in: > CPU: 0 UID: 0 PID: 25993 Comm: syz.1.6464 Not tainted 6.19.0-g15a37b05f387 #10 PREEMPT(lazy) > Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.17.0-0-gb52ca86e094d-prebuilt.qemu.org 04/01/2014 > RIP: 0010:devm_remove_action include/linux/device/devres.h:160 [inline] > RIP: 0010:devm_cxl_dpa_release drivers/cxl/core/hdm.c:290 [inline] > RIP: 0010:cxl_dpa_free+0x2a4/0x320 drivers/cxl/core/hdm.c:572 > Code: 01 31 ff 41 89 c4 89 c6 e8 a9 91 1d fe 45 85 e4 0f 85 55 ff ff ff e8 4b 96 1d fe 90 0f 0b 90 e9 47 ff ff ff e8 3d 96 1d fe 90 <0f> 0b 90 e9 63 ff ff ff bb f0 ff ff ff e9 68 ff ff ff 48 c7 c7 f4 > RSP: 0018:ffff888129f77bb8 EFLAGS: 00010282 > RAX: 00000000000000f3 RBX: ffff888102f64000 RCX: ffffffff837301d3 > RDX: 0000000000080000 RSI: ffffc90001c5a000 RDI: 0000000000000005 > RBP: 00000000fffffffe R08: 0000000000000001 R09: ffff888123f98000 > R10: 00000000fffffffe R11: 0000000000000000 R12: 0000000000000001 > R13: ffff888102f64040 R14: dffffc0000000000 R15: ffff888102f64000 > FS: 00007fae0488d6c0(0000) GS:ffff88827086d000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 0000000000000000 CR3: 000000012f7d6003 CR4: 0000000000770ef0 > PKRU: 80000000 > Call Trace: > > dpa_size_store+0xfb/0x230 drivers/cxl/core/port.c:269 > dev_attr_store+0x58/0x80 drivers/base/core.c:2437 > sysfs_kf_write+0xf2/0x150 fs/sysfs/file.c:142 > kernfs_fop_write_iter+0x3d6/0x5d0 fs/kernfs/file.c:352 > new_sync_write fs/read_write.c:595 [inline] > vfs_write+0x68e/0x1050 fs/read_write.c:688 > ksys_write+0x12a/0x250 fs/read_write.c:740 > do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] > do_syscall_64+0xfc/0x670 arch/x86/entry/syscall_64.c:94 > entry_SYSCALL_64_after_hwframe+0x77/0x7f > RIP: 0033:0x7fae0399c669 > Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48 > RSP: 002b:00007fae0488d028 EFLAGS: 00000246 ORIG_RAX: 0000000000000001 > RAX: ffffffffffffffda RBX: 00007fae03c15fa0 RCX: 00007fae0399c669 > RDX: 000000000000000a RSI: 00002000000001c0 RDI: 0000000000000009 > RBP: 00007fae03a32c71 R08: 0000000000000000 R09: 0000000000000000 > R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 > R13: 00007fae03c16038 R14: 00007fae03c15fa0 R15: 00007ffe53519fb8 > > irq event stamp: 1021 > hardirqs last enabled at (1029): [] __up_console_sem+0x7b/0x90 kernel/printk/printk.c:347 > hardirqs last disabled at (1038): [] __up_console_sem+0x60/0x90 kernel/printk/printk.c:345 > softirqs last enabled at (1016): [] __do_softirq kernel/softirq.c:656 [inline] > softirqs last enabled at (1016): [] invoke_softirq kernel/softirq.c:496 [inline] > softirqs last enabled at (1016): [] __irq_exit_rcu+0xb3/0xe0 kernel/softirq.c:723 > softirqs last disabled at (1005): [] __do_softirq kernel/softirq.c:656 [inline] > softirqs last disabled at (1005): [] invoke_softirq kernel/softirq.c:496 [inline] > softirqs last disabled at (1005): [] __irq_exit_rcu+0xb3/0xe0 kernel/softirq.c:723 > > Fixes: cf880423b6a0 ("cxl/hdm: Add support for allocating DPA to an endpoint decoder") > Fixes: 9c57cde0dcbd ("cxl/hdm: Enumerate allocated DPA") > Signed-off-by: Sungwoo Kim Reviewed-by: Dave Jiang > --- > drivers/cxl/core/hdm.c | 34 +++++++++++++++++++++++++++++----- > 1 file changed, 29 insertions(+), 5 deletions(-) > > diff --git a/drivers/cxl/core/hdm.c b/drivers/cxl/core/hdm.c > index e3f0c39e68124..86239b1790a31 100644 > --- a/drivers/cxl/core/hdm.c > +++ b/drivers/cxl/core/hdm.c > @@ -509,13 +509,20 @@ int devm_cxl_dpa_reserve(struct cxl_endpoint_decoder *cxled, > struct cxl_port *port = cxled_to_port(cxled); > int rc; > > - scoped_guard(rwsem_write, &cxl_rwsem.dpa) > - rc = __cxl_dpa_reserve(cxled, base, len, skipped); > + guard(rwsem_write)(&cxl_rwsem.dpa); > + rc = __cxl_dpa_reserve(cxled, base, len, skipped); > > if (rc) > return rc; > > - return devm_add_action_or_reset(&port->dev, cxl_dpa_release, cxled); > + /* See comments in cxl_dpa_alloc()*/ > + rc = devm_add_action(&port->dev, cxl_dpa_release, cxled); > + if (rc) { > + __cxl_dpa_release(cxled); > + return rc; > + } > + > + return 0; > } > EXPORT_SYMBOL_NS_GPL(devm_cxl_dpa_reserve, "CXL"); > > @@ -613,7 +620,7 @@ static int __cxl_dpa_alloc(struct cxl_endpoint_decoder *cxled, u64 size) > struct resource *p, *last; > int part; > > - guard(rwsem_write)(&cxl_rwsem.dpa); > + lockdep_assert_held_write(&cxl_rwsem.dpa); > if (cxled->cxld.region) { > dev_dbg(dev, "decoder attached to %s\n", > dev_name(&cxled->cxld.region->dev)); > @@ -679,11 +686,28 @@ int cxl_dpa_alloc(struct cxl_endpoint_decoder *cxled, u64 size) > struct cxl_port *port = cxled_to_port(cxled); > int rc; > > + guard(rwsem_write)(&cxl_rwsem.dpa); > rc = __cxl_dpa_alloc(cxled, size); > if (rc) > return rc; > > - return devm_add_action_or_reset(&port->dev, cxl_dpa_release, cxled); > + /* > + * Add the devres action while still holding cxl_rwsem.dpa to prevent > + * a race with cxl_dpa_free(). Without this, a concurrent cxl_dpa_free() > + * can observe dpa_res set (by __cxl_dpa_reserve()) and attempt > + * devm_remove_action() before devm_add_action() has been called, > + * triggering a WARN_ON in devm_remove_action(). > + * Also, devm_add_action_or_reset() cannot be used here because > + * cxl_dpa_release() tries to hold the dpa lock that is already held, > + * causing a self deadlock. > + */ > + rc = devm_add_action(&port->dev, cxl_dpa_release, cxled); > + if (rc) { > + __cxl_dpa_release(cxled); > + return rc; > + } > + > + return 0; > } > > static void cxld_set_interleave(struct cxl_decoder *cxld, u32 *ctrl)