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([128.210.0.165]) by smtp.googlemail.com with ESMTPSA id 00721157ae682-79cba172828sm34618347b3.35.2026.03.30.06.04.51 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 30 Mar 2026 06:04:52 -0700 (PDT) From: Sungwoo Kim To: Davidlohr Bueso , Jonathan Cameron , Dave Jiang , Alison Schofield , Vishal Verma , Ira Weiny , Dan Williams , Ben Widawsky Cc: Dave Tian , Sungwoo Kim , Jonathan Cameron , linux-cxl@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH v2] cxl/hdm: fix a warning in devm_remove_action() Date: Mon, 30 Mar 2026 09:01:57 -0400 Message-ID: <20260330130156.2212694-3-iam@sung-woo.kim> X-Mailer: git-send-email 2.47.3 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" 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, __cxl_dpa_reserve() performs devm_add_action(). This extends the critical section that embraces cxled->dpa_res =3D res and devm_add_action(), so cxl_dpa_free() cannot observe dpa_res without the devres action. task 1: cxl_dpa_alloc() __cxl_dpa_alloc() guard(&cxl_rwsem.dpa) cxled->dpa_res =3D res; ...(1) devm_add_action() ...(4) task 2: cxl_dpa_free() guard(&cxl_rwsem.dpa) 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 Splat: 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 driver= s/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 dr= ivers/cxl/core/hdm.c:572, CPU#0: syz.1.6464/25993 Fixes: cf880423b6a0 ("cxl/hdm: Add support for allocating DPA to an endpoin= t decoder") Fixes: 9c57cde0dcbd ("cxl/hdm: Enumerate allocated DPA") Signed-off-by: Sungwoo Kim --- V1: https://lore.kernel.org/linux-cxl/20260309000810.2632065-2-iam@sung-woo= .kim/ V1->V2: - Let __cxl_dpa_reserve() handle devm_remove_action() to reduce duplicated patches. (Thanks to Dan for the suggestion) - Make the comment concise (Reflect Dan and Alison's comments) - Make a warning log in a commit message concise drivers/cxl/core/hdm.c | 33 +++++++++++++-------------------- 1 file changed, 13 insertions(+), 20 deletions(-) diff --git a/drivers/cxl/core/hdm.c b/drivers/cxl/core/hdm.c index cb5d5a047a9d..63bd0d5f31df 100644 --- a/drivers/cxl/core/hdm.c +++ b/drivers/cxl/core/hdm.c @@ -408,7 +408,13 @@ static int __cxl_dpa_reserve(struct cxl_endpoint_decod= er *cxled, =20 port->hdm_end++; get_device(&cxled->cxld.dev); - return 0; + + /* + * Perform devres registration while holding cxl_rwsem.dpa so + * cxl_dpa_free() cannot observe dpa_res without a matching devres + * action. + */ + return devm_add_action_or_reset(&port->dev, cxl_dpa_release, cxled); } =20 static int add_dpa_res(struct device *dev, struct resource *parent, @@ -499,16 +505,8 @@ int devm_cxl_dpa_reserve(struct cxl_endpoint_decoder *= cxled, resource_size_t base, resource_size_t len, resource_size_t skipped) { - struct cxl_port *port =3D cxled_to_port(cxled); - int rc; - - scoped_guard(rwsem_write, &cxl_rwsem.dpa) - rc =3D __cxl_dpa_reserve(cxled, base, len, skipped); - - if (rc) - return rc; - - return devm_add_action_or_reset(&port->dev, cxl_dpa_release, cxled); + guard(rwsem_write)(&cxl_rwsem.dpa); + return __cxl_dpa_reserve(cxled, base, len, skipped); } EXPORT_SYMBOL_NS_GPL(devm_cxl_dpa_reserve, "CXL"); =20 @@ -606,7 +604,8 @@ static int __cxl_dpa_alloc(struct cxl_endpoint_decoder = *cxled, u64 size) struct resource *p, *last; int part; =20 - 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)); @@ -669,14 +668,8 @@ static int __cxl_dpa_alloc(struct cxl_endpoint_decoder= *cxled, u64 size) =20 int cxl_dpa_alloc(struct cxl_endpoint_decoder *cxled, u64 size) { - struct cxl_port *port =3D cxled_to_port(cxled); - int rc; - - rc =3D __cxl_dpa_alloc(cxled, size); - if (rc) - return rc; - - return devm_add_action_or_reset(&port->dev, cxl_dpa_release, cxled); + guard(rwsem_write)(&cxl_rwsem.dpa); + return __cxl_dpa_alloc(cxled, size); } =20 static void cxld_set_interleave(struct cxl_decoder *cxld, u32 *ctrl) --=20 2.47.3