From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 8586846EC82; Tue, 21 Jul 2026 19:23:54 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784661835; cv=none; b=A4KF0JJlex2QrLFd2ltqvzBTi76VRXSvt6JHcBIf3eEBPS0DZEr93Oqv+HHXnpuWf2o4fIrfTCUuap+orr6sNawdH3w0Nb9fhVR4UrAsMEhx4YbhaSlauyS6f6T/i5qZd4imYX6/rrbSSdcsdRsiNHWiKBASc5Ccr/s/ZEmDFZc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784661835; c=relaxed/simple; bh=1ZRznMGIUgWaRB3Ictci+WZ6MoFmoT98/J6Qk9dgNvo=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=jtos0R4H/5rwUOOXE8ilElvR2OLidWV/HEhhG0tNrUiV7YacPMrdmSwZOJQDek/wFxS3n9seOgCk4Av8whm3YQFYcyGoahimRBX0gq8z476Lv16RAuTBgllR0d7q3/ye136fXG1LMlwUf9qOlzpCvSDaLGIt739cEIr/p0NklmE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=qegFz6Sf; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="qegFz6Sf" Received: by smtp.kernel.org (Postfix) with ESMTPSA id EB2E81F000E9; Tue, 21 Jul 2026 19:23:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1784661834; bh=f7l+qxz2ED5iz31gREZB4MJvhi+LYuAcyuOt1X5Ev30=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=qegFz6Sf9rK6lS0OPVIAQZ4tNT9w683so2FvBTSnSIy1R3670pk1imjqLu5/Bw2HE 9ifsIOHLz6QWXqwBx2ToyYBSRRJKjkFkn3X/MWCjUHRlVXPAnEjMBv1ydgRvgLQUsp Lgkz7X3YfR38B/EpzCGyUXZKesE1yt9J1ZG1q2HI= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Aboorva Devarajan , Vishal Verma , Dave Jiang , Alison Schofield , Sasha Levin Subject: [PATCH 6.12 0215/1276] nvdimm/btt: Handle preemption in BTT lane acquisition Date: Tue, 21 Jul 2026 17:10:58 +0200 Message-ID: <20260721152450.896991759@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260721152446.065700225@linuxfoundation.org> References: <20260721152446.065700225@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.12-stable review patch. If anyone has any objections, please let me know. ------------------ From: Alison Schofield [ Upstream commit 8d4b989d9c9afe5f185aa5853b666fc4617afe9e ] BTT lanes serialize access to per-lane metadata and workspace state during BTT I/O. The btt-check unit test reports data mismatches during BTT writes due to a race in lane acquisition that can lead to silent data corruption. The existing lane model uses a spinlock together with a per-CPU recursion count. That recursion model stopped being valid after BTT lanes became preemptible: another task can run on the same CPU, observe a non-zero recursion count, bypass locking, and use the same lane concurrently. BTT lanes are also held across arena_write_bytes() calls. That path reaches nsio_rw_bytes(), which flushes writes with nvdimm_flush(). Some provider flush callbacks can sleep, making a spinlock the wrong primitive for the lane lifetime. Replace the spinlock-based recursion model with a dynamically allocated per-lane mutex array and take the lane lock unconditionally. Add might_sleep() to catch any future atomic-context caller. Found with the ndctl unit test btt-check.sh. Fixes: 36c75ce3bd29 ("nd_btt: Make BTT lanes preemptible") Assisted-by: Claude-Sonnet:4.5 Tested-by: Aboorva Devarajan Reviewed-by: Aboorva Devarajan Reviewed-by: Vishal Verma Reviewed-by: Dave Jiang Link: https://patch.msgid.link/20260528021625.618462-1-alison.schofield@intel.com Signed-off-by: Alison Schofield Signed-off-by: Sasha Levin --- Documentation/driver-api/nvdimm/btt.rst | 5 +- drivers/nvdimm/nd.h | 11 ++--- drivers/nvdimm/region_devs.c | 66 +++++++++---------------- 3 files changed, 29 insertions(+), 53 deletions(-) diff --git a/Documentation/driver-api/nvdimm/btt.rst b/Documentation/driver-api/nvdimm/btt.rst index 107395c042ae07..cb1afe9dc3cbb9 100644 --- a/Documentation/driver-api/nvdimm/btt.rst +++ b/Documentation/driver-api/nvdimm/btt.rst @@ -161,9 +161,8 @@ process:: nlanes = min(nfree, num_cpus) A lane number is obtained at the start of any IO, and is used for indexing into -all the on-disk and in-memory data structures for the duration of the IO. If -there are more CPUs than the max number of available lanes, than lanes are -protected by spinlocks. +all the on-disk and in-memory data structures for the duration of the IO. Lanes +are protected by mutexes. d. In-memory data structure: Read Tracking Table (RTT) diff --git a/drivers/nvdimm/nd.h b/drivers/nvdimm/nd.h index 5ca06e9a2d2925..28ea8b94bae0bc 100644 --- a/drivers/nvdimm/nd.h +++ b/drivers/nvdimm/nd.h @@ -365,11 +365,6 @@ unsigned sizeof_namespace_label(struct nvdimm_drvdata *ndd); for (res = (ndd)->dpa.child, next = res ? res->sibling : NULL; \ res; res = next, next = next ? next->sibling : NULL) -struct nd_percpu_lane { - int count; - spinlock_t lock; -}; - enum nd_label_flags { ND_LABEL_REAP, }; @@ -400,6 +395,10 @@ struct nd_mapping { struct nvdimm_drvdata *ndd; }; +struct nd_lane { + struct mutex lock; /* serialize lane access */ +} ____cacheline_aligned_in_smp; + struct nd_region { struct device dev; struct ida ns_ida; @@ -420,7 +419,7 @@ struct nd_region { struct kernfs_node *bb_state; struct badblocks bb; struct nd_interleave_set *nd_set; - struct nd_percpu_lane __percpu *lane; + struct nd_lane *lane; int (*flush)(struct nd_region *nd_region, struct bio *bio); struct nd_mapping mapping[] __counted_by(ndr_mappings); }; diff --git a/drivers/nvdimm/region_devs.c b/drivers/nvdimm/region_devs.c index 9e4f7ff024a000..849c131f39c757 100644 --- a/drivers/nvdimm/region_devs.c +++ b/drivers/nvdimm/region_devs.c @@ -179,7 +179,9 @@ static void nd_region_release(struct device *dev) put_device(&nvdimm->dev); } - free_percpu(nd_region->lane); + for (i = 0; i < nd_region->num_lanes; i++) + mutex_destroy(&nd_region->lane[i].lock); + kfree(nd_region->lane); if (!test_bit(ND_REGION_CXL, &nd_region->flags)) memregion_free(nd_region->id); kfree(nd_region); @@ -922,52 +924,30 @@ void nd_region_advance_seeds(struct nd_region *nd_region, struct device *dev) * nd_region_acquire_lane - allocate and lock a lane * @nd_region: region id and number of lanes possible * - * A lane correlates to a BLK-data-window and/or a log slot in the BTT. - * We optimize for the common case where there are 256 lanes, one - * per-cpu. For larger systems we need to lock to share lanes. For now - * this implementation assumes the cost of maintaining an allocator for - * free lanes is on the order of the lock hold time, so it implements a - * static lane = cpu % num_lanes mapping. + * A lane correlates to a log slot in the BTT. Lanes are shared across + * CPUs using a static lane = cpu % num_lanes mapping, with a per-lane + * mutex to serialize access. * - * In the case of a BTT instance on top of a BLK namespace a lane may be - * acquired recursively. We lock on the first instance. - * - * In the case of a BTT instance on top of PMEM, we only acquire a lane - * for the BTT metadata updates. + * Callers must be in sleepable context. The only in-tree caller is + * BTT's ->submit_bio handler (btt_read_pg / btt_write_pg). */ unsigned int nd_region_acquire_lane(struct nd_region *nd_region) + __acquires(&nd_region->lane[lane].lock) { - unsigned int cpu, lane; - - migrate_disable(); - cpu = smp_processor_id(); - if (nd_region->num_lanes < nr_cpu_ids) { - struct nd_percpu_lane *ndl_lock, *ndl_count; + unsigned int lane; - lane = cpu % nd_region->num_lanes; - ndl_count = per_cpu_ptr(nd_region->lane, cpu); - ndl_lock = per_cpu_ptr(nd_region->lane, lane); - if (ndl_count->count++ == 0) - spin_lock(&ndl_lock->lock); - } else - lane = cpu; + might_sleep(); + lane = raw_smp_processor_id() % nd_region->num_lanes; + mutex_lock(&nd_region->lane[lane].lock); return lane; } EXPORT_SYMBOL(nd_region_acquire_lane); void nd_region_release_lane(struct nd_region *nd_region, unsigned int lane) + __releases(&nd_region->lane[lane].lock) { - if (nd_region->num_lanes < nr_cpu_ids) { - unsigned int cpu = smp_processor_id(); - struct nd_percpu_lane *ndl_lock, *ndl_count; - - ndl_count = per_cpu_ptr(nd_region->lane, cpu); - ndl_lock = per_cpu_ptr(nd_region->lane, lane); - if (--ndl_count->count == 0) - spin_unlock(&ndl_lock->lock); - } - migrate_enable(); + mutex_unlock(&nd_region->lane[lane].lock); } EXPORT_SYMBOL(nd_region_release_lane); @@ -1038,17 +1018,16 @@ static struct nd_region *nd_region_create(struct nvdimm_bus *nvdimm_bus, goto err_id; } - nd_region->lane = alloc_percpu(struct nd_percpu_lane); + nd_region->num_lanes = ndr_desc->num_lanes; + if (!nd_region->num_lanes) + goto err_percpu; + nd_region->lane = kcalloc(nd_region->num_lanes, + sizeof(*nd_region->lane), GFP_KERNEL); if (!nd_region->lane) goto err_percpu; - for (i = 0; i < nr_cpu_ids; i++) { - struct nd_percpu_lane *ndl; - - ndl = per_cpu_ptr(nd_region->lane, i); - spin_lock_init(&ndl->lock); - ndl->count = 0; - } + for (i = 0; i < nd_region->num_lanes; i++) + mutex_init(&nd_region->lane[i].lock); for (i = 0; i < ndr_desc->num_mappings; i++) { struct nd_mapping_desc *mapping = &ndr_desc->mapping[i]; @@ -1065,7 +1044,6 @@ static struct nd_region *nd_region_create(struct nvdimm_bus *nvdimm_bus, } nd_region->provider_data = ndr_desc->provider_data; nd_region->nd_set = ndr_desc->nd_set; - nd_region->num_lanes = ndr_desc->num_lanes; nd_region->flags = ndr_desc->flags; nd_region->ro = ro; nd_region->numa_node = ndr_desc->numa_node; -- 2.53.0