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Subject: [mm PATCH] memremap: Fix reference count for pgmap in
 devm_memremap_pages
From:   Alexander Duyck <alexander.h.duyck@linux.intel.com>
To:     linux-mm@kvack.org, akpm@linux-foundation.org,
        dan.j.williams@intel.com
Cc:     pavel.tatashin@microsoft.com, mhocko@suse.com,
        dave.jiang@intel.com, linux-nvdimm@lists.01.org,
        linux-kernel@vger.kernel.org, dave.hansen@intel.com,
        jglisse@redhat.com, alexander.h.duyck@linux.intel.com,
        logang@deltatee.com, mingo@kernel.org,
        kirill.shutemov@linux.intel.com
Date:   Mon, 08 Oct 2018 16:34:33 -0700
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In the earlier patch "mm: defer ZONE_DEVICE page initialization to the
point where we init pgmap" I had overlooked the reference count that was
being held per page on the pgmap. As a result on running the ndctl test
"create.sh" we would call into devm_memremap_pages_release and encounter
the following percpu reference count error and hang:
  WARNING: CPU: 30 PID: 0 at lib/percpu-refcount.c:155
  percpu_ref_switch_to_atomic_rcu+0xf3/0x120

This patch addresses that by performing an update for all of the device
PFNs in a single call. In my testing this seems to resolve the issue while
still allowing us to retain the improvements seen in memory initialization.

Reported-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Alexander Duyck <alexander.h.duyck@linux.intel.com>
---
 kernel/memremap.c |    1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/memremap.c b/kernel/memremap.c
index 6ec81e0d7a33..9eced2cc9f94 100644
--- a/kernel/memremap.c
+++ b/kernel/memremap.c
@@ -218,6 +218,7 @@ void *devm_memremap_pages(struct device *dev, struct dev_pagemap *pgmap)
 	memmap_init_zone_device(&NODE_DATA(nid)->node_zones[ZONE_DEVICE],
 				align_start >> PAGE_SHIFT,
 				align_size >> PAGE_SHIFT, pgmap);
+	percpu_ref_get_many(pgmap->ref, pfn_end(pgmap) - pfn_first(pgmap));
 
 	devm_add_action(dev, devm_memremap_pages_release, pgmap);