[PATCH v2 1/2] mm, devm_memremap_pages: hold device_hotplug lock over mem_hotplug_{begin, done}

[Dan Williams <dan.j.williams@intel.com>]

The mem_hotplug_{begin,done} lock coordinates with
{get,put}_online_mems() to hold off "readers" of the current state of
memory from new hotplug actions. mem_hotplug_begin() expects exclusive
access, via the device_hotplug lock, to set mem_hotplug.active_writer.
Calling mem_hotplug_begin() without locking device_hotplug can lead to
corrupting mem_hotplug.refcount and missed wakeups / soft lockups.

Cc: <stable@vger.kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Toshi Kani <toshi.kani@hpe.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Logan Gunthorpe <logang@deltatee.com>
Fixes: f931ab479dd2 ("mm: fix devm_memremap_pages crash, use mem_hotplug_{begin, done}")
Reported-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
 kernel/memremap.c |    6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/kernel/memremap.c b/kernel/memremap.c
index 9ecedc28b928..06123234f118 100644
--- a/kernel/memremap.c
+++ b/kernel/memremap.c
@@ -246,9 +246,13 @@ static void devm_memremap_pages_release(struct device *dev, void *data)
 	/* pages are dead and unused, undo the arch mapping */
 	align_start = res->start & ~(SECTION_SIZE - 1);
 	align_size = ALIGN(resource_size(res), SECTION_SIZE);
+
+	lock_device_hotplug();
 	mem_hotplug_begin();
 	arch_remove_memory(align_start, align_size);
 	mem_hotplug_done();
+	unlock_device_hotplug();
+
 	untrack_pfn(NULL, PHYS_PFN(align_start), align_size);
 	pgmap_radix_release(res);
 	dev_WARN_ONCE(dev, pgmap->altmap && pgmap->altmap->alloc,
@@ -360,9 +364,11 @@ void *devm_memremap_pages(struct device *dev, struct resource *res,
 	if (error)
 		goto err_pfn_remap;
 
+	lock_device_hotplug();
 	mem_hotplug_begin();
 	error = arch_add_memory(nid, align_start, align_size, true);
 	mem_hotplug_done();
+	unlock_device_hotplug();
 	if (error)
 		goto err_add_memory;
 

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