mm, devm_memremap_pages: fix shutdown handling

The last step before devm_memremap_pages() returns success is to allocate
a release action, devm_memremap_pages_release(), to tear the entire setup
down.  However, the result from devm_add_action() is not checked.

Checking the error from devm_add_action() is not enough.  The api
currently relies on the fact that the percpu_ref it is using is killed by
the time the devm_memremap_pages_release() is run.  Rather than continue
this awkward situation, offload the responsibility of killing the
percpu_ref to devm_memremap_pages_release() directly.  This allows
devm_memremap_pages() to do the right thing relative to init failures and
shutdown.

Without this change we could fail to register the teardown of
devm_memremap_pages().  The likelihood of hitting this failure is tiny as
small memory allocations almost always succeed.  However, the impact of
the failure is large given any future reconfiguration, or disable/enable,
of an nvdimm namespace will fail forever as subsequent calls to
devm_memremap_pages() will fail to setup the pgmap_radix since there will
be stale entries for the physical address range.

An argument could be made to require that the ->kill() operation be set in
the @pgmap arg rather than passed in separately.  However, it helps code
readability, tracking the lifetime of a given instance, to be able to grep
the kill routine directly at the devm_memremap_pages() call site.

Link: http://lkml.kernel.org/r/154275558526.76910.7535251937849268605.stgit@dwillia2-desk3.amr.corp.intel.com
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Fixes: e8d5134833 ("memremap: change devm_memremap_pages interface...")
Reviewed-by: "Jérôme Glisse" <jglisse@redhat.com>
Reported-by: Logan Gunthorpe <logang@deltatee.com>
Reviewed-by: Logan Gunthorpe <logang@deltatee.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Cc: Balbir Singh <bsingharora@gmail.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/dax/pmem.c

@@ -48,9 +48,8 @@ static void dax_pmem_percpu_exit(void *data)
 	percpu_ref_exit(ref);
 }
 
-static void dax_pmem_percpu_kill(void *data)
+static void dax_pmem_percpu_kill(struct percpu_ref *ref)
 {
-	struct percpu_ref *ref = data;
 	struct dax_pmem *dax_pmem = to_dax_pmem(ref);
 
 	dev_dbg(dax_pmem->dev, "trace\n");
@@ -112,17 +111,10 @@ static int dax_pmem_probe(struct device *dev)
 	}
 
 	dax_pmem->pgmap.ref = &dax_pmem->ref;
+	dax_pmem->pgmap.kill = dax_pmem_percpu_kill;
 	addr = devm_memremap_pages(dev, &dax_pmem->pgmap);
-	if (IS_ERR(addr)) {
-		devm_remove_action(dev, dax_pmem_percpu_exit, &dax_pmem->ref);
-		percpu_ref_exit(&dax_pmem->ref);
+	if (IS_ERR(addr))
 		return PTR_ERR(addr);
-	}
-
-	rc = devm_add_action_or_reset(dev, dax_pmem_percpu_kill,
-							&dax_pmem->ref);
-	if (rc)
-		return rc;
 
 	/* adjust the dax_region resource to the start of data */
 	memcpy(&res, &dax_pmem->pgmap.res, sizeof(res));