[PATCH] mm/mremap_pages: Fix static key devmap_managed_key updates

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commit 6f42193fd86e ("memremap: don't use a separate devm action for
devmap_managed_enable_get") changed the static key updates such that we
now call devmap_managed_enable_put() without doing the equivalent
devmap_managed_enable_get().

devmap_managed_enable_get() is only called for MEMORY_DEVICE_PRIVATE and
MEMORY_DEVICE_FS_DAX, But memunmap_pages() get called for other pgmap
types too. This results in the below warning when switching between
system-ram and devdax mode for devdax namespace.

 jump label: negative count!
 WARNING: CPU: 52 PID: 1335 at kernel/jump_label.c:235 static_key_slow_try_dec+0x88/0xa0
 Modules linked in:
 ....

 NIP [c000000000433318] static_key_slow_try_dec+0x88/0xa0
 LR [c000000000433314] static_key_slow_try_dec+0x84/0xa0
 Call Trace:
 [c000000025c1f660] [c000000000433314] static_key_slow_try_dec+0x84/0xa0 (unreliable)
 [c000000025c1f6d0] [c000000000433664] __static_key_slow_dec_cpuslocked+0x34/0xd0
 [c000000025c1f700] [c0000000004337a4] static_key_slow_dec+0x54/0xf0
 [c000000025c1f770] [c00000000059c49c] memunmap_pages+0x36c/0x500
 [c000000025c1f820] [c000000000d91d10] devm_action_release+0x30/0x50
 [c000000025c1f840] [c000000000d92e34] release_nodes+0x2f4/0x3e0
 [c000000025c1f8f0] [c000000000d8b15c] device_release_driver_internal+0x17c/0x280
 [c000000025c1f930] [c000000000d883a4] bus_remove_device+0x124/0x210
 [c000000025c1f9b0] [c000000000d80ef4] device_del+0x1d4/0x530
 [c000000025c1fa70] [c000000000e341e8] unregister_dev_dax+0x48/0xe0
 [c000000025c1fae0] [c000000000d91d10] devm_action_release+0x30/0x50
 [c000000025c1fb00] [c000000000d92e34] release_nodes+0x2f4/0x3e0
 [c000000025c1fbb0] [c000000000d8b15c] device_release_driver_internal+0x17c/0x280
 [c000000025c1fbf0] [c000000000d87000] unbind_store+0x130/0x170
 [c000000025c1fc30] [c000000000d862a0] drv_attr_store+0x40/0x60
 [c000000025c1fc50] [c0000000006d316c] sysfs_kf_write+0x6c/0xb0
 [c000000025c1fc90] [c0000000006d2328] kernfs_fop_write+0x118/0x280
 [c000000025c1fce0] [c0000000005a79f8] vfs_write+0xe8/0x2a0
 [c000000025c1fd30] [c0000000005a7d94] ksys_write+0x84/0x140
 [c000000025c1fd80] [c00000000003a430] system_call_exception+0x120/0x270
 [c000000025c1fe20] [c00000000000c540] system_call_common+0xf0/0x27c

Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: Sachin Sant <sachinp@xxxxxxxxxxxxxxxxxx>
Cc: linux-nvdimm@xxxxxxxxxxxx
Cc: Ira Weiny <ira.weiny@xxxxxxxxx>
Cc: Jason Gunthorpe <jgg@xxxxxxxxxxxx>
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxx>
---
 mm/memremap.c | 19 +++++++++++++++----
 1 file changed, 15 insertions(+), 4 deletions(-)

diff --git a/mm/memremap.c b/mm/memremap.c
index 73a206d0f645..d4402ff3e467 100644
--- a/mm/memremap.c
+++ b/mm/memremap.c
@@ -158,6 +158,16 @@ void memunmap_pages(struct dev_pagemap *pgmap)
 {
 	unsigned long pfn;
 	int i;
+	bool need_devmap_managed = false;
+
+	switch (pgmap->type) {
+	case MEMORY_DEVICE_PRIVATE:
+	case MEMORY_DEVICE_FS_DAX:
+		need_devmap_managed = true;
+		break;
+	default:
+		break;
+	}
 
 	dev_pagemap_kill(pgmap);
 	for (i = 0; i < pgmap->nr_range; i++)
@@ -169,7 +179,8 @@ void memunmap_pages(struct dev_pagemap *pgmap)
 		pageunmap_range(pgmap, i);
 
 	WARN_ONCE(pgmap->altmap.alloc, "failed to free all reserved pages\n");
-	devmap_managed_enable_put();
+	if (need_devmap_managed)
+		devmap_managed_enable_put();
 }
 EXPORT_SYMBOL_GPL(memunmap_pages);
 
@@ -307,7 +318,7 @@ void *memremap_pages(struct dev_pagemap *pgmap, int nid)
 		.pgprot = PAGE_KERNEL,
 	};
 	const int nr_range = pgmap->nr_range;
-	bool need_devmap_managed = true;
+	bool need_devmap_managed = false;
 	int error, i;
 
 	if (WARN_ONCE(!nr_range, "nr_range must be specified\n"))
@@ -327,6 +338,7 @@ void *memremap_pages(struct dev_pagemap *pgmap, int nid)
 			WARN(1, "Missing owner\n");
 			return ERR_PTR(-EINVAL);
 		}
+		need_devmap_managed = true;
 		break;
 	case MEMORY_DEVICE_FS_DAX:
 		if (!IS_ENABLED(CONFIG_ZONE_DEVICE) ||
@@ -334,13 +346,12 @@ void *memremap_pages(struct dev_pagemap *pgmap, int nid)
 			WARN(1, "File system DAX not supported\n");
 			return ERR_PTR(-EINVAL);
 		}
+		need_devmap_managed = true;
 		break;
 	case MEMORY_DEVICE_GENERIC:
-		need_devmap_managed = false;
 		break;
 	case MEMORY_DEVICE_PCI_P2PDMA:
 		params.pgprot = pgprot_noncached(params.pgprot);
-		need_devmap_managed = false;
 		break;
 	default:
 		WARN(1, "Invalid pgmap type %d\n", pgmap->type);
-- 
2.26.2





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