[RFC PATCH v2 5/5] mm/slub: do not create dma-kmalloc if no managed pages in DMA zone

[Baoquan He <bhe@redhat.com>]

Dma-kmalloc will be created as long as CONFIG_ZONE_DMA is enabled.
However, it will fail if DMA zone has no managed pages. The failure
can be seen in kdump kernel of x86_64 as below:

 CPU: 0 PID: 65 Comm: kworker/u2:1 Not tainted 5.14.0-rc2+ #9
 Hardware name: Intel Corporation SandyBridge Platform/To be filled by O.E.M., BIOS RMLSDP.86I.R2.28.D690.1306271008 06/27/2013
 Workqueue: events_unbound async_run_entry_fn
 Call Trace:
  dump_stack_lvl+0x57/0x72
  warn_alloc.cold+0x72/0xd6
  __alloc_pages_slowpath.constprop.0+0xf56/0xf70
  __alloc_pages+0x23b/0x2b0
  allocate_slab+0x406/0x630
  ___slab_alloc+0x4b1/0x7e0
  ? sr_probe+0x200/0x600
  ? lock_acquire+0xc4/0x2e0
  ? fs_reclaim_acquire+0x4d/0xe0
  ? lock_is_held_type+0xa7/0x120
  ? sr_probe+0x200/0x600
  ? __slab_alloc+0x67/0x90
  __slab_alloc+0x67/0x90
  ? sr_probe+0x200/0x600
  ? sr_probe+0x200/0x600
  kmem_cache_alloc_trace+0x259/0x270
  sr_probe+0x200/0x600
  ......
  bus_probe_device+0x9f/0xb0
  device_add+0x3d2/0x970
  ......
  __scsi_add_device+0xea/0x100
  ata_scsi_scan_host+0x97/0x1d0
  async_run_entry_fn+0x30/0x130
  process_one_work+0x2b0/0x5c0
  worker_thread+0x55/0x3c0
  ? process_one_work+0x5c0/0x5c0
  kthread+0x149/0x170
  ? set_kthread_struct+0x40/0x40
  ret_from_fork+0x22/0x30
 Mem-Info:
 ......

The above failure happened when calling kmalloc() to allocate buffer with
GFP_DMA. It requests to allocate slab page from DMA zone while no managed
pages in there.
 sr_probe()
 --> get_capabilities()
     --> buffer = kmalloc(512, GFP_KERNEL | GFP_DMA);

The DMA zone should be checked if it has managed pages, then try to create
dma-kmalloc.

Signed-off-by: Baoquan He <bhe@redhat.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Vlastimil Babka <vbabka@suse.cz>

---
 mm/slab_common.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/mm/slab_common.c b/mm/slab_common.c
index 1c673c323baf..22350bef3bae 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -911,10 +911,16 @@ void __init create_kmalloc_caches(slab_flags_t flags)
 	slab_state = UP;
 
 #ifdef CONFIG_ZONE_DMA
+	bool managed_dma = has_managed_dma();
+
 	for (i = 0; i <= KMALLOC_SHIFT_HIGH; i++) {
 		struct kmem_cache *s = kmalloc_caches[KMALLOC_NORMAL][i];
 
 		if (s) {
+			if (!managed_dma) {
+				kmalloc_caches[KMALLOC_DMA][i] = kmalloc_caches[KMALLOC_NORMAL][i];
+				continue;
+			}
 			kmalloc_caches[KMALLOC_DMA][i] = create_kmalloc_cache(
 				kmalloc_info[i].name[KMALLOC_DMA],
 				kmalloc_info[i].size,
-- 
2.17.2