early_pfn_to_nid historically was inherently not SMP safe but only
used during boot which is inherently single threaded or during hotplug
which is protected by a giant mutex. With deferred memory initialisation
there was a thread-safe version introduced and the early_pfn_to_nid
would trigger a BUG_ON if used unsafely. Memory hotplug hit that check.
This patch makes early_pfn_to_nid introduces a lock to make it safe to
use during hotplug.
Reported-and-tested-by: Alex Ng <alexng@xxxxxxxxxxxxx>
Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
---
mm/page_alloc.c | 19 ++++++++++++-------
1 file changed, 12 insertions(+), 7 deletions(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 94e2599830c2..f1e841c67b7a 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -982,21 +982,26 @@ static void __init __free_pages_boot_core(struct page *page,
#if defined(CONFIG_HAVE_ARCH_EARLY_PFN_TO_NID) || \
defined(CONFIG_HAVE_MEMBLOCK_NODE_MAP)
-/* Only safe to use early in boot when initialisation is single-threaded */
+
static struct mminit_pfnnid_cache early_pfnnid_cache __meminitdata;
int __meminit early_pfn_to_nid(unsigned long pfn)
{
+ static DEFINE_SPINLOCK(early_pfn_lock);
int nid;
- /* The system will behave unpredictably otherwise */
- BUG_ON(system_state != SYSTEM_BOOTING);
+ /* Avoid locking overhead during boot but hotplug must lock */
+ if (system_state != SYSTEM_BOOTING)
+ spin_lock(&early_pfn_lock);
nid = __early_pfn_to_nid(pfn, &early_pfnnid_cache);
- if (nid >= 0)
- return nid;
- /* just returns 0 */
- return 0;
+ if (nid < 0)
+ nid = 0;
+
+ if (system_state != SYSTEM_BOOTING)
+ spin_unlock(&early_pfn_lock);
+
+ return nid;
}
#endif
--
2.4.3
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