Commit 7ace9917 authored Aug 06, 2015 by Mel Gorman Committed by Linus Torvalds Aug 07, 2015

mm, meminit: allow early_pfn_to_nid to be used during runtime



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.

Signed-off-by: Mel Gorman <mgorman@suse.de>
Reported-by: Alex Ng <alexng@microsoft.com>
Tested-by: Alex Ng <alexng@microsoft.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Nicolai Stange <nicstange@gmail.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent de54b9ac

mm/page_alloc.c

+8 −8

Original line number	Diff line number	Diff line
		@@ -981,21 +981,21 @@ 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);

		spin_lock(&early_pfn_lock);
		nid = __early_pfn_to_nid(pfn, &early_pfnnid_cache);
		if (nid >= 0)
		if (nid < 0)
		nid = 0;
		spin_unlock(&early_pfn_lock);

		return nid;
		/* just returns 0 */
		return 0;
		}
		#endif

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