[PATCH] mm: fix regression with deferred struct page init

From: Juergen Gross <jgross@suse.com>
To: xen-devel@lists.xenproject.org, linux-mm@kvack.org,
	linux-kernel@vger.kernel.org
Cc: Juergen Gross <jgross@suse.com>,
	Alexander Duyck <alexander.h.duyck@linux.intel.com>
Subject: [PATCH] mm: fix regression with deferred struct page init
Date: Thu, 20 Jun 2019 18:08:21 +0200	[thread overview]
Message-ID: <20190620160821.4210-1-jgross@suse.com> (raw)

Commit 0e56acae4b4dd4a9 ("mm: initialize MAX_ORDER_NR_PAGES at a time
instead of doing larger sections") is causing a regression on some
systems when the kernel is booted as Xen dom0.

The system will just hang in early boot.

Reason is an endless loop in get_page_from_freelist() in case the first
zone looked at has no free memory. deferred_grow_zone() is always
returning true due to the following code snipplet:

  /* If the zone is empty somebody else may have cleared out the zone */
  if (!deferred_init_mem_pfn_range_in_zone(&i, zone, &spfn, &epfn,
                                           first_deferred_pfn)) {
          pgdat->first_deferred_pfn = ULONG_MAX;
          pgdat_resize_unlock(pgdat, &flags);
          return true;
  }

This in turn results in the loop as get_page_from_freelist() is
assuming forward progress can be made by doing some more struct page
initialization.

Cc: Alexander Duyck <alexander.h.duyck@linux.intel.com>
Fixes: 0e56acae4b4dd4a9 ("mm: initialize MAX_ORDER_NR_PAGES at a time instead of doing larger sections")
Suggested-by: Alexander Duyck <alexander.h.duyck@linux.intel.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
---
 mm/page_alloc.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index d66bc8abe0af..8e3bc949ebcc 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1826,7 +1826,8 @@ deferred_grow_zone(struct zone *zone, unsigned int order)
 						 first_deferred_pfn)) {
 		pgdat->first_deferred_pfn = ULONG_MAX;
 		pgdat_resize_unlock(pgdat, &flags);
-		return true;
+		/* Retry only once. */
+		return first_deferred_pfn != ULONG_MAX;
 	}
 
 	/*
-- 
2.16.4

