[lkml]   [2020]   [Nov]   [21]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
Patch in this message
Subject[PATCH 1/1] mm: compaction: avoid fast_isolate_around() to set pageblock_skip on reserved pages
A corollary issue was fixed in
e577c8b64d58fe307ea4d5149d31615df2d90861. A second issue remained in

page:ffffea0000aa0000 refcount:1 mapcount:0 mapping:000000002243743b index:0x0
flags: 0x1fffe000001000(reserved)

73a6e474cb376921a311786652782155eac2fdf0 was applied to supposedly the
second issue, but I still reproduced it twice with v5.9 on two
different systems:

page:0000000062b3e92f refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x39800
flags: 0x1000(reserved)
page:000000002a7114f8 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x7a200
flags: 0x1fff000000001000(reserved)

I actually never reproduced it until v5.9, but it's still the same bug
as it was reported first for v5.7.

See the page is "reserved" in all 3 cases. In the last two crashes
with the pfn:

pfn 0x39800 -> 0x39800000 min_pfn hit non-RAM:

39639000-39814fff : Unknown E820 type

pfn 0x7a200 -> 0x7a200000 min_pfn hit non-RAM:

7a17b000-7a216fff : Unknown E820 type

This actually seems a false positive bugcheck, the page structures are
valid and the zones are correct, just it's non-RAM but setting
pageblockskip should do no harm. However it's possible to solve the
crash without lifting the bugcheck, by enforcing the invariant that
the free_pfn cursor doesn't point to reserved pages (which would be
otherwise implicitly achieved through the PageBuddy check, except in
the new fast_isolate_around() path).

Fixes: 5a811889de10 ("mm, compaction: use free lists to quickly locate a migration target")
Signed-off-by: Andrea Arcangeli <>
mm/compaction.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/mm/compaction.c b/mm/compaction.c
index 13cb7a961b31..d17e69549d34 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -1433,7 +1433,10 @@ fast_isolate_freepages(struct compact_control *cc)
page = pageblock_pfn_to_page(min_pfn,
- cc->free_pfn = min_pfn;
+ if (likely(!PageReserved(page)))
+ cc->free_pfn = min_pfn;
+ else
+ page = NULL;
 \ /
  Last update: 2020-11-21 20:47    [W:0.212 / U:1.184 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site