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Vlastimil Babka 64a94c550c mm, compaction: fully assume capture is not NULL in compact_zone_order()
commit 6467552ca6 upstream.

Dan reports:

The patch 5e1f0f098b: "mm, compaction: capture a page under direct
compaction" from Mar 5, 2019, leads to the following Smatch complaint:

    mm/compaction.c:2321 compact_zone_order()
     error: we previously assumed 'capture' could be null (see line 2313)

mm/compaction.c
  2288  static enum compact_result compact_zone_order(struct zone *zone, int order,
  2289                  gfp_t gfp_mask, enum compact_priority prio,
  2290                  unsigned int alloc_flags, int classzone_idx,
  2291                  struct page **capture)
                                      ^^^^^^^

  2313		if (capture)
                    ^^^^^^^
Check for NULL

  2314			current->capture_control = &capc;
  2315
  2316		ret = compact_zone(&cc, &capc);
  2317
  2318		VM_BUG_ON(!list_empty(&cc.freepages));
  2319		VM_BUG_ON(!list_empty(&cc.migratepages));
  2320
  2321		*capture = capc.page;
                ^^^^^^^^
Unchecked dereference.

  2322		current->capture_control = NULL;
  2323

In practice this is not an issue, as the only caller path passes non-NULL
capture:

__alloc_pages_direct_compact()
  struct page *page = NULL;
  try_to_compact_pages(capture = &page);
    compact_zone_order(capture = capture);

So let's remove the unnecessary check, which should also make Smatch happy.

Fixes: 5e1f0f098b ("mm, compaction: capture a page under direct compaction")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Suggested-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Mel Gorman <mgorman@techsingularity.net>
Link: http://lkml.kernel.org/r/18b0df3c-0589-d96c-23fa-040798fee187@suse.cz
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2020-07-09 09:37:57 +02:00
arch MIPS: Add missing EHB in mtc0 -> mfc0 sequence for DSPen 2020-07-09 09:37:56 +02:00
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crypto crypto: af_alg - fix use-after-free in af_alg_accept() due to bh_lock_sock() 2020-07-09 09:37:52 +02:00
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drivers irqchip/gic: Atomically update affinity 2020-07-09 09:37:56 +02:00
fs cifs: Fix the target file was deleted when rename failed. 2020-07-09 09:37:55 +02:00
include crypto: af_alg - fix use-after-free in af_alg_accept() due to bh_lock_sock() 2020-07-09 09:37:52 +02:00
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mm mm, compaction: fully assume capture is not NULL in compact_zone_order() 2020-07-09 09:37:57 +02:00
net rxrpc: Fix afs large storage transmission performance drop 2020-07-09 09:37:52 +02:00
samples samples/vfs: avoid warning in statx override 2020-07-09 09:37:54 +02:00
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sound Revert "ALSA: usb-audio: Improve frames size computation" 2020-07-09 09:37:55 +02:00
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