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authorHugh Dickins <hughd@google.com>2011-03-22 16:33:07 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2011-03-22 17:44:04 -0700
commit5b280c0cc70062967bb9d630b216375b18db3a0b (patch)
tree6242d234d08fdd433b99c425e25f6562cd51cd0f /mm
parent9d8aa4ea855e0d64bb6926acb5618e6d1e2ed344 (diff)
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mm: don't return 0 too early from find_get_pages()
Callers of find_get_pages(), or its wrapper pagevec_lookup() - notably truncate_inode_pages_range() - stop looking further when it returns 0. But if an interrupt comes just after its radix_tree_gang_lookup_slot(), especially if we have preemptible RCU enabled, isn't it conceivable that all 14 pages returned could be removed from the page cache by shrink_page_list(), before find_get_pages() gets to process them? So causing it to return 0 although there may be plenty more pages beyond. Make find_get_pages() and find_get_pages_tag() check for this unlikely case, and restart should it occur; but callers of find_get_pages_contig() have no such expectation, it's okay for that to return 0 early. I have not seen this in practice, just worried by the possibility. Signed-off-by: Hugh Dickins <hughd@google.com> Cc: Nick Piggin <npiggin@kernel.dk> Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Wu Fengguang <fengguang.wu@intel.com> Cc: Salman Qazi <sqazi@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm')
-rw-r--r--mm/filemap.c14
1 files changed, 14 insertions, 0 deletions
diff --git a/mm/filemap.c b/mm/filemap.c
index a293181..f807afd 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -885,6 +885,13 @@ repeat:
pages[ret] = page;
ret++;
}
+
+ /*
+ * If all entries were removed before we could secure them,
+ * try again, because callers stop trying once 0 is returned.
+ */
+ if (unlikely(!ret && nr_found))
+ goto restart;
rcu_read_unlock();
return ret;
}
@@ -1004,6 +1011,13 @@ repeat:
pages[ret] = page;
ret++;
}
+
+ /*
+ * If all entries were removed before we could secure them,
+ * try again, because callers stop trying once 0 is returned.
+ */
+ if (unlikely(!ret && nr_found))
+ goto restart;
rcu_read_unlock();
if (ret)