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>
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14
mm/filemap.c
14
mm/filemap.c
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@ -885,6 +885,13 @@ repeat:
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pages[ret] = page;
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ret++;
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}
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/*
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* If all entries were removed before we could secure them,
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* try again, because callers stop trying once 0 is returned.
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*/
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if (unlikely(!ret && nr_found))
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goto restart;
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rcu_read_unlock();
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return ret;
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}
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@ -1004,6 +1011,13 @@ repeat:
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pages[ret] = page;
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ret++;
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}
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/*
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* If all entries were removed before we could secure them,
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* try again, because callers stop trying once 0 is returned.
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*/
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if (unlikely(!ret && nr_found))
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goto restart;
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rcu_read_unlock();
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if (ret)
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