mm: don't return 0 too early from find_get_pages()
authorHugh Dickins <hughd@google.com>
Tue, 22 Mar 2011 23:33:07 +0000 (16:33 -0700)
committerLinus Torvalds <torvalds@linux-foundation.org>
Wed, 23 Mar 2011 00:44:04 +0000 (17:44 -0700)
commit5b280c0cc70062967bb9d630b216375b18db3a0b
tree6242d234d08fdd433b99c425e25f6562cd51cd0f
parent9d8aa4ea855e0d64bb6926acb5618e6d1e2ed344
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>
mm/filemap.c