percpu: do not search past bitmap when allocating an area

BugLink: https://bugs.launchpad.net/bugs/1838824
[ Upstream commit 8c43004af01635cc9fbb11031d070e5e0d327ef2 ]

pcpu_find_block_fit() guarantees that a fit is found within
PCPU_BITMAP_BLOCK_BITS. Iteration is used to determine the first fit as
it compares against the block's contig_hint. This can lead to
incorrectly scanning past the end of the bitmap. The behavior was okay
given the check after for bit_off >= end and the correctness of the
hints from pcpu_find_block_fit().

This patch fixes this by bounding the end offset by the number of bits
in a chunk.

Signed-off-by: Dennis Zhou <dennis@kernel.org>
Reviewed-by: Peng Fan <peng.fan@nxp.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

diff --git a/mm/percpu.c b/mm/percpu.c
index 7014db4ebbf5829e5b3304bfee39118a3514754f..baca22f46a8b59f587674351673376819b46deb8 100644 (file)
--- a/mm/percpu.c
+++ b/mm/percpu.c
@@ -984,7 +984,8 @@ static int pcpu_alloc_area(struct pcpu_chunk *chunk, int alloc_bits,
        /*
         * Search to find a fit.
         */
-       end = start + alloc_bits + PCPU_BITMAP_BLOCK_BITS;
+       end = min_t(int, start + alloc_bits + PCPU_BITMAP_BLOCK_BITS,
+                   pcpu_chunk_map_bits(chunk));
        bit_off = bitmap_find_next_zero_area(chunk->alloc_map, end, start,
                                             alloc_bits, align_mask);
        if (bit_off >= end)