The iterator functions pcpu_next_md_free_region and pcpu_next_fit_region use the block offset to determine if they have checked the area in the prior iteration. However, this causes an issue when the block offset is greater than subsequent block contig hints. If within the iterator it moves to check subsequent blocks, it may fail in the second predicate due to the block offset not being cleared. Thus, this causes the allocator to skip over blocks leading to false failures when allocating from the reserved chunk. While this happens in the general case as well, it will only fail if it cannot allocate a new chunk. This patch resets the block offset to 0 to pass the second predicate when checking subseqent blocks within the iterator function. Signed-off-by: Dennis Zhou <dennisszhou@xxxxxxxxx> Reported-by: Luis Henriques <lhenriques@xxxxxxxx> --- mm/percpu.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/mm/percpu.c b/mm/percpu.c index 59d44d6..aa121ce 100644 --- a/mm/percpu.c +++ b/mm/percpu.c @@ -353,6 +353,8 @@ static void pcpu_next_md_free_region(struct pcpu_chunk *chunk, int *bit_off, block->contig_hint_start); return; } + /* reset to satisfy the second predicate above */ + block_off = 0; *bits = block->right_free; *bit_off = (i + 1) * PCPU_BITMAP_BLOCK_BITS - block->right_free; @@ -407,6 +409,8 @@ static void pcpu_next_fit_region(struct pcpu_chunk *chunk, int alloc_bits, *bit_off = pcpu_block_off_to_off(i, block->first_free); return; } + /* reset to satisfy the second predicate above */ + block_off = 0; *bit_off = ALIGN(PCPU_BITMAP_BLOCK_BITS - block->right_free, align); -- 1.8.3.1 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
