> -----Original Message----- > From: dennis@xxxxxxxxxx [mailto:dennis@xxxxxxxxxx] > Sent: 2019年3月5日 2:57 > To: Peng Fan <peng.fan@xxxxxxx> > Cc: tj@xxxxxxxxxx; cl@xxxxxxxxx; linux-mm@xxxxxxxxx; > linux-kernel@xxxxxxxxxxxxxxx; van.freenix@xxxxxxxxx > Subject: Re: [PATCH 2/2] percpu: pcpu_next_md_free_region: inclusive check > for PCPU_BITMAP_BLOCK_BITS > > Hi Peng, > > On Mon, Mar 04, 2019 at 10:33:55AM +0000, Peng Fan wrote: > > If the block [contig_hint_start, contig_hint_start + contig_hint) > > matches block->right_free area, need use "<=", not "<". > > > > Signed-off-by: Peng Fan <peng.fan@xxxxxxx> > > --- > > > > V1: > > Based on > https://emea01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fpatc > hwork.kernel.org%2Fcover%2F10832459%2F&data=02%7C01%7Cpeng.f > an%40nxp.com%7C6546dfcc85f0492d7c7508d6a0d33076%7C686ea1d3bc2b > 4c6fa92cd99c5c301635%7C0%7C0%7C636873226241185534&sdata=9 > azIw8vXJ8eqqd0T0znmEN6jR2cWhFghKBfg0zIJMDM%3D&reserved=0 > applied linux-next > > boot test on qemu aarch64 > > > > mm/percpu.c | 3 ++- > > 1 file changed, 2 insertions(+), 1 deletion(-) > > > > diff --git a/mm/percpu.c b/mm/percpu.c index > > 5ee90fc34ea3..0f91f1d883c6 100644 > > --- a/mm/percpu.c > > +++ b/mm/percpu.c > > @@ -390,7 +390,8 @@ static void pcpu_next_md_free_region(struct > pcpu_chunk *chunk, int *bit_off, > > */ > > *bits = block->contig_hint; > > if (*bits && block->contig_hint_start >= block_off && > > - *bits + block->contig_hint_start < PCPU_BITMAP_BLOCK_BITS) > { > > + *bits + block->contig_hint_start <= > > + PCPU_BITMAP_BLOCK_BITS) { > > *bit_off = pcpu_block_off_to_off(i, > > block->contig_hint_start); > > return; > > -- > > 2.16.4 > > > > This is wrong. This iterator is for updating contig hints and not for > finding fit. I missed to consider the case the when contig_hint_start matches right_free area, the right_free area will be take into consideration into next loop. > > Have you tried reproducing and proving the issue you are seeing? In > general, making changes to percpu carries a lot of risk. I really only > want to be taking code that is provably solving a problem and not > supported by just code inspection. Boot testing for a change like this > is really not enough as we need to be sure changes like these are > correct. I'll be careful for future patches. Thanks, Peng. > > Thanks, > Dennis
