| Message ID | 20240902130329.3787024-3-yukuai1@huaweicloud.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | block, bfq: fix corner cases related to bfqq merging | expand |
On Mon 02-09-24 21:03:27, Yu Kuai wrote: > From: Yu Kuai <yukuai3@huawei.com> > > Consider the following merge chain: > > Process 1 Process 2 Process 3 Process 4 > (BIC1) (BIC2) (BIC3) (BIC4) > Λ | | | > \--------------\ \-------------\ \-------------\| > V V V > bfqq1--------->bfqq2---------->bfqq3----------->bfqq4 > > IO from Process 1 will get bfqf2 from BIC1 first, then > bfq_setup_cooperator() will found bfqq2 already merged to bfqq3 and then > handle this IO from bfqq3. However, the merge chain can be much deeper > and bfqq3 can be merged to other bfqq as well. > > Fix this problem by iterating to the last bfqq in > bfq_setup_cooperator(). > > Fixes: 36eca8948323 ("block, bfq: add Early Queue Merge (EQM)") > Signed-off-by: Yu Kuai <yukuai3@huawei.com> Good catch. Feel free to add: Reviewed-by: Jan Kara <jack@suse.cz> Honza > --- > block/bfq-iosched.c | 8 ++++++-- > 1 file changed, 6 insertions(+), 2 deletions(-) > > diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c > index 83adac3e71db..ffaa0d56328a 100644 > --- a/block/bfq-iosched.c > +++ b/block/bfq-iosched.c > @@ -2911,8 +2911,12 @@ bfq_setup_cooperator(struct bfq_data *bfqd, struct bfq_queue *bfqq, > struct bfq_iocq_bfqq_data *bfqq_data = &bic->bfqq_data[a_idx]; > > /* if a merge has already been setup, then proceed with that first */ > - if (bfqq->new_bfqq) > - return bfqq->new_bfqq; > + new_bfqq = bfqq->new_bfqq; > + if (new_bfqq) { > + while (new_bfqq->new_bfqq) > + new_bfqq = new_bfqq->new_bfqq; > + return new_bfqq; > + } > > /* > * Check delayed stable merge for rotational or non-queueing > -- > 2.39.2 >
diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c index 83adac3e71db..ffaa0d56328a 100644 --- a/block/bfq-iosched.c +++ b/block/bfq-iosched.c @@ -2911,8 +2911,12 @@ bfq_setup_cooperator(struct bfq_data *bfqd, struct bfq_queue *bfqq, struct bfq_iocq_bfqq_data *bfqq_data = &bic->bfqq_data[a_idx]; /* if a merge has already been setup, then proceed with that first */ - if (bfqq->new_bfqq) - return bfqq->new_bfqq; + new_bfqq = bfqq->new_bfqq; + if (new_bfqq) { + while (new_bfqq->new_bfqq) + new_bfqq = new_bfqq->new_bfqq; + return new_bfqq; + } /* * Check delayed stable merge for rotational or non-queueing