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[188.28.125.106]) by smtp.gmail.com with ESMTPSA id h9-20020a5d4309000000b002102af52a2csm33934618wrq.9.2022.06.10.03.22.41 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 10 Jun 2022 03:22:41 -0700 (PDT) Message-ID: <37d73555-197b-29e1-d2cc-b7313501a394@gmail.com> Date: Fri, 10 Jun 2022 11:21:29 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.9.1 Subject: Re: [PATCH v3] io_uring: switch cancel_hash to use per entry spinlock Content-Language: en-US To: Hao Xu , io-uring@vger.kernel.org Cc: Jens Axboe References: <20220608111259.659536-1-hao.xu@linux.dev> From: Pavel Begunkov In-Reply-To: <20220608111259.659536-1-hao.xu@linux.dev> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On 6/8/22 12:12, Hao Xu wrote: > From: Hao Xu > > Add a new io_hash_bucket structure so that each bucket in cancel_hash > has separate spinlock. Use per entry lock for cancel_hash, this removes > some completion lock invocation and remove contension between different > cancel_hash entries. > > Signed-off-by: Hao Xu > --- > > v1->v2: > - Add per entry lock for poll/apoll task work code which was missed > in v1 > - add an member in io_kiocb to track req's indice in cancel_hash > > v2->v3: > - make struct io_hash_bucket align with cacheline to avoid cacheline > false sharing. > - re-calculate hash value when deleting an entry from cancel_hash. > (cannot leverage struct io_poll to store the indice since it's > already 64 Bytes) > > io_uring/cancel.c | 14 +++++++-- > io_uring/cancel.h | 6 ++++ > io_uring/fdinfo.c | 9 ++++-- > io_uring/io_uring.c | 8 +++-- > io_uring/io_uring_types.h | 2 +- > io_uring/poll.c | 64 +++++++++++++++++++++------------------ > 6 files changed, 65 insertions(+), 38 deletions(-) > > diff --git a/io_uring/cancel.c b/io_uring/cancel.c > index 83cceb52d82d..bced5d6b9294 100644 > --- a/io_uring/cancel.c > +++ b/io_uring/cancel.c > @@ -93,14 +93,14 @@ int io_try_cancel(struct io_kiocb *req, struct io_cancel_data *cd) > if (!ret) > return 0; > > - spin_lock(&ctx->completion_lock); > ret = io_poll_cancel(ctx, cd); > if (ret != -ENOENT) > goto out; > + spin_lock(&ctx->completion_lock); > if (!(cd->flags & IORING_ASYNC_CANCEL_FD)) > ret = io_timeout_cancel(ctx, cd); > -out: > spin_unlock(&ctx->completion_lock); > +out: > return ret; > } > > @@ -192,3 +192,13 @@ int io_async_cancel(struct io_kiocb *req, unsigned int issue_flags) > io_req_set_res(req, ret, 0); > return IOU_OK; > } > + > +inline void init_hash_table(struct io_hash_bucket *hash_table, unsigned size) Not inline, it can break builds > diff --git a/io_uring/cancel.h b/io_uring/cancel.h > index 4f35d8696325..b57d6706f84d 100644 > --- a/io_uring/cancel.h > +++ b/io_uring/cancel.h > @@ -4,3 +4,9 @@ int io_async_cancel_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe); > int io_async_cancel(struct io_kiocb *req, unsigned int issue_flags); > > int io_try_cancel(struct io_kiocb *req, struct io_cancel_data *cd); > +inline void init_hash_table(struct io_hash_bucket *hash_table, unsigned size); And this inline as well > diff --git a/io_uring/poll.c b/io_uring/poll.c > index 0df5eca93b16..515f1727e3c6 100644 > --- a/io_uring/poll.c > +++ b/io_uring/poll.c [...] > static struct io_kiocb *io_poll_find(struct io_ring_ctx *ctx, bool poll_only, > struct io_cancel_data *cd) > - __must_hold(&ctx->completion_lock) > { > - struct hlist_head *list; > struct io_kiocb *req; > > - list = &ctx->cancel_hash[hash_long(cd->data, ctx->cancel_hash_bits)]; > - hlist_for_each_entry(req, list, hash_node) { > + u32 index = hash_long(cd->data, ctx->cancel_hash_bits); > + struct io_hash_bucket *hb = &ctx->cancel_hash[index]; > + > + spin_lock(&hb->lock); > + hlist_for_each_entry(req, &hb->list, hash_node) { > if (cd->data != req->cqe.user_data) > continue; > if (poll_only && req->opcode != IORING_OP_POLL_ADD) > @@ -569,47 +577,48 @@ static struct io_kiocb *io_poll_find(struct io_ring_ctx *ctx, bool poll_only, > continue; > req->work.cancel_seq = cd->seq; > } > + spin_unlock(&hb->lock); The problem here is that after you unlock, nothing keeps the request alive. Before it was more like lock(completion_lock); req = poll_find(); cancel_poll(req); unlock(completion_lock); and was relying on all of this happening under ->completion_lock. Now following io_poll_disarm() and/or io_poll_cancel_req() race. Same with io_poll_file_find(). Should be fine apart from this -- Pavel Begunkov