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Mon, 02 Nov 2026 04:49:09 -0800 (PST) Received: from localhost ([140.209.217.212]) by smtp.gmail.com with ESMTPSA id 2adb3069b0e04-5bfe04ee003sm1638014e87.7.2026.11.02.04.49.08 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 02 Nov 2026 04:49:09 -0800 (PST) Date: Mon, 2 Nov 2026 13:49:05 +0100 From: Jiri Pirko To: Yeoreum Yun Cc: linux-coco@lists.linux.dev, linux-kernel@vger.kernel.org, linux-api@vger.kernel.org, x86@kernel.org, kvm@vger.kernel.org, linux-doc@vger.kernel.org, jgg@ziepe.ca, david.quigley@intel.com, lukas@wunner.de, ksinyuk@kernel.org, rodrigo.vivi@intel.com, cedric.xing@intel.com, sameo@meta.com, drdeeglaze@gmail.com, James.Bottomley@hansenpartnership.com, aik@amd.com, jpiotrowski@nvidia.com, qinkun@google.com, pgonda@google.com, jic23@kernel.org, alistair.francis@wdc.com, ankita@nvidia.com, suzuki.poulose@arm.com, kas@kernel.org, rick.p.edgecombe@intel.com, elena.reshetova@intel.com, dave.hansen@linux.intel.com, sathyanarayanan.kuppuswamy@linux.intel.com, peter.fang@intel.com Subject: Re: [PATCH RFC 10/20] ctlv: Prepare event queue support Message-ID: References: <20261015145053.3664509-1-jiri@resnulli.us> <20261015145053.3664509-11-jiri@resnulli.us> X-Mailing-List: linux-api@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Tue, Oct 27, 2026 at 01:38:21PM +0100, yeoreum.yun@arm.com wrote: >Hi Jiri, > > >[...] > >> +int ctlv_event_emit(struct ctlv_op_ctx *ctx) >> +{ >> + struct ctlv_device *ctlvdev = ctx->ctlvdev; >> + struct ctlv_event_record *rec, *next; >> + struct ctlv_file *cfile; >> + u32 len, wanted = 0; >> + LIST_HEAD(spare); >> + int ret; >> + >> + if (WARN_ON_ONCE(ctx->file)) >> + return -EINVAL; >> + ret = ctlv_event_finish(ctx); >> + if (ret) >> + goto out_free; >> + >> + len = sizeof(struct ctlv_event_hdr) + CTLV_ALIGN(ctx->output.root->len); >> + scoped_guard(spinlock, &ctlvdev->events_lock) { >> + if (ctlvdev->dead_announced) >> + goto out_free; >> + list_for_each_entry(cfile, &ctlvdev->files, node) >> + if (test_bit(ctx->op->event_index, cfile->subscribed)) >> + wanted++; >> + } > >Suppose at the time of here, the number of subscriber is 1. >However, before calling the ctlv_event_deliver(), another task hold the >event_lock() to register new subscriber. for example: > > >Task 1 (emit) Task 2 (new subscriber B) > >wanted = 1 >unlock events_lock. > Register subscription. >allocate one record >ctlv_event_delver() > > grab events_lock. > Deliver former subscribe event to old one. > new subscriber B will call ctlv_event_queue_event() with NULL. > >When this happens, new subscriber B would receive overflow event >via ctlv_event_queue_dropped() though it was registered right before. > >Is this intended? It doesn't make sense that subscribe B receives >the overflow event in this situation... Not intended. Will fix. > > >> + if (wanted) { >> + ctlv_event_copies(ctx, len, &spare, wanted); >> + ctlv_event_deliver(ctx, &spare); >> + list_for_each_entry_safe(rec, next, &spare, node) >> + kfree(rec); >> + } >> + >> +out_free: >> + ctlv_event_free(ctx); >> + return ret; >> +} >> +EXPORT_SYMBOL_NS_GPL(ctlv_event_emit, "CTLV"); >> + > >[...] > >Thanks! > >-- >Sincerely, >Yeoreum Yun