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([2001:b07:6468:f312:c8dd:75d4:99ab:290a]) by smtp.gmail.com with ESMTPSA id b83sm15611651wmd.48.2020.12.11.12.55.41 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 11 Dec 2020 12:55:42 -0800 (PST) Subject: Re: [PATCH 1/1] scsi: fix device removal race vs IO restart callback on resume To: Maxim Levitsky , qemu-devel@nongnu.org References: <20201210125929.1136390-1-mlevitsk@redhat.com> <20201210125929.1136390-2-mlevitsk@redhat.com> From: Paolo Bonzini Message-ID: <2b98f2ef-cab0-3538-dfd9-96fa4ecab0a0@redhat.com> Date: Fri, 11 Dec 2020 21:55:41 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.4.0 MIME-Version: 1.0 In-Reply-To: <20201210125929.1136390-2-mlevitsk@redhat.com> Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=pbonzini@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=63.128.21.124; envelope-from=pbonzini@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, T_SPF_TEMPERROR=0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Fam Zheng Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 10/12/20 13:59, Maxim Levitsky wrote: > There is (mostly theoretical) race between removal of a scsi device and > scsi_dma_restart_bh. > > It used to be easier to hit this race prior to my / Paulo's patch series > that added rcu to scsi bus device handling code, but IMHO this race > should still be possible to hit, at least in theory. > > Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=1854811 > > Fix it anyway with a patch that was proposed by Paulo in the above bugzilla. > > Suggested-by: Paolo Bonzini > Signed-off-by: Maxim Levitsky > --- > hw/scsi/scsi-bus.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/hw/scsi/scsi-bus.c b/hw/scsi/scsi-bus.c > index b901e701f0..edb5c3492a 100644 > --- a/hw/scsi/scsi-bus.c > +++ b/hw/scsi/scsi-bus.c > @@ -170,6 +170,8 @@ static void scsi_dma_restart_bh(void *opaque) > scsi_req_unref(req); > } > aio_context_release(blk_get_aio_context(s->conf.blk)); > + /* Drop the reference that was acquired in scsi_dma_restart_cb */ > + object_unref(OBJECT(s)); > } > > void scsi_req_retry(SCSIRequest *req) > @@ -188,6 +190,8 @@ static void scsi_dma_restart_cb(void *opaque, int running, RunState state) > } > if (!s->bh) { > AioContext *ctx = blk_get_aio_context(s->conf.blk); > + /* The reference is dropped in scsi_dma_restart_bh.*/ > + object_ref(OBJECT(s)); > s->bh = aio_bh_new(ctx, scsi_dma_restart_bh, s); > qemu_bh_schedule(s->bh); > } > Queued, thanks. Paolo