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bh=6akKXCXv6EsoFlkIsJ766ksyO2x05Vult6oh9xmylrY=; b=a0b3Um5PY5IMmF4KC18e9r2jsdlmJtcyNfhNvcxlbXg6HqF/E/n1gagw4+Nta3LdrTN8S6 /iM7M2uNC3BtyyMko8sma7HLxkbtG91UFp19tYc7boWpZg59nmbhWWX6tWM5SSOyiPtCYb qYaDaJcgHSWiHFRapUXfDV7G6FsjDI0= X-MC-Unique: diSlojs9MLGyqGEMRXqDRw-1 From: Hanna Czenczek To: qemu-block@nongnu.org Cc: qemu-devel@nongnu.org, Hanna Czenczek , qemu-stable@nongnu.org, Stefan Hajnoczi , Kevin Wolf , Paolo Bonzini , Fam Zheng Subject: [PATCH 2/2] scsi: Await request purging Date: Fri, 2 Feb 2024 15:47:55 +0100 Message-ID: <20240202144755.671354-3-hreitz@redhat.com> In-Reply-To: <20240202144755.671354-1-hreitz@redhat.com> References: <20240202144755.671354-1-hreitz@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.6 Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Received-SPF: pass client-ip=170.10.133.124; envelope-from=hreitz@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -43 X-Spam_score: -4.4 X-Spam_bar: ---- X-Spam_report: (-4.4 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-2.276, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: qemu-devel-bounces+importer=patchew.org@nongnu.org X-ZohoMail-DKIM: pass (identity @redhat.com) X-ZM-MESSAGEID: 1706885342465100003 Content-Type: text/plain; charset="utf-8" scsi_device_for_each_req_async() currently does not provide any way to be awaited. One of its callers is scsi_device_purge_requests(), which therefore currently does not guarantee that all requests are fully settled when it returns. We want all requests to be settled, because scsi_device_purge_requests() is called through the unrealize path, including the one invoked by virtio_scsi_hotunplug() through qdev_simple_device_unplug_cb(), which most likely assumes that all SCSI requests are done then. In fact, scsi_device_purge_requests() already contains a blk_drain(), but this will not fully await scsi_device_for_each_req_async(), only the I/O requests it potentially cancels (not the non-I/O requests). However, we can have scsi_device_for_each_req_async() increment the BB in-flight counter, and have scsi_device_for_each_req_async_bh() decrement it when it is done. This way, the blk_drain() will fully await all SCSI requests to be purged. This also removes the need for scsi_device_for_each_req_async_bh() to double-check the current context and potentially re-schedule itself, should it now differ from the BB's context: Changing a BB's AioContext with a root node is done through bdrv_try_change_aio_context(), which creates a drained section. With this patch, we keep the BB in-flight counter elevated throughout, so we know the BB's context cannot change. Signed-off-by: Hanna Czenczek Reviewed-by: Stefan Hajnoczi --- hw/scsi/scsi-bus.c | 30 +++++++++++++++++++++--------- 1 file changed, 21 insertions(+), 9 deletions(-) diff --git a/hw/scsi/scsi-bus.c b/hw/scsi/scsi-bus.c index 0a2eb11c56..230313022c 100644 --- a/hw/scsi/scsi-bus.c +++ b/hw/scsi/scsi-bus.c @@ -120,17 +120,13 @@ static void scsi_device_for_each_req_async_bh(void *o= paque) SCSIRequest *next; =20 /* - * If the AioContext changed before this BH was called then reschedule= into - * the new AioContext before accessing ->requests. This can happen when - * scsi_device_for_each_req_async() is called and then the AioContext = is - * changed before BHs are run. + * The BB cannot have changed contexts between this BH being scheduled= and + * now: BBs' AioContexts, when they have a node attached, can only be + * changed via bdrv_try_change_aio_context(), in a drained section. W= hile + * we have the in-flight counter incremented, that drain must block. */ ctx =3D blk_get_aio_context(s->conf.blk); - if (ctx !=3D qemu_get_current_aio_context()) { - aio_bh_schedule_oneshot(ctx, scsi_device_for_each_req_async_bh, - g_steal_pointer(&data)); - return; - } + assert(ctx =3D=3D qemu_get_current_aio_context()); =20 QTAILQ_FOREACH_SAFE(req, &s->requests, next, next) { data->fn(req, data->fn_opaque); @@ -138,11 +134,16 @@ static void scsi_device_for_each_req_async_bh(void *o= paque) =20 /* Drop the reference taken by scsi_device_for_each_req_async() */ object_unref(OBJECT(s)); + + /* Paired with blk_inc_in_flight() in scsi_device_for_each_req_async()= */ + blk_dec_in_flight(s->conf.blk); } =20 /* * Schedule @fn() to be invoked for each enqueued request in device @s. @f= n() * runs in the AioContext that is executing the request. + * Keeps the BlockBackend's in-flight counter incremented until everything= is + * done, so draining it will settle all scheduled @fn() calls. */ static void scsi_device_for_each_req_async(SCSIDevice *s, void (*fn)(SCSIRequest *, void = *), @@ -163,6 +164,8 @@ static void scsi_device_for_each_req_async(SCSIDevice *= s, */ object_ref(OBJECT(s)); =20 + /* Paired with blk_dec_in_flight() in scsi_device_for_each_req_async_b= h() */ + blk_inc_in_flight(s->conf.blk); aio_bh_schedule_oneshot(blk_get_aio_context(s->conf.blk), scsi_device_for_each_req_async_bh, data); @@ -1728,11 +1731,20 @@ static void scsi_device_purge_one_req(SCSIRequest *= req, void *opaque) scsi_req_cancel_async(req, NULL); } =20 +/** + * Cancel all requests, and block until they are deleted. + */ void scsi_device_purge_requests(SCSIDevice *sdev, SCSISense sense) { scsi_device_for_each_req_async(sdev, scsi_device_purge_one_req, NULL); =20 + /* + * Await all the scsi_device_purge_one_req() calls scheduled by + * scsi_device_for_each_req_async(), and all I/O requests that were + * cancelled this way, but may still take a bit of time to settle. + */ blk_drain(sdev->conf.blk); + scsi_device_set_ua(sdev, sense); } =20 --=20 2.43.0