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Fri, 02 Feb 2024 09:48:42 -0500 Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-621-_LHxjTqEN_OkezwQkuGIww-1; Fri, 02 Feb 2024 09:48:35 -0500 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.rdu2.redhat.com [10.11.54.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id E69B318A6513; Fri, 2 Feb 2024 14:48:24 +0000 (UTC) Received: from localhost (unknown [10.39.194.28]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 786C8900; Fri, 2 Feb 2024 14:48:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1706885318; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=rxQY+7ko3W9v0eh+vuzLr5ZuuX1slmfDJFHBVuZHIl8=; b=VvqOivEI2uAB9X1xQanwd8HTVZ3bilQiQMAeW0wqr1BmY+OSwNDQm43r3zfvLWWgnS7D7Z kMzIE74b4xv/j6UePJcke/0JeK0Pk6WXe2xpIKP2cFbg4X/AftNW2DcSh2rh471j5pBAU9 wt+rYFXaEEfADohrd6Txr3pgPsjoRxA= X-MC-Unique: _LHxjTqEN_OkezwQkuGIww-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 1/2] block-backend: Allow concurrent context changes Date: Fri, 2 Feb 2024 15:47:54 +0100 Message-ID: <20240202144755.671354-2-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 10.11.54.1 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=170.10.129.124; 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_H2=-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: 1706885372522100003 Content-Type: text/plain; charset="utf-8" Since AioContext locks have been removed, a BlockBackend's AioContext may really change at any time (only exception is that it is often confined to a drained section, as noted in this patch). Therefore, blk_get_aio_context() cannot rely on its root node's context always matching that of the BlockBackend. In practice, whether they match does not matter anymore anyway: Requests can be sent to BDSs from any context, so anyone who requests the BB's context should have no reason to require the root node to have the same context. Therefore, we can and should remove the assertion to that effect. In addition, because the context can be set and queried from different threads concurrently, it has to be accessed with atomic operations. Buglink: https://issues.redhat.com/browse/RHEL-19381 Suggested-by: Kevin Wolf Signed-off-by: Hanna Czenczek Reviewed-by: Stefan Hajnoczi --- block/block-backend.c | 22 +++++++++++----------- 1 file changed, 11 insertions(+), 11 deletions(-) diff --git a/block/block-backend.c b/block/block-backend.c index 209eb07528..9c4de79e6b 100644 --- a/block/block-backend.c +++ b/block/block-backend.c @@ -44,7 +44,7 @@ struct BlockBackend { char *name; int refcnt; BdrvChild *root; - AioContext *ctx; + AioContext *ctx; /* access with atomic operations only */ DriveInfo *legacy_dinfo; /* null unless created by drive_new() */ QTAILQ_ENTRY(BlockBackend) link; /* for block_backends */ QTAILQ_ENTRY(BlockBackend) monitor_link; /* for monitor_block_backends= */ @@ -2414,22 +2414,22 @@ void blk_op_unblock_all(BlockBackend *blk, Error *r= eason) } } =20 +/** + * Return BB's current AioContext. Note that this context may change + * concurrently at any time, with one exception: If the BB has a root node + * attached, its context will only change through bdrv_try_change_aio_cont= ext(), + * which creates a drained section. Therefore, incrementing such a BB's + * in-flight counter will prevent its context from changing. + */ AioContext *blk_get_aio_context(BlockBackend *blk) { - BlockDriverState *bs; IO_CODE(); =20 if (!blk) { return qemu_get_aio_context(); } =20 - bs =3D blk_bs(blk); - if (bs) { - AioContext *ctx =3D bdrv_get_aio_context(blk_bs(blk)); - assert(ctx =3D=3D blk->ctx); - } - - return blk->ctx; + return qatomic_read(&blk->ctx); } =20 int blk_set_aio_context(BlockBackend *blk, AioContext *new_context, @@ -2442,7 +2442,7 @@ int blk_set_aio_context(BlockBackend *blk, AioContext= *new_context, GLOBAL_STATE_CODE(); =20 if (!bs) { - blk->ctx =3D new_context; + qatomic_set(&blk->ctx, new_context); return 0; } =20 @@ -2471,7 +2471,7 @@ static void blk_root_set_aio_ctx_commit(void *opaque) AioContext *new_context =3D s->new_ctx; ThrottleGroupMember *tgm =3D &blk->public.throttle_group_member; =20 - blk->ctx =3D new_context; + qatomic_set(&blk->ctx, new_context); if (tgm->throttle_state) { throttle_group_detach_aio_context(tgm); throttle_group_attach_aio_context(tgm, new_context); --=20 2.43.0 From nobody Tue Nov 26 13:31:14 2024 Delivered-To: importer@patchew.org Authentication-Results: mx.zohomail.com; dkim=pass; spf=pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org; dmarc=pass(p=none dis=none) header.from=redhat.com ARC-Seal: i=1; a=rsa-sha256; t=1706885341; cv=none; d=zohomail.com; s=zohoarc; b=EJOp4fpVo1Tflu+xzzI9E8CAu/SuUIDsPmPCHqLnqUit1E1t/VXO9N66GPhIvXotRFUdY5TNz32qscLxuPco5Tfm6DrJg9oi0K764ZvPpKYGiVLHJztEf8lg7OacE9WIwzu0LHc1qP1XYowI89HAontYMYp+OesCGOvBDMVMnD0= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=zohomail.com; s=zohoarc; t=1706885341; h=Content-Type:Content-Transfer-Encoding:Cc:Cc:Date:Date:From:From:In-Reply-To:List-Subscribe:List-Post:List-Id:List-Archive:List-Help:List-Unsubscribe:MIME-Version:Message-ID:References:Sender:Subject:Subject:To:To:Message-Id:Reply-To; bh=6akKXCXv6EsoFlkIsJ766ksyO2x05Vult6oh9xmylrY=; 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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