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Thu, 22 May 2025 12:05:55 +0000 (UTC) Received: from redhat.com (unknown [10.45.226.76]) by mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 31139195801F; Thu, 22 May 2025 12:05:49 +0000 (UTC) Date: Thu, 22 May 2025 14:05:47 +0200 From: Kevin Wolf To: Fiona Ebner Cc: qemu-block@nongnu.org, qemu-devel@nongnu.org, den@virtuozzo.com, andrey.drobyshev@virtuozzo.com, hreitz@redhat.com, stefanha@redhat.com, eblake@redhat.com, jsnow@redhat.com, vsementsov@yandex-team.ru, xiechanglong.d@gmail.com, wencongyang2@huawei.com, berto@igalia.com, fam@euphon.net, ari@tuxera.com Subject: Re: [PATCH v2 08/24] block: move drain outside of bdrv_change_aio_context() and mark GRAPH_RDLOCK Message-ID: References: <20250520103012.424311-1-f.ebner@proxmox.com> <20250520103012.424311-9-f.ebner@proxmox.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Scanned-By: MIMEDefang 3.0 on 10.30.177.40 Received-SPF: pass client-ip=170.10.129.124; envelope-from=kwolf@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -23 X-Spam_score: -2.4 X-Spam_bar: -- X-Spam_report: (-2.4 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.275, 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, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable 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+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Am 22.05.2025 um 11:09 hat Fiona Ebner geschrieben: > Am 21.05.25 um 18:05 schrieb Kevin Wolf: > > Am 20.05.2025 um 12:29 hat Fiona Ebner geschrieben: > >> This is in preparation to mark bdrv_drained_begin() as GRAPH_UNLOCKED. > >> > >> Note that even if bdrv_drained_begin() would already be marked as > > > > "if ... were already marked" > > Ack. > > ---snip 8<--- > > >> diff --git a/block.c b/block.c > >> index 01144c895e..7148618504 100644 > >> --- a/block.c > >> +++ b/block.c > >> @@ -106,9 +106,9 @@ static void bdrv_reopen_abort(BDRVReopenState *reopen_state); > >> > >> static bool bdrv_backing_overridden(BlockDriverState *bs); > >> > >> -static bool bdrv_change_aio_context(BlockDriverState *bs, AioContext *ctx, > >> - GHashTable *visited, Transaction *tran, > >> - Error **errp); > >> +static bool GRAPH_RDLOCK > >> +bdrv_change_aio_context(BlockDriverState *bs, AioContext *ctx, > >> + GHashTable *visited, Transaction *tran, Error **errp); > > > > For static functions, we should have rhe GRAPH_RDLOCK annotation both > > here and in the actual definition, too. > > Will fix in v3! > > >> /* If non-zero, use only whitelisted block drivers */ > >> static int use_bdrv_whitelist; > >> @@ -3040,8 +3040,10 @@ static void GRAPH_WRLOCK bdrv_attach_child_common_abort(void *opaque) > >> > >> /* No need to visit `child`, because it has been detached already */ > >> visited = g_hash_table_new(NULL, NULL); > >> + bdrv_drain_all_begin(); > >> ret = s->child->klass->change_aio_ctx(s->child, s->old_parent_ctx, > >> visited, tran, &error_abort); > >> + bdrv_drain_all_end(); > >> g_hash_table_destroy(visited); > >> > >> /* transaction is supposed to always succeed */ > >> @@ -3122,9 +3124,11 @@ bdrv_attach_child_common(BlockDriverState *child_bs, > >> bool ret_child; > >> > >> g_hash_table_add(visited, new_child); > >> + bdrv_drain_all_begin(); > >> ret_child = child_class->change_aio_ctx(new_child, child_ctx, > >> visited, aio_ctx_tran, > >> NULL); > >> + bdrv_drain_all_end(); > >> if (ret_child == true) { > >> error_free(local_err); > >> ret = 0; > > > > Should we document in the header file that BdrvChildClass.change_aio_ctx > > is called with the node drained? > > > > We could add assertions to bdrv_child/parent_change_aio_context or at > > least comments to this effect. (Assertions might be over the top because > > it's easy to verify that both are only called from > > bdrv_change_aio_context().) > > Sounds good. Would the following be okay? > > For bdrv_parent_change_aio_context() and for change_aio_ctx() the same > (except the name of @child is @c for the former): > > > /* > > * Changes the AioContext of for @child to @ctx and recursively for the > > * associated block nodes and all their children and parents. Returns true if "of for"? This might be a bit too specific for child_of_bds, while the function is also implemented for BlockBackends and block jobs. Keeping the description more in line with other BdrvChildClass functions, maybe something generic like: Notifies the parent that the child is trying to change its AioContext. The parent may in turn change the AioContext of other nodes in the same transaction. > > * the change is possible and the transaction @tran can be continued. Returns > > * false and sets @errp if not and the transaction must be aborted. > > * > > * @visited will accumulate all visited BdrvChild objects. The caller is > > * responsible for freeing the list afterwards. > > * > > * Must be called with the affected block nodes drained. > > */ > > and for bdrv_child_change_aio_context() slightly different: > > > /* > > * Changes the AioContext of for @c->bs to @ctx and recursively for all its Again "of for". > > * children and parents. Returns true if the change is possible and the > > * transaction @tran can be continued. Returns false and sets @errp if not and > > * the transaction must be aborted. > > * > > * @visited will accumulate all visited BdrvChild objects. The caller is > > * responsible for freeing the list afterwards. > > * > > * Must be called with the affected block nodes drained. > > */ The rest looks good. (Much better than what I would have done, I was only thinking of the last line without a proper documentation of the whole function.) Kevin