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bh=70hLchKKDMD2HpZFpzNZq73fWIcmHKXu1vjidAtQ9QA=; b=Ar0BblzNwQuDCg+Yiaup88aFtMovxRWCqvceauJTLbRHIMewfIelUo6oKRTGkLl8d9H2kY VDR3lXUI6WGRZaY9Yhyfawm6/AMG8BVgCh1DJve7g6kJW/NRKvphxicdNb5hDtHwspJbP1 tlF6NB1PMICYwf89kSBonmt9AMMk7ko= X-MC-Unique: ctUyZJtqPximIYwcBk0V_w-1 From: Kevin Wolf To: qemu-block@nongnu.org Cc: kwolf@redhat.com, hreitz@redhat.com, stefanha@redhat.com, qemu-devel@nongnu.org Subject: [PATCH for-8.2 1/4] block: Fix bdrv_graph_wrlock() call in blk_remove_bs() Date: Wed, 15 Nov 2023 18:20:09 +0100 Message-ID: <20231115172012.112727-2-kwolf@redhat.com> In-Reply-To: <20231115172012.112727-1-kwolf@redhat.com> References: <20231115172012.112727-1-kwolf@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=170.10.133.124; envelope-from=kwolf@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -21 X-Spam_score: -2.2 X-Spam_bar: -- X-Spam_report: (-2.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.099, 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_H3=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: 1700068912701100011 Content-Type: text/plain; charset="utf-8" While not all callers of blk_remove_bs() are correct in this respect, the assumption in the function is that callers hold the AioContext lock of the BlockBackend (this is required by the drain calls in it). In order to avoid deadlock in the nested event loop, bdrv_graph_wrlock() has then to be called with the root BlockDriverState as its parameter instead of NULL, so that this AioContext lock is temporarily dropped. Fixes: https://issues.redhat.com/browse/RHEL-1761 Signed-off-by: Kevin Wolf --- block/block-backend.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/block/block-backend.c b/block/block-backend.c index 4053134781..f6f05ead28 100644 --- a/block/block-backend.c +++ b/block/block-backend.c @@ -882,6 +882,8 @@ BlockBackend *blk_by_public(BlockBackendPublic *public) =20 /* * Disassociates the currently associated BlockDriverState from @blk. + * + * The caller must hold the AioContext lock for the BlockBackend. */ void blk_remove_bs(BlockBackend *blk) { @@ -916,7 +918,7 @@ void blk_remove_bs(BlockBackend *blk) root =3D blk->root; blk->root =3D NULL; =20 - bdrv_graph_wrlock(NULL); + bdrv_graph_wrlock(root->bs); bdrv_root_unref_child(root); bdrv_graph_wrunlock(); } --=20 2.41.0