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bh=fkE6zYHAZbMBHYcsuhPzvBy+Dqzg3JkSMxYsuqyZKK4=; b=OeohwOry78nxMlFk70zEGDetJDAsDRGoi60kS3vjd0a5MQhlqYq4IpFzYxR+RjoHXTikzF PyKEcrfnNxlYbu74dRFKaXS8rxDGSGCR3jJf7qUzYPu6+yQqu4QGIzBnD9K7NXmWGyJoyb lu4jR5q+Osdk6pfXBi9zLkLhc2HPN2g= X-MC-Unique: _l362FRPPNyot1k4SPOebA-1 From: Kevin Wolf To: qemu-block@nongnu.org Cc: kwolf@redhat.com, stefanha@redhat.com, qemu-devel@nongnu.org Subject: [PULL 14/33] dma-helpers: don't lock AioContext in dma_blk_cb() Date: Thu, 21 Dec 2023 22:23:19 +0100 Message-ID: <20231221212339.164439-15-kwolf@redhat.com> In-Reply-To: <20231221212339.164439-1-kwolf@redhat.com> References: <20231221212339.164439-1-kwolf@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.8 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=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=-0.061, 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_H4=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: 1703194115715100003 Content-Type: text/plain; charset="utf-8" From: Stefan Hajnoczi Commit abfcd2760b3e ("dma-helpers: prevent dma_blk_cb() vs dma_aio_cancel() race") acquired the AioContext lock inside dma_blk_cb() to avoid a race with scsi_device_purge_requests() running in the main loop thread. The SCSI code no longer calls dma_aio_cancel() from the main loop thread while I/O is running in the IOThread AioContext. Therefore it is no longer necessary to take this lock to protect DMAAIOCB fields. The ->cb() function also does not require the lock because blk_aio_*() and friends do not need the AioContext lock. Both hw/ide/core.c and hw/ide/macio.c also call dma_blk_io() but don't rely on it taking the AioContext lock, so this change is safe. Signed-off-by: Stefan Hajnoczi Reviewed-by: Eric Blake Reviewed-by: Kevin Wolf Message-ID: <20231204164259.1515217-5-stefanha@redhat.com> Signed-off-by: Kevin Wolf --- system/dma-helpers.c | 7 ++----- 1 file changed, 2 insertions(+), 5 deletions(-) diff --git a/system/dma-helpers.c b/system/dma-helpers.c index 36211acc7e..528117f256 100644 --- a/system/dma-helpers.c +++ b/system/dma-helpers.c @@ -119,13 +119,12 @@ static void dma_blk_cb(void *opaque, int ret) =20 trace_dma_blk_cb(dbs, ret); =20 - aio_context_acquire(ctx); dbs->acb =3D NULL; dbs->offset +=3D dbs->iov.size; =20 if (dbs->sg_cur_index =3D=3D dbs->sg->nsg || ret < 0) { dma_complete(dbs, ret); - goto out; + return; } dma_blk_unmap(dbs); =20 @@ -168,7 +167,7 @@ static void dma_blk_cb(void *opaque, int ret) trace_dma_map_wait(dbs); dbs->bh =3D aio_bh_new(ctx, reschedule_dma, dbs); cpu_register_map_client(dbs->bh); - goto out; + return; } =20 if (!QEMU_IS_ALIGNED(dbs->iov.size, dbs->align)) { @@ -179,8 +178,6 @@ static void dma_blk_cb(void *opaque, int ret) dbs->acb =3D dbs->io_func(dbs->offset, &dbs->iov, dma_blk_cb, dbs, dbs->io_func_opaque); assert(dbs->acb); -out: - aio_context_release(ctx); } =20 static void dma_aio_cancel(BlockAIOCB *acb) --=20 2.43.0