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M . Jones" , Ilya Dryomov , Peter Lieven , =?UTF-8?q?Philippe=20Mathieu-Daud=C3=A9?= , =?UTF-8?q?Alex=20Benn=C3=A9e?= , Fam Zheng , Ronnie Sahlberg Subject: [PATCH v2 03/19] =?UTF-8?q?iscsi:=20Run=20co=20BH=20CB=20in=20the?= =?UTF-8?q?=20coroutine=E2=80=99s=20AioContext?= Date: Mon, 10 Nov 2025 16:48:38 +0100 Message-ID: <20251110154854.151484-4-hreitz@redhat.com> X-Mailer: git-send-email 2.51.1 In-Reply-To: <20251110154854.151484-1-hreitz@redhat.com> References: <20251110154854.151484-1-hreitz@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable 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: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, 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, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 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: 1762789864452158500 For rbd (and others), as described in =E2=80=9Crbd: Run co BH CB in the coroutine=E2=80=99s AioContext=E2=80=9D, the pattern of setting a completio= n flag and waking a coroutine that yields while the flag is not set can only work when both run in the same thread. iscsi has the same pattern, but the details are a bit different: iscsi_co_generic_cb() can (as far as I understand) only run through iscsi_service(), not just from a random thread at a random time. iscsi_service() in turn can only be run after iscsi_set_events() set up an FD event handler, which is done in iscsi_co_wait_for_task(). As a result, iscsi_co_wait_for_task() will always yield exactly once, because iscsi_co_generic_cb() can only run after iscsi_set_events(), after the completion flag has already been checked, and the yielding coroutine will then be woken only once the completion flag was set to true. So as far as I can tell, iscsi has no bug and already works fine. Still, we don=E2=80=99t need the completion flag because we know we have to yield exactly once, so we can drop it. This simplifies the code and makes it more obvious that the =E2=80=9Crbd bug=E2=80=9D isn=E2=80=99t pres= ent here. This makes iscsi_co_generic_bh_cb() and iscsi_retry_timer_expired() a bit boring, so at least the former we can drop and call aio_co_wake() directly from scsi_co_generic_cb() to the same effect. As for the latter, the timer needs a CB, so we can=E2=80=99t drop it (I suppose we cou= ld technically use aio_co_wake directly as the CB, but that would be nasty), but we can put it into the coroutine=E2=80=99s AioContext to make i= ts aio_co_wake() a simple wrapper around qemu_coroutine_enter() without a further BH indirection. Finally, remove the iTask->co !=3D NULL checks: This field is set by iscsi_co_init_iscsitask(), which all users of IscsiTask run before even setting up iscsi_co_generic_cb() as the callback, and it is never set or cleared elsewhere, so it is impossible to not be set in iscsi_co_generic_cb(). Signed-off-by: Hanna Czenczek --- block/iscsi.c | 56 +++++++++++++++++++-------------------------------- 1 file changed, 21 insertions(+), 35 deletions(-) diff --git a/block/iscsi.c b/block/iscsi.c index 15b96ee880..852ecccf0d 100644 --- a/block/iscsi.c +++ b/block/iscsi.c @@ -107,7 +107,6 @@ typedef struct IscsiLun { =20 typedef struct IscsiTask { int status; - int complete; int retries; int do_retry; struct scsi_task *task; @@ -180,21 +179,10 @@ iscsi_schedule_bh(IscsiAIOCB *acb) =20 #endif =20 -static void iscsi_co_generic_bh_cb(void *opaque) -{ - struct IscsiTask *iTask =3D opaque; - - iTask->complete =3D 1; - aio_co_wake(iTask->co); -} - static void iscsi_retry_timer_expired(void *opaque) { struct IscsiTask *iTask =3D opaque; - iTask->complete =3D 1; - if (iTask->co) { - aio_co_wake(iTask->co); - } + aio_co_wake(iTask->co); } =20 static inline unsigned exp_random(double mean) @@ -239,6 +227,8 @@ iscsi_co_generic_cb(struct iscsi_context *iscsi, int st= atus, { struct IscsiTask *iTask =3D opaque; struct scsi_task *task =3D command_data; + IscsiLun *iscsilun =3D iTask->iscsilun; + AioContext *itask_ctx =3D qemu_coroutine_get_aio_context(iTask->co); =20 iTask->status =3D status; iTask->do_retry =3D 0; @@ -263,9 +253,9 @@ iscsi_co_generic_cb(struct iscsi_context *iscsi, int st= atus, " (retry #%u in %u ms): %s", iTask->retries, retry_time, iscsi_get_error(iscsi)); - aio_timer_init(iTask->iscsilun->aio_context, - &iTask->retry_timer, QEMU_CLOCK_REALTIME, - SCALE_MS, iscsi_retry_timer_expired, iTask); + aio_timer_init(itask_ctx, &iTask->retry_timer, + QEMU_CLOCK_REALTIME, SCALE_MS, + iscsi_retry_timer_expired, iTask); timer_mod(&iTask->retry_timer, qemu_clock_get_ms(QEMU_CLOCK_REALTIME) + retry_t= ime); iTask->do_retry =3D 1; @@ -284,12 +274,17 @@ iscsi_co_generic_cb(struct iscsi_context *iscsi, int = status, } } =20 - if (iTask->co) { - replay_bh_schedule_oneshot_event(iTask->iscsilun->aio_context, - iscsi_co_generic_bh_cb, iTask); - } else { - iTask->complete =3D 1; - } + /* + * aio_co_wake() is safe to call: iscsi_service(), which called us, is= only + * run from the event_timer and/or the FD handlers, never from the req= uest + * coroutine. The request coroutine in turn will yield unconditionall= y. + * We must release the lock, though, in case we enter the coroutine + * directly. (Note that if do we enter the coroutine, iTask will prob= ably + * be dangling once aio_co_wake() returns.) + */ + qemu_mutex_unlock(&iscsilun->mutex); + aio_co_wake(iTask->co); + qemu_mutex_lock(&iscsilun->mutex); } =20 static void coroutine_fn @@ -592,12 +587,10 @@ static inline bool iscsi_allocmap_is_valid(IscsiLun *= iscsilun, static void coroutine_fn iscsi_co_wait_for_task(IscsiTask *iTask, IscsiLun *iscsilun) { - while (!iTask->complete) { - iscsi_set_events(iscsilun); - qemu_mutex_unlock(&iscsilun->mutex); - qemu_coroutine_yield(); - qemu_mutex_lock(&iscsilun->mutex); - } + iscsi_set_events(iscsilun); + qemu_mutex_unlock(&iscsilun->mutex); + qemu_coroutine_yield(); + qemu_mutex_lock(&iscsilun->mutex); } =20 static int coroutine_fn @@ -669,7 +662,6 @@ retry: } =20 if (iTask.do_retry) { - iTask.complete =3D 0; goto retry; } =20 @@ -740,7 +732,6 @@ retry: scsi_free_scsi_task(iTask.task); iTask.task =3D NULL; } - iTask.complete =3D 0; goto retry; } =20 @@ -902,7 +893,6 @@ retry: } =20 if (iTask.do_retry) { - iTask.complete =3D 0; goto retry; } =20 @@ -940,7 +930,6 @@ retry: } =20 if (iTask.do_retry) { - iTask.complete =3D 0; goto retry; } =20 @@ -1184,7 +1173,6 @@ retry: } =20 if (iTask.do_retry) { - iTask.complete =3D 0; goto retry; } =20 @@ -1301,7 +1289,6 @@ retry: } =20 if (iTask.do_retry) { - iTask.complete =3D 0; goto retry; } =20 @@ -2390,7 +2377,6 @@ retry: iscsi_co_wait_for_task(&iscsi_task, dst_lun); =20 if (iscsi_task.do_retry) { - iscsi_task.complete =3D 0; goto retry; } =20 --=20 2.51.1