* [PATCH] rcu/nocb: Clear rdp offloaded flags when rcuop/rcuog kthreads spawn failed @ 2022-02-28 9:36 Zqiang 2022-03-03 16:49 ` Frederic Weisbecker 0 siblings, 1 reply; 5+ messages in thread From: Zqiang @ 2022-02-28 9:36 UTC (permalink / raw) To: paulmck, frederic; +Cc: linux-kernel When CONFIG_RCU_NOCB_CPU is enabled and 'rcu_nocbs' is set, the rcuop and rcuog kthreads is created. however the rcuop or rcuog kthreads creation may fail, if failed, clear rdp offloaded flags. Signed-off-by: Zqiang <qiang1.zhang@intel.com> --- kernel/rcu/tree_nocb.h | 14 ++++++++++++-- 1 file changed, 12 insertions(+), 2 deletions(-) diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h index 46694e13398a..94b279147954 100644 --- a/kernel/rcu/tree_nocb.h +++ b/kernel/rcu/tree_nocb.h @@ -1246,7 +1246,7 @@ static void rcu_spawn_cpu_nocb_kthread(int cpu) "rcuog/%d", rdp_gp->cpu); if (WARN_ONCE(IS_ERR(t), "%s: Could not start rcuo GP kthread, OOM is now expected behavior\n", __func__)) { mutex_unlock(&rdp_gp->nocb_gp_kthread_mutex); - return; + goto end; } WRITE_ONCE(rdp_gp->nocb_gp_kthread, t); if (kthread_prio) @@ -1258,12 +1258,22 @@ static void rcu_spawn_cpu_nocb_kthread(int cpu) t = kthread_run(rcu_nocb_cb_kthread, rdp, "rcuo%c/%d", rcu_state.abbr, cpu); if (WARN_ONCE(IS_ERR(t), "%s: Could not start rcuo CB kthread, OOM is now expected behavior\n", __func__)) - return; + goto end; if (kthread_prio) sched_setscheduler_nocheck(t, SCHED_FIFO, &sp); WRITE_ONCE(rdp->nocb_cb_kthread, t); WRITE_ONCE(rdp->nocb_gp_kthread, rdp_gp->nocb_gp_kthread); + return; +end: + if (cpumask_test_cpu(cpu, rcu_nocb_mask)) { + rcu_segcblist_offload(&rdp->cblist, false); + rcu_segcblist_clear_flags(&rdp->cblist, + SEGCBLIST_KTHREAD_CB | SEGCBLIST_KTHREAD_GP); + rcu_segcblist_clear_flags(&rdp->cblist, SEGCBLIST_LOCKING); + rcu_segcblist_set_flags(&rdp->cblist, SEGCBLIST_RCU_CORE); + } + return; } /* How many CB CPU IDs per GP kthread? Default of -1 for sqrt(nr_cpu_ids). */ -- 2.25.1 ^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH] rcu/nocb: Clear rdp offloaded flags when rcuop/rcuog kthreads spawn failed 2022-02-28 9:36 [PATCH] rcu/nocb: Clear rdp offloaded flags when rcuop/rcuog kthreads spawn failed Zqiang @ 2022-03-03 16:49 ` Frederic Weisbecker 2022-03-08 7:37 ` Zhang, Qiang1 0 siblings, 1 reply; 5+ messages in thread From: Frederic Weisbecker @ 2022-03-03 16:49 UTC (permalink / raw) To: Zqiang; +Cc: paulmck, linux-kernel, Neeraj Upadhyay, Uladzislau Rezki, Boqun Feng On Mon, Feb 28, 2022 at 05:36:29PM +0800, Zqiang wrote: > When CONFIG_RCU_NOCB_CPU is enabled and 'rcu_nocbs' is set, the rcuop > and rcuog kthreads is created. however the rcuop or rcuog kthreads > creation may fail, if failed, clear rdp offloaded flags. > > Signed-off-by: Zqiang <qiang1.zhang@intel.com> > --- > kernel/rcu/tree_nocb.h | 14 ++++++++++++-- > 1 file changed, 12 insertions(+), 2 deletions(-) > > diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h > index 46694e13398a..94b279147954 100644 > --- a/kernel/rcu/tree_nocb.h > +++ b/kernel/rcu/tree_nocb.h > @@ -1246,7 +1246,7 @@ static void rcu_spawn_cpu_nocb_kthread(int cpu) > "rcuog/%d", rdp_gp->cpu); > if (WARN_ONCE(IS_ERR(t), "%s: Could not start rcuo GP kthread, OOM is now expected behavior\n", __func__)) { > mutex_unlock(&rdp_gp->nocb_gp_kthread_mutex); > - return; > + goto end; > } > WRITE_ONCE(rdp_gp->nocb_gp_kthread, t); > if (kthread_prio) > @@ -1258,12 +1258,22 @@ static void rcu_spawn_cpu_nocb_kthread(int cpu) > t = kthread_run(rcu_nocb_cb_kthread, rdp, > "rcuo%c/%d", rcu_state.abbr, cpu); > if (WARN_ONCE(IS_ERR(t), "%s: Could not start rcuo CB kthread, OOM is now expected behavior\n", __func__)) > - return; > + goto end; > > if (kthread_prio) > sched_setscheduler_nocheck(t, SCHED_FIFO, &sp); > WRITE_ONCE(rdp->nocb_cb_kthread, t); > WRITE_ONCE(rdp->nocb_gp_kthread, rdp_gp->nocb_gp_kthread); > + return; > +end: > + if (cpumask_test_cpu(cpu, rcu_nocb_mask)) { > + rcu_segcblist_offload(&rdp->cblist, false); > + rcu_segcblist_clear_flags(&rdp->cblist, > + SEGCBLIST_KTHREAD_CB | SEGCBLIST_KTHREAD_GP); > + rcu_segcblist_clear_flags(&rdp->cblist, SEGCBLIST_LOCKING); > + rcu_segcblist_set_flags(&rdp->cblist, SEGCBLIST_RCU_CORE); > + } Thanks you, consequences are indeed bad otherwise because the target is considered offloaded but nothing actually handles the callbacks. A few issues though: * The rdp_gp kthread may be running concurrently. If it's iterating this rdp and the SEGCBLIST_LOCKING flag is cleared in the middle, rcu_nocb_unlock() won't release (among many other possible issues). * we should clear the cpu from rcu_nocb_mask or we won't be able to later re-offload it. * we should then delete the rdp from the group list: list_del_rcu(&rdp->nocb_entry_rdp); So ideally we should call rcu_nocb_rdp_deoffload(). But then bear in mind: 1) We must lock rcu_state.barrier_mutex and hotplug read lock. But since we are calling rcutree_prepare_cpu(), we maybe holding hotplug write lock already. Therefore we first need to invert the locking dependency order between rcu_state.barrier_mutex and hotplug lock and then just lock the barrier_mutex before calling rcu_nocb_rdp_deoffload() from our failure path. 2) On rcu_nocb_rdp_deoffload(), handle non-existing nocb_gp and/or nocb_cb kthreads. Make sure we are holding nocb_gp_kthread_mutex. I'm going to take your patch and adapt it along those lines. Thanks! ^ permalink raw reply [flat|nested] 5+ messages in thread
* RE: [PATCH] rcu/nocb: Clear rdp offloaded flags when rcuop/rcuog kthreads spawn failed 2022-03-03 16:49 ` Frederic Weisbecker @ 2022-03-08 7:37 ` Zhang, Qiang1 2022-03-09 21:06 ` Frederic Weisbecker 0 siblings, 1 reply; 5+ messages in thread From: Zhang, Qiang1 @ 2022-03-08 7:37 UTC (permalink / raw) To: Frederic Weisbecker Cc: paulmck@kernel.org, linux-kernel@vger.kernel.org, Neeraj Upadhyay, Uladzislau Rezki, Boqun Feng On Mon, Feb 28, 2022 at 05:36:29PM +0800, Zqiang wrote: > When CONFIG_RCU_NOCB_CPU is enabled and 'rcu_nocbs' is set, the rcuop > and rcuog kthreads is created. however the rcuop or rcuog kthreads > creation may fail, if failed, clear rdp offloaded flags. > > Signed-off-by: Zqiang <qiang1.zhang@intel.com> > --- > kernel/rcu/tree_nocb.h | 14 ++++++++++++-- > 1 file changed, 12 insertions(+), 2 deletions(-) > > diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h index > 46694e13398a..94b279147954 100644 > --- a/kernel/rcu/tree_nocb.h > +++ b/kernel/rcu/tree_nocb.h > @@ -1246,7 +1246,7 @@ static void rcu_spawn_cpu_nocb_kthread(int cpu) > "rcuog/%d", rdp_gp->cpu); > if (WARN_ONCE(IS_ERR(t), "%s: Could not start rcuo GP kthread, OOM is now expected behavior\n", __func__)) { > mutex_unlock(&rdp_gp->nocb_gp_kthread_mutex); > - return; > + goto end; > } > WRITE_ONCE(rdp_gp->nocb_gp_kthread, t); > if (kthread_prio) > @@ -1258,12 +1258,22 @@ static void rcu_spawn_cpu_nocb_kthread(int cpu) > t = kthread_run(rcu_nocb_cb_kthread, rdp, > "rcuo%c/%d", rcu_state.abbr, cpu); > if (WARN_ONCE(IS_ERR(t), "%s: Could not start rcuo CB kthread, OOM is now expected behavior\n", __func__)) > - return; > + goto end; > > if (kthread_prio) > sched_setscheduler_nocheck(t, SCHED_FIFO, &sp); > WRITE_ONCE(rdp->nocb_cb_kthread, t); > WRITE_ONCE(rdp->nocb_gp_kthread, rdp_gp->nocb_gp_kthread); > + return; > +end: > + if (cpumask_test_cpu(cpu, rcu_nocb_mask)) { > + rcu_segcblist_offload(&rdp->cblist, false); > + rcu_segcblist_clear_flags(&rdp->cblist, > + SEGCBLIST_KTHREAD_CB | SEGCBLIST_KTHREAD_GP); > + rcu_segcblist_clear_flags(&rdp->cblist, SEGCBLIST_LOCKING); > + rcu_segcblist_set_flags(&rdp->cblist, SEGCBLIST_RCU_CORE); > + } >> >>Thanks you, consequences are indeed bad otherwise because the target is considered offloaded but nothing actually handles the callbacks. >> >>A few issues though: >> >>* The rdp_gp kthread may be running concurrently. If it's iterating this rdp and >> the SEGCBLIST_LOCKING flag is cleared in the middle, rcu_nocb_unlock() won't >> release (among many other possible issues). >> >>* we should clear the cpu from rcu_nocb_mask or we won't be able to later >> re-offload it. >> >>* we should then delete the rdp from the group list: >> >> list_del_rcu(&rdp->nocb_entry_rdp); >> >>So ideally we should call rcu_nocb_rdp_deoffload(). But then bear in mind: >> >>1) We must lock rcu_state.barrier_mutex and hotplug read lock. But since we >> are calling rcutree_prepare_cpu(), we maybe holding hotplug write lock >> already. >> >> Therefore we first need to invert the locking dependency order between >> rcu_state.barrier_mutex and hotplug lock and then just lock the barrier_mutex >> before calling rcu_nocb_rdp_deoffload() from our failure path. >> >> >>2) On rcu_nocb_rdp_deoffload(), handle non-existing nocb_gp and/or nocb_cb >> kthreads. Make sure we are holding nocb_gp_kthread_mutex. Sorry for my late reply, Is the nocb_gp_kthread_mutex really necessary? Because the cpu online/offline is serial operation, It is protected by cpus_write_lock() Thanks Zqiang >> >>I'm going to take your patch and adapt it along those lines. >> >>Thanks! ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] rcu/nocb: Clear rdp offloaded flags when rcuop/rcuog kthreads spawn failed 2022-03-08 7:37 ` Zhang, Qiang1 @ 2022-03-09 21:06 ` Frederic Weisbecker 2022-03-10 2:37 ` Zhang, Qiang1 0 siblings, 1 reply; 5+ messages in thread From: Frederic Weisbecker @ 2022-03-09 21:06 UTC (permalink / raw) To: Zhang, Qiang1 Cc: paulmck@kernel.org, linux-kernel@vger.kernel.org, Neeraj Upadhyay, Uladzislau Rezki, Boqun Feng On Tue, Mar 08, 2022 at 07:37:24AM +0000, Zhang, Qiang1 wrote: > > On Mon, Feb 28, 2022 at 05:36:29PM +0800, Zqiang wrote: > > When CONFIG_RCU_NOCB_CPU is enabled and 'rcu_nocbs' is set, the rcuop > > and rcuog kthreads is created. however the rcuop or rcuog kthreads > > creation may fail, if failed, clear rdp offloaded flags. > > > > Signed-off-by: Zqiang <qiang1.zhang@intel.com> > > --- > > kernel/rcu/tree_nocb.h | 14 ++++++++++++-- > > 1 file changed, 12 insertions(+), 2 deletions(-) > > > > diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h index > > 46694e13398a..94b279147954 100644 > > --- a/kernel/rcu/tree_nocb.h > > +++ b/kernel/rcu/tree_nocb.h > > @@ -1246,7 +1246,7 @@ static void rcu_spawn_cpu_nocb_kthread(int cpu) > > "rcuog/%d", rdp_gp->cpu); > > if (WARN_ONCE(IS_ERR(t), "%s: Could not start rcuo GP kthread, OOM is now expected behavior\n", __func__)) { > > mutex_unlock(&rdp_gp->nocb_gp_kthread_mutex); > > - return; > > + goto end; > > } > > WRITE_ONCE(rdp_gp->nocb_gp_kthread, t); > > if (kthread_prio) > > @@ -1258,12 +1258,22 @@ static void rcu_spawn_cpu_nocb_kthread(int cpu) > > t = kthread_run(rcu_nocb_cb_kthread, rdp, > > "rcuo%c/%d", rcu_state.abbr, cpu); > > if (WARN_ONCE(IS_ERR(t), "%s: Could not start rcuo CB kthread, OOM is now expected behavior\n", __func__)) > > - return; > > + goto end; > > > > if (kthread_prio) > > sched_setscheduler_nocheck(t, SCHED_FIFO, &sp); > > WRITE_ONCE(rdp->nocb_cb_kthread, t); > > WRITE_ONCE(rdp->nocb_gp_kthread, rdp_gp->nocb_gp_kthread); > > + return; > > +end: > > + if (cpumask_test_cpu(cpu, rcu_nocb_mask)) { > > + rcu_segcblist_offload(&rdp->cblist, false); > > + rcu_segcblist_clear_flags(&rdp->cblist, > > + SEGCBLIST_KTHREAD_CB | SEGCBLIST_KTHREAD_GP); > > + rcu_segcblist_clear_flags(&rdp->cblist, SEGCBLIST_LOCKING); > > + rcu_segcblist_set_flags(&rdp->cblist, SEGCBLIST_RCU_CORE); > > + } > >> > >>Thanks you, consequences are indeed bad otherwise because the target is considered offloaded but nothing actually handles the callbacks. > >> > >>A few issues though: > >> > >>* The rdp_gp kthread may be running concurrently. If it's iterating this rdp and > >> the SEGCBLIST_LOCKING flag is cleared in the middle, rcu_nocb_unlock() won't > >> release (among many other possible issues). > >> > >>* we should clear the cpu from rcu_nocb_mask or we won't be able to later > >> re-offload it. > >> > >>* we should then delete the rdp from the group list: > >> > >> list_del_rcu(&rdp->nocb_entry_rdp); > >> > >>So ideally we should call rcu_nocb_rdp_deoffload(). But then bear in mind: > >> > >>1) We must lock rcu_state.barrier_mutex and hotplug read lock. But since we > >> are calling rcutree_prepare_cpu(), we maybe holding hotplug write lock > >> already. > >> > >> Therefore we first need to invert the locking dependency order between > >> rcu_state.barrier_mutex and hotplug lock and then just lock the barrier_mutex > >> before calling rcu_nocb_rdp_deoffload() from our failure path. > >> > >> > >>2) On rcu_nocb_rdp_deoffload(), handle non-existing nocb_gp and/or nocb_cb > >> kthreads. Make sure we are holding nocb_gp_kthread_mutex. > > Sorry for my late reply, Is the nocb_gp_kthread_mutex really necessary? > Because the cpu online/offline is serial operation, It is protected by cpus_write_lock() And you're right! But some people are working on making cpu_up() able to work in parallel for faster bring-up on boot. ^ permalink raw reply [flat|nested] 5+ messages in thread
* RE: [PATCH] rcu/nocb: Clear rdp offloaded flags when rcuop/rcuog kthreads spawn failed 2022-03-09 21:06 ` Frederic Weisbecker @ 2022-03-10 2:37 ` Zhang, Qiang1 0 siblings, 0 replies; 5+ messages in thread From: Zhang, Qiang1 @ 2022-03-10 2:37 UTC (permalink / raw) To: Frederic Weisbecker Cc: paulmck@kernel.org, linux-kernel@vger.kernel.org, Neeraj Upadhyay, Uladzislau Rezki, Boqun Feng On Tue, Mar 08, 2022 at 07:37:24AM +0000, Zhang, Qiang1 wrote: > > On Mon, Feb 28, 2022 at 05:36:29PM +0800, Zqiang wrote: > > When CONFIG_RCU_NOCB_CPU is enabled and 'rcu_nocbs' is set, the > > rcuop and rcuog kthreads is created. however the rcuop or rcuog > > kthreads creation may fail, if failed, clear rdp offloaded flags. > > > > Signed-off-by: Zqiang <qiang1.zhang@intel.com> > > --- > > kernel/rcu/tree_nocb.h | 14 ++++++++++++-- > > 1 file changed, 12 insertions(+), 2 deletions(-) > > > > diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h index > > 46694e13398a..94b279147954 100644 > > --- a/kernel/rcu/tree_nocb.h > > +++ b/kernel/rcu/tree_nocb.h > > @@ -1246,7 +1246,7 @@ static void rcu_spawn_cpu_nocb_kthread(int cpu) > > "rcuog/%d", rdp_gp->cpu); > > if (WARN_ONCE(IS_ERR(t), "%s: Could not start rcuo GP kthread, OOM is now expected behavior\n", __func__)) { > > mutex_unlock(&rdp_gp->nocb_gp_kthread_mutex); > > - return; > > + goto end; > > } > > WRITE_ONCE(rdp_gp->nocb_gp_kthread, t); > > if (kthread_prio) > > @@ -1258,12 +1258,22 @@ static void rcu_spawn_cpu_nocb_kthread(int cpu) > > t = kthread_run(rcu_nocb_cb_kthread, rdp, > > "rcuo%c/%d", rcu_state.abbr, cpu); > > if (WARN_ONCE(IS_ERR(t), "%s: Could not start rcuo CB kthread, OOM is now expected behavior\n", __func__)) > > - return; > > + goto end; > > > > if (kthread_prio) > > sched_setscheduler_nocheck(t, SCHED_FIFO, &sp); > > WRITE_ONCE(rdp->nocb_cb_kthread, t); > > WRITE_ONCE(rdp->nocb_gp_kthread, rdp_gp->nocb_gp_kthread); > > + return; > > +end: > > + if (cpumask_test_cpu(cpu, rcu_nocb_mask)) { > > + rcu_segcblist_offload(&rdp->cblist, false); > > + rcu_segcblist_clear_flags(&rdp->cblist, > > + SEGCBLIST_KTHREAD_CB | SEGCBLIST_KTHREAD_GP); > > + rcu_segcblist_clear_flags(&rdp->cblist, SEGCBLIST_LOCKING); > > + rcu_segcblist_set_flags(&rdp->cblist, SEGCBLIST_RCU_CORE); > > + } > >> > >>Thanks you, consequences are indeed bad otherwise because the target is considered offloaded but nothing actually handles the callbacks. > >> > >>A few issues though: > >> > >>* The rdp_gp kthread may be running concurrently. If it's iterating > >>this rdp and > >> the SEGCBLIST_LOCKING flag is cleared in the middle, > >>rcu_nocb_unlock() won't > >> release (among many other possible issues). > >> > >>* we should clear the cpu from rcu_nocb_mask or we won't be able to > >>later > >> re-offload it. > >> > >>* we should then delete the rdp from the group list: > >> > >> list_del_rcu(&rdp->nocb_entry_rdp); > >> > >>So ideally we should call rcu_nocb_rdp_deoffload(). But then bear in mind: > >> > >>1) We must lock rcu_state.barrier_mutex and hotplug read lock. But since we > >> are calling rcutree_prepare_cpu(), we maybe holding hotplug write lock > >> already. > >> > >> Therefore we first need to invert the locking dependency order between > >> rcu_state.barrier_mutex and hotplug lock and then just lock the barrier_mutex > >> before calling rcu_nocb_rdp_deoffload() from our failure path. > >> > >> > >>2) On rcu_nocb_rdp_deoffload(), handle non-existing nocb_gp and/or nocb_cb > >> kthreads. Make sure we are holding nocb_gp_kthread_mutex. > > Sorry for my late reply, Is the nocb_gp_kthread_mutex really necessary? > Because the cpu online/offline is serial operation, It is protected > by cpus_write_lock() > >And you're right! But some people are working on making cpu_up() able to work in parallel for faster bring-up on boot. Thank you for explanation. Are you making the above changes to this patch? Thanks Zqiang ^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2022-03-10 2:37 UTC | newest] Thread overview: 5+ messages (download: mbox.gz follow: Atom feed -- links below jump to the message on this page -- 2022-02-28 9:36 [PATCH] rcu/nocb: Clear rdp offloaded flags when rcuop/rcuog kthreads spawn failed Zqiang 2022-03-03 16:49 ` Frederic Weisbecker 2022-03-08 7:37 ` Zhang, Qiang1 2022-03-09 21:06 ` Frederic Weisbecker 2022-03-10 2:37 ` Zhang, Qiang1
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