| Message ID | 20240201014100.3204532-6-boqun.feng@gmail.com (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | 0e8fbf319f1fd39e8250859e0228fc10b3861bb3 |
| Headers | show |
| Series | RCU nocb updates for v6.9 | expand |
Hello. On čtvrtek 1. února 2024 2:40:57 CET Boqun Feng wrote: > From: Zqiang <qiang.zhang1211@gmail.com> > > For the kernels built with CONFIG_RCU_NOCB_CPU_DEFAULT_ALL=y and > CONFIG_RCU_LAZY=y, the following scenarios will trigger WARN_ON_ONCE() > in the rcu_nocb_bypass_lock() and rcu_nocb_wait_contended() functions: > > CPU2 CPU11 > kthread > rcu_nocb_cb_kthread ksys_write > rcu_do_batch vfs_write > rcu_torture_timer_cb proc_sys_write > __kmem_cache_free proc_sys_call_handler > kmemleak_free drop_caches_sysctl_handler > delete_object_full drop_slab > __delete_object shrink_slab > put_object lazy_rcu_shrink_scan > call_rcu rcu_nocb_flush_bypass > __call_rcu_commn rcu_nocb_bypass_lock > raw_spin_trylock(&rdp->nocb_bypass_lock) fail > atomic_inc(&rdp->nocb_lock_contended); > rcu_nocb_wait_contended WARN_ON_ONCE(smp_processor_id() != rdp->cpu); > WARN_ON_ONCE(atomic_read(&rdp->nocb_lock_contended)) | > |_ _ _ _ _ _ _ _ _ _same rdp and rdp->cpu != 11_ _ _ _ _ _ _ _ _ __| > > Reproduce this bug with "echo 3 > /proc/sys/vm/drop_caches". > > This commit therefore uses rcu_nocb_try_flush_bypass() instead of > rcu_nocb_flush_bypass() in lazy_rcu_shrink_scan(). If the nocb_bypass > queue is being flushed, then rcu_nocb_try_flush_bypass will return > directly. > > Signed-off-by: Zqiang <qiang.zhang1211@gmail.com> > Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org> > Reviewed-by: Frederic Weisbecker <frederic@kernel.org> > Reviewed-by: Paul E. McKenney <paulmck@kernel.org> > Signed-off-by: Boqun Feng <boqun.feng@gmail.com> > --- > kernel/rcu/tree_nocb.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h > index 9e8052ba14b9..ffa69a5e18f4 100644 > --- a/kernel/rcu/tree_nocb.h > +++ b/kernel/rcu/tree_nocb.h > @@ -1391,7 +1391,7 @@ lazy_rcu_shrink_scan(struct shrinker *shrink, struct shrink_control *sc) > rcu_nocb_unlock_irqrestore(rdp, flags); > continue; > } > - WARN_ON_ONCE(!rcu_nocb_flush_bypass(rdp, NULL, jiffies, false)); > + rcu_nocb_try_flush_bypass(rdp, jiffies); > rcu_nocb_unlock_irqrestore(rdp, flags); > wake_nocb_gp(rdp, false); > sc->nr_to_scan -= _count; > Does this fix [1] [2]? Thank you. [1] https://bugzilla.kernel.org/show_bug.cgi?id=217948 [2] https://lore.kernel.org/lkml/8461340f-c7c8-4e1e-b7fa-a0e4b9a6c2a8@gmail.com/
On Sat, Feb 24, 2024 at 05:30:29PM +0100, Oleksandr Natalenko wrote: > Hello. > > On čtvrtek 1. února 2024 2:40:57 CET Boqun Feng wrote: > > From: Zqiang <qiang.zhang1211@gmail.com> > > > > For the kernels built with CONFIG_RCU_NOCB_CPU_DEFAULT_ALL=y and > > CONFIG_RCU_LAZY=y, the following scenarios will trigger WARN_ON_ONCE() > > in the rcu_nocb_bypass_lock() and rcu_nocb_wait_contended() functions: > > > > CPU2 CPU11 > > kthread > > rcu_nocb_cb_kthread ksys_write > > rcu_do_batch vfs_write > > rcu_torture_timer_cb proc_sys_write > > __kmem_cache_free proc_sys_call_handler > > kmemleak_free drop_caches_sysctl_handler > > delete_object_full drop_slab > > __delete_object shrink_slab > > put_object lazy_rcu_shrink_scan > > call_rcu rcu_nocb_flush_bypass > > __call_rcu_commn rcu_nocb_bypass_lock > > raw_spin_trylock(&rdp->nocb_bypass_lock) fail > > atomic_inc(&rdp->nocb_lock_contended); > > rcu_nocb_wait_contended WARN_ON_ONCE(smp_processor_id() != rdp->cpu); > > WARN_ON_ONCE(atomic_read(&rdp->nocb_lock_contended)) | > > |_ _ _ _ _ _ _ _ _ _same rdp and rdp->cpu != 11_ _ _ _ _ _ _ _ _ __| > > > > Reproduce this bug with "echo 3 > /proc/sys/vm/drop_caches". > > > > This commit therefore uses rcu_nocb_try_flush_bypass() instead of > > rcu_nocb_flush_bypass() in lazy_rcu_shrink_scan(). If the nocb_bypass > > queue is being flushed, then rcu_nocb_try_flush_bypass will return > > directly. > > > > Signed-off-by: Zqiang <qiang.zhang1211@gmail.com> > > Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org> > > Reviewed-by: Frederic Weisbecker <frederic@kernel.org> > > Reviewed-by: Paul E. McKenney <paulmck@kernel.org> > > Signed-off-by: Boqun Feng <boqun.feng@gmail.com> > > --- > > kernel/rcu/tree_nocb.h | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h > > index 9e8052ba14b9..ffa69a5e18f4 100644 > > --- a/kernel/rcu/tree_nocb.h > > +++ b/kernel/rcu/tree_nocb.h > > @@ -1391,7 +1391,7 @@ lazy_rcu_shrink_scan(struct shrinker *shrink, struct shrink_control *sc) > > rcu_nocb_unlock_irqrestore(rdp, flags); > > continue; > > } > > - WARN_ON_ONCE(!rcu_nocb_flush_bypass(rdp, NULL, jiffies, false)); > > + rcu_nocb_try_flush_bypass(rdp, jiffies); > > rcu_nocb_unlock_irqrestore(rdp, flags); > > wake_nocb_gp(rdp, false); > > sc->nr_to_scan -= _count; > > > > Does this fix [1] [2]? > > Thank you. > > [1] https://bugzilla.kernel.org/show_bug.cgi?id=217948 > [2] https://lore.kernel.org/lkml/8461340f-c7c8-4e1e-b7fa-a0e4b9a6c2a8@gmail.com/ It might, but why not apply it to the exact kernel version on which the bug appeared and see if it prevents it? Thanx, Paul
diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h index 9e8052ba14b9..ffa69a5e18f4 100644 --- a/kernel/rcu/tree_nocb.h +++ b/kernel/rcu/tree_nocb.h @@ -1391,7 +1391,7 @@ lazy_rcu_shrink_scan(struct shrinker *shrink, struct shrink_control *sc) rcu_nocb_unlock_irqrestore(rdp, flags); continue; } - WARN_ON_ONCE(!rcu_nocb_flush_bypass(rdp, NULL, jiffies, false)); + rcu_nocb_try_flush_bypass(rdp, jiffies); rcu_nocb_unlock_irqrestore(rdp, flags); wake_nocb_gp(rdp, false); sc->nr_to_scan -= _count;