Re: [PATCH 1/2] srcu: Fix broken node geometry after early ssp init
On Mon, Apr 19, 2021 at 02:23:45AM +0200, Frederic Weisbecker wrote: > On Sat, Apr 17, 2021 at 09:46:16PM -0700, Paul E. McKenney wrote: > > On Sat, Apr 17, 2021 at 03:16:49PM +0200, Frederic Weisbecker wrote: > > > On Wed, Apr 14, 2021 at 08:55:38AM -0700, Paul E. McKenney wrote: > > > > > diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h > > > > > index 75ed367d5b60..24db97cbf76b 100644 > > > > > --- a/kernel/rcu/rcu.h > > > > > +++ b/kernel/rcu/rcu.h > > > > > @@ -278,6 +278,7 @@ extern void resched_cpu(int cpu); > > > > > extern int rcu_num_lvls; > > > > > extern int num_rcu_lvl[]; > > > > > extern int rcu_num_nodes; > > > > > +extern bool rcu_geometry_initialized; > > > > > > > > Can this be a static local variable inside rcu_init_geometry()? > > > > > > > > After all, init_srcu_struct() isn't called all that often, and its > > > > overhead > > > > is such that an extra function call and check is going to hurt it. This > > > > of course requires removing __init from rcu_init_geometry(), but it is > > > > not > > > > all that large, so why not just remove the __init? > > > > > > > > But if we really are worried about reclaiming rcu_init_geometry()'s > > > > instructions (maybe we are?), then rcu_init_geometry() can be split > > > > into a function that just does the check (which is not __init) and the > > > > remainder of the function, which could remain __init. > > > > > > There you go: > > > > Queued, thank you! > > Thanks! > > And please also consider "[PATCH 2/2] srcu: Early test SRCU polling start" > if you want to expand testing coverage to polling. Ah, thank you for the reminder! Queued and pushed. Thanx, Paul
Re: [PATCH 1/2] srcu: Fix broken node geometry after early ssp init
On Sat, Apr 17, 2021 at 09:46:16PM -0700, Paul E. McKenney wrote: > On Sat, Apr 17, 2021 at 03:16:49PM +0200, Frederic Weisbecker wrote: > > On Wed, Apr 14, 2021 at 08:55:38AM -0700, Paul E. McKenney wrote: > > > > diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h > > > > index 75ed367d5b60..24db97cbf76b 100644 > > > > --- a/kernel/rcu/rcu.h > > > > +++ b/kernel/rcu/rcu.h > > > > @@ -278,6 +278,7 @@ extern void resched_cpu(int cpu); > > > > extern int rcu_num_lvls; > > > > extern int num_rcu_lvl[]; > > > > extern int rcu_num_nodes; > > > > +extern bool rcu_geometry_initialized; > > > > > > Can this be a static local variable inside rcu_init_geometry()? > > > > > > After all, init_srcu_struct() isn't called all that often, and its > > > overhead > > > is such that an extra function call and check is going to hurt it. This > > > of course requires removing __init from rcu_init_geometry(), but it is not > > > all that large, so why not just remove the __init? > > > > > > But if we really are worried about reclaiming rcu_init_geometry()'s > > > instructions (maybe we are?), then rcu_init_geometry() can be split > > > into a function that just does the check (which is not __init) and the > > > remainder of the function, which could remain __init. > > > > There you go: > > Queued, thank you! Thanks! And please also consider "[PATCH 2/2] srcu: Early test SRCU polling start" if you want to expand testing coverage to polling.
Re: [PATCH 1/2] srcu: Fix broken node geometry after early ssp init
On Sat, Apr 17, 2021 at 03:16:49PM +0200, Frederic Weisbecker wrote: > On Wed, Apr 14, 2021 at 08:55:38AM -0700, Paul E. McKenney wrote: > > > diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h > > > index 75ed367d5b60..24db97cbf76b 100644 > > > --- a/kernel/rcu/rcu.h > > > +++ b/kernel/rcu/rcu.h > > > @@ -278,6 +278,7 @@ extern void resched_cpu(int cpu); > > > extern int rcu_num_lvls; > > > extern int num_rcu_lvl[]; > > > extern int rcu_num_nodes; > > > +extern bool rcu_geometry_initialized; > > > > Can this be a static local variable inside rcu_init_geometry()? > > > > After all, init_srcu_struct() isn't called all that often, and its overhead > > is such that an extra function call and check is going to hurt it. This > > of course requires removing __init from rcu_init_geometry(), but it is not > > all that large, so why not just remove the __init? > > > > But if we really are worried about reclaiming rcu_init_geometry()'s > > instructions (maybe we are?), then rcu_init_geometry() can be split > > into a function that just does the check (which is not __init) and the > > remainder of the function, which could remain __init. > > There you go: Queued, thank you! Thanx, Paul > --- > From: Frederic Weisbecker > Date: Wed, 31 Mar 2021 16:10:36 +0200 > Subject: [PATCH] srcu: Fix broken node geometry after early ssp init > > An ssp initialized before rcu_init_geometry() will have its snp hierarchy > based on CONFIG_NR_CPUS. > > Once rcu_init_geometry() is called, the nodes distribution is shrinked > and optimized toward meeting the actual possible number of CPUs detected > on boot. > > Later on, the ssp that was initialized before rcu_init_geometry() is > confused and sometimes refers to its initial CONFIG_NR_CPUS based node > hierarchy, sometimes to the new num_possible_cpus() based one instead. > For example each of its sdp->mynode remain backward and refer to the > early node leaves that may not exist anymore. On the other hand the > srcu_for_each_node_breadth_first() refers to the new node hierarchy. > > There are at least two bad possible outcomes to this: > > 1) a) A callback enqueued early on an sdp is recorded pending on > sdp->mynode->srcu_data_have_cbs in srcu_funnel_gp_start() with > sdp->mynode pointing to a deep leaf (say 3 levels). > >b) The grace period ends after rcu_init_geometry() which shrinks the > nodes level to a single one. srcu_gp_end() walks through the new > snp hierarchy without ever reaching the old leaves so the callback > is never executed. > >This is easily reproduced on an 8 CPUs machine with >CONFIG_NR_CPUS >= 32 and "rcupdate.rcu_self_test=1". The >srcu_barrier() after early tests verification never completes and >the boot hangs: > > [ 5413.141029] INFO: task swapper/0:1 blocked for more than 4915 > seconds. > [ 5413.147564] Not tainted 5.12.0-rc4+ #28 > [ 5413.151927] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" > disables this message. > [ 5413.159753] task:swapper/0 state:D stack:0 pid:1 ppid: > 0 flags:0x4000 > [ 5413.168099] Call Trace: > [ 5413.170555] __schedule+0x36c/0x930 > [ 5413.174057] ? wait_for_completion+0x88/0x110 > [ 5413.178423] schedule+0x46/0xf0 > [ 5413.181575] schedule_timeout+0x284/0x380 > [ 5413.185591] ? wait_for_completion+0x88/0x110 > [ 5413.189957] ? mark_held_locks+0x61/0x80 > [ 5413.193882] ? mark_held_locks+0x61/0x80 > [ 5413.197809] ? _raw_spin_unlock_irq+0x24/0x50 > [ 5413.202173] ? wait_for_completion+0x88/0x110 > [ 5413.206535] wait_for_completion+0xb4/0x110 > [ 5413.210724] ? srcu_torture_stats_print+0x110/0x110 > [ 5413.215610] srcu_barrier+0x187/0x200 > [ 5413.219277] ? rcu_tasks_verify_self_tests+0x50/0x50 > [ 5413.224244] ? rdinit_setup+0x2b/0x2b > [ 5413.227907] rcu_verify_early_boot_tests+0x2d/0x40 > [ 5413.232700] do_one_initcall+0x63/0x310 > [ 5413.236541] ? rdinit_setup+0x2b/0x2b > [ 5413.240207] ? rcu_read_lock_sched_held+0x52/0x80 > [ 5413.244912] kernel_init_freeable+0x253/0x28f > [ 5413.249273] ? rest_init+0x250/0x250 > [ 5413.252846] kernel_init+0xa/0x110 > [ 5413.256257] ret_from_fork+0x22/0x30 > > 2) An ssp that gets initialized before rcu_init_geometry() and used >afterward will always have stale rdp->mynode references, resulting in >callbacks to be missed in srcu_gp_end(), just like in the previous >scenario. > > Solve this with initializing nodes geometry whenever an struct srcu_state > happens to be initialized before rcu_init(). This way we make sure the > RCU nodes hierarchy is properly built and distributed before the nodes > of an struct srcu_state are allocated. > > Suggested-by: Paul E. McKenney > Signed-off-by: Frederic Weisbecker > Cc: Boqun Feng > Cc: Lai
Re: [PATCH 1/2] srcu: Fix broken node geometry after early ssp init
On Wed, Apr 14, 2021 at 08:55:38AM -0700, Paul E. McKenney wrote: > > diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h > > index 75ed367d5b60..24db97cbf76b 100644 > > --- a/kernel/rcu/rcu.h > > +++ b/kernel/rcu/rcu.h > > @@ -278,6 +278,7 @@ extern void resched_cpu(int cpu); > > extern int rcu_num_lvls; > > extern int num_rcu_lvl[]; > > extern int rcu_num_nodes; > > +extern bool rcu_geometry_initialized; > > Can this be a static local variable inside rcu_init_geometry()? > > After all, init_srcu_struct() isn't called all that often, and its overhead > is such that an extra function call and check is going to hurt it. This > of course requires removing __init from rcu_init_geometry(), but it is not > all that large, so why not just remove the __init? > > But if we really are worried about reclaiming rcu_init_geometry()'s > instructions (maybe we are?), then rcu_init_geometry() can be split > into a function that just does the check (which is not __init) and the > remainder of the function, which could remain __init. There you go: --- From: Frederic Weisbecker Date: Wed, 31 Mar 2021 16:10:36 +0200 Subject: [PATCH] srcu: Fix broken node geometry after early ssp init An ssp initialized before rcu_init_geometry() will have its snp hierarchy based on CONFIG_NR_CPUS. Once rcu_init_geometry() is called, the nodes distribution is shrinked and optimized toward meeting the actual possible number of CPUs detected on boot. Later on, the ssp that was initialized before rcu_init_geometry() is confused and sometimes refers to its initial CONFIG_NR_CPUS based node hierarchy, sometimes to the new num_possible_cpus() based one instead. For example each of its sdp->mynode remain backward and refer to the early node leaves that may not exist anymore. On the other hand the srcu_for_each_node_breadth_first() refers to the new node hierarchy. There are at least two bad possible outcomes to this: 1) a) A callback enqueued early on an sdp is recorded pending on sdp->mynode->srcu_data_have_cbs in srcu_funnel_gp_start() with sdp->mynode pointing to a deep leaf (say 3 levels). b) The grace period ends after rcu_init_geometry() which shrinks the nodes level to a single one. srcu_gp_end() walks through the new snp hierarchy without ever reaching the old leaves so the callback is never executed. This is easily reproduced on an 8 CPUs machine with CONFIG_NR_CPUS >= 32 and "rcupdate.rcu_self_test=1". The srcu_barrier() after early tests verification never completes and the boot hangs: [ 5413.141029] INFO: task swapper/0:1 blocked for more than 4915 seconds. [ 5413.147564] Not tainted 5.12.0-rc4+ #28 [ 5413.151927] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. [ 5413.159753] task:swapper/0 state:D stack:0 pid:1 ppid: 0 flags:0x4000 [ 5413.168099] Call Trace: [ 5413.170555] __schedule+0x36c/0x930 [ 5413.174057] ? wait_for_completion+0x88/0x110 [ 5413.178423] schedule+0x46/0xf0 [ 5413.181575] schedule_timeout+0x284/0x380 [ 5413.185591] ? wait_for_completion+0x88/0x110 [ 5413.189957] ? mark_held_locks+0x61/0x80 [ 5413.193882] ? mark_held_locks+0x61/0x80 [ 5413.197809] ? _raw_spin_unlock_irq+0x24/0x50 [ 5413.202173] ? wait_for_completion+0x88/0x110 [ 5413.206535] wait_for_completion+0xb4/0x110 [ 5413.210724] ? srcu_torture_stats_print+0x110/0x110 [ 5413.215610] srcu_barrier+0x187/0x200 [ 5413.219277] ? rcu_tasks_verify_self_tests+0x50/0x50 [ 5413.224244] ? rdinit_setup+0x2b/0x2b [ 5413.227907] rcu_verify_early_boot_tests+0x2d/0x40 [ 5413.232700] do_one_initcall+0x63/0x310 [ 5413.236541] ? rdinit_setup+0x2b/0x2b [ 5413.240207] ? rcu_read_lock_sched_held+0x52/0x80 [ 5413.244912] kernel_init_freeable+0x253/0x28f [ 5413.249273] ? rest_init+0x250/0x250 [ 5413.252846] kernel_init+0xa/0x110 [ 5413.256257] ret_from_fork+0x22/0x30 2) An ssp that gets initialized before rcu_init_geometry() and used afterward will always have stale rdp->mynode references, resulting in callbacks to be missed in srcu_gp_end(), just like in the previous scenario. Solve this with initializing nodes geometry whenever an struct srcu_state happens to be initialized before rcu_init(). This way we make sure the RCU nodes hierarchy is properly built and distributed before the nodes of an struct srcu_state are allocated. Suggested-by: Paul E. McKenney Signed-off-by: Frederic Weisbecker Cc: Boqun Feng Cc: Lai Jiangshan Cc: Neeraj Upadhyay Cc: Josh Triplett Cc: Joel Fernandes Cc: Uladzislau Rezki --- kernel/rcu/rcu.h | 2 ++ kernel/rcu/srcutree.c | 3 +++ kernel/rcu/tree.c | 17 - 3 files changed, 21 insertions(+), 1 deletion(-) diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h index
Re: [PATCH 1/2] srcu: Fix broken node geometry after early ssp init
On Wed, Apr 14, 2021 at 08:55:38AM -0700, Paul E. McKenney wrote:
> On Wed, Apr 14, 2021 at 03:24:12PM +0200, Frederic Weisbecker wrote:
> > diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
> > index 75ed367d5b60..24db97cbf76b 100644
> > --- a/kernel/rcu/rcu.h
> > +++ b/kernel/rcu/rcu.h
> > @@ -278,6 +278,7 @@ extern void resched_cpu(int cpu);
> > extern int rcu_num_lvls;
> > extern int num_rcu_lvl[];
> > extern int rcu_num_nodes;
> > +extern bool rcu_geometry_initialized;
>
> Can this be a static local variable inside rcu_init_geometry()?
>
> After all, init_srcu_struct() isn't called all that often, and its overhead
> is such that an extra function call and check is going to hurt it. This
> of course requires removing __init from rcu_init_geometry(), but it is not
> all that large, so why not just remove the __init?
>
> But if we really are worried about reclaiming rcu_init_geometry()'s
> instructions (maybe we are?), then rcu_init_geometry() can be split
> into a function that just does the check (which is not __init) and the
> remainder of the function, which could remain __init.
Indeed that makes sense, I'll move the variable inside rcu_init_geometry().
Also since rcu_init_geometry() can now be called anytime after the boot, I
already removed the __init. I don't think we can do the split trick because a
non-init function can't call an __init function. That would trigger a section
mismatch.
> > @@ -171,6 +171,8 @@ static int init_srcu_struct_fields(struct srcu_struct
> > *ssp, bool is_static)
> > ssp->sda = alloc_percpu(struct srcu_data);
> > if (!ssp->sda)
> > return -ENOMEM;
> > + if (!rcu_geometry_initialized)
> > + rcu_init_geometry();
>
> With the suggested change above, this just becomes an unconditional call
> to rcu_init_geometry().
Right.
> > -static void __init rcu_init_geometry(void)
> > +void rcu_init_geometry(void)
> > {
> > ulong d;
> > int i;
> > + static unsigned long old_nr_cpu_ids;
> > int rcu_capacity[RCU_NUM_LVLS];
>
> And then rcu_geometry_initialized is declared static here.
>
> Or am I missing something?
Looks good, I'll resend with that.
Thanks!
>
> > + if (rcu_geometry_initialized) {
> > + /*
> > +* Arrange for warning if rcu_init_geometry() was called before
> > +* setup_nr_cpu_ids(). We may miss cases when
> > +* nr_cpus_ids == NR_CPUS but that shouldn't matter too much.
> > +*/
> > + WARN_ON_ONCE(old_nr_cpu_ids != nr_cpu_ids);
> > + return;
> > + }
> > +
> > + old_nr_cpu_ids = nr_cpu_ids;
> > + rcu_geometry_initialized = true;
> > +
> > /*
> > * Initialize any unspecified boot parameters.
> > * The default values of jiffies_till_first_fqs and
> > --
> > 2.25.1
> >
Re: [PATCH 1/2] srcu: Fix broken node geometry after early ssp init
On Wed, Apr 14, 2021 at 03:24:12PM +0200, Frederic Weisbecker wrote: > An ssp initialized before rcu_init_geometry() will have its snp hierarchy > based on CONFIG_NR_CPUS. > > Once rcu_init_geometry() is called, the nodes distribution is shrinked > and optimized toward meeting the actual possible number of CPUs detected > on boot. > > Later on, the ssp that was initialized before rcu_init_geometry() is > confused and sometimes refers to its initial CONFIG_NR_CPUS based node > hierarchy, sometimes to the new num_possible_cpus() based one instead. > For example each of its sdp->mynode remain backward and refer to the > early node leaves that may not exist anymore. On the other hand the > srcu_for_each_node_breadth_first() refers to the new node hierarchy. > > There are at least two bad possible outcomes to this: > > 1) a) A callback enqueued early on an sdp is recorded pending on > sdp->mynode->srcu_data_have_cbs in srcu_funnel_gp_start() with > sdp->mynode pointing to a deep leaf (say 3 levels). > >b) The grace period ends after rcu_init_geometry() which shrinks the > nodes level to a single one. srcu_gp_end() walks through the new > snp hierarchy without ever reaching the old leaves so the callback > is never executed. > >This is easily reproduced on an 8 CPUs machine with >CONFIG_NR_CPUS >= 32 and "rcupdate.rcu_self_test=1". The >srcu_barrier() after early tests verification never completes and >the boot hangs: > > [ 5413.141029] INFO: task swapper/0:1 blocked for more than 4915 > seconds. > [ 5413.147564] Not tainted 5.12.0-rc4+ #28 > [ 5413.151927] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" > disables this message. > [ 5413.159753] task:swapper/0 state:D stack:0 pid:1 ppid: > 0 flags:0x4000 > [ 5413.168099] Call Trace: > [ 5413.170555] __schedule+0x36c/0x930 > [ 5413.174057] ? wait_for_completion+0x88/0x110 > [ 5413.178423] schedule+0x46/0xf0 > [ 5413.181575] schedule_timeout+0x284/0x380 > [ 5413.185591] ? wait_for_completion+0x88/0x110 > [ 5413.189957] ? mark_held_locks+0x61/0x80 > [ 5413.193882] ? mark_held_locks+0x61/0x80 > [ 5413.197809] ? _raw_spin_unlock_irq+0x24/0x50 > [ 5413.202173] ? wait_for_completion+0x88/0x110 > [ 5413.206535] wait_for_completion+0xb4/0x110 > [ 5413.210724] ? srcu_torture_stats_print+0x110/0x110 > [ 5413.215610] srcu_barrier+0x187/0x200 > [ 5413.219277] ? rcu_tasks_verify_self_tests+0x50/0x50 > [ 5413.224244] ? rdinit_setup+0x2b/0x2b > [ 5413.227907] rcu_verify_early_boot_tests+0x2d/0x40 > [ 5413.232700] do_one_initcall+0x63/0x310 > [ 5413.236541] ? rdinit_setup+0x2b/0x2b > [ 5413.240207] ? rcu_read_lock_sched_held+0x52/0x80 > [ 5413.244912] kernel_init_freeable+0x253/0x28f > [ 5413.249273] ? rest_init+0x250/0x250 > [ 5413.252846] kernel_init+0xa/0x110 > [ 5413.256257] ret_from_fork+0x22/0x30 > > 2) An ssp that gets initialized before rcu_init_geometry() and used >afterward will always have stale rdp->mynode references, resulting in >callbacks to be missed in srcu_gp_end(), just like in the previous >scenario. > > Solve this with calling rcu_init_geometry() whenever an struct srcu_state > happens to be initialized before rcu_init(). This way we make sure the > RCU nodes hierarchy is properly built and distributed before the nodes > of a struct srcu_state are allocated. > > Suggested-by: Paul E. McKenney > Signed-off-by: Frederic Weisbecker Much much nicer, thank you! Comments and questions interspersed. Thanx, Paul > Cc: Boqun Feng > Cc: Lai Jiangshan > Cc: Neeraj Upadhyay > Cc: Josh Triplett > Cc: Joel Fernandes > Cc: Uladzislau Rezki > --- > kernel/rcu/rcu.h | 3 +++ > kernel/rcu/srcutree.c | 2 ++ > kernel/rcu/tree.c | 18 +- > 3 files changed, 22 insertions(+), 1 deletion(-) > > diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h > index 75ed367d5b60..24db97cbf76b 100644 > --- a/kernel/rcu/rcu.h > +++ b/kernel/rcu/rcu.h > @@ -278,6 +278,7 @@ extern void resched_cpu(int cpu); > extern int rcu_num_lvls; > extern int num_rcu_lvl[]; > extern int rcu_num_nodes; > +extern bool rcu_geometry_initialized; Can this be a static local variable inside rcu_init_geometry()? After all, init_srcu_struct() isn't called all that often, and its overhead is such that an extra function call and check is going to hurt it. This of course requires removing __init from rcu_init_geometry(), but it is not all that large, so why not just remove the __init? But if we really are worried about reclaiming rcu_init_geometry()'s instructions (maybe we are?), then rcu_init_geometry() can be split into a function that just does the check (which is not __init) and the remainder of the function, which could remain
[PATCH 1/2] srcu: Fix broken node geometry after early ssp init
An ssp initialized before rcu_init_geometry() will have its snp hierarchy based on CONFIG_NR_CPUS. Once rcu_init_geometry() is called, the nodes distribution is shrinked and optimized toward meeting the actual possible number of CPUs detected on boot. Later on, the ssp that was initialized before rcu_init_geometry() is confused and sometimes refers to its initial CONFIG_NR_CPUS based node hierarchy, sometimes to the new num_possible_cpus() based one instead. For example each of its sdp->mynode remain backward and refer to the early node leaves that may not exist anymore. On the other hand the srcu_for_each_node_breadth_first() refers to the new node hierarchy. There are at least two bad possible outcomes to this: 1) a) A callback enqueued early on an sdp is recorded pending on sdp->mynode->srcu_data_have_cbs in srcu_funnel_gp_start() with sdp->mynode pointing to a deep leaf (say 3 levels). b) The grace period ends after rcu_init_geometry() which shrinks the nodes level to a single one. srcu_gp_end() walks through the new snp hierarchy without ever reaching the old leaves so the callback is never executed. This is easily reproduced on an 8 CPUs machine with CONFIG_NR_CPUS >= 32 and "rcupdate.rcu_self_test=1". The srcu_barrier() after early tests verification never completes and the boot hangs: [ 5413.141029] INFO: task swapper/0:1 blocked for more than 4915 seconds. [ 5413.147564] Not tainted 5.12.0-rc4+ #28 [ 5413.151927] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. [ 5413.159753] task:swapper/0 state:D stack:0 pid:1 ppid: 0 flags:0x4000 [ 5413.168099] Call Trace: [ 5413.170555] __schedule+0x36c/0x930 [ 5413.174057] ? wait_for_completion+0x88/0x110 [ 5413.178423] schedule+0x46/0xf0 [ 5413.181575] schedule_timeout+0x284/0x380 [ 5413.185591] ? wait_for_completion+0x88/0x110 [ 5413.189957] ? mark_held_locks+0x61/0x80 [ 5413.193882] ? mark_held_locks+0x61/0x80 [ 5413.197809] ? _raw_spin_unlock_irq+0x24/0x50 [ 5413.202173] ? wait_for_completion+0x88/0x110 [ 5413.206535] wait_for_completion+0xb4/0x110 [ 5413.210724] ? srcu_torture_stats_print+0x110/0x110 [ 5413.215610] srcu_barrier+0x187/0x200 [ 5413.219277] ? rcu_tasks_verify_self_tests+0x50/0x50 [ 5413.224244] ? rdinit_setup+0x2b/0x2b [ 5413.227907] rcu_verify_early_boot_tests+0x2d/0x40 [ 5413.232700] do_one_initcall+0x63/0x310 [ 5413.236541] ? rdinit_setup+0x2b/0x2b [ 5413.240207] ? rcu_read_lock_sched_held+0x52/0x80 [ 5413.244912] kernel_init_freeable+0x253/0x28f [ 5413.249273] ? rest_init+0x250/0x250 [ 5413.252846] kernel_init+0xa/0x110 [ 5413.256257] ret_from_fork+0x22/0x30 2) An ssp that gets initialized before rcu_init_geometry() and used afterward will always have stale rdp->mynode references, resulting in callbacks to be missed in srcu_gp_end(), just like in the previous scenario. Solve this with calling rcu_init_geometry() whenever an struct srcu_state happens to be initialized before rcu_init(). This way we make sure the RCU nodes hierarchy is properly built and distributed before the nodes of a struct srcu_state are allocated. Suggested-by: Paul E. McKenney Signed-off-by: Frederic Weisbecker Cc: Boqun Feng Cc: Lai Jiangshan Cc: Neeraj Upadhyay Cc: Josh Triplett Cc: Joel Fernandes Cc: Uladzislau Rezki --- kernel/rcu/rcu.h | 3 +++ kernel/rcu/srcutree.c | 2 ++ kernel/rcu/tree.c | 18 +- 3 files changed, 22 insertions(+), 1 deletion(-) diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h index 75ed367d5b60..24db97cbf76b 100644 --- a/kernel/rcu/rcu.h +++ b/kernel/rcu/rcu.h @@ -278,6 +278,7 @@ extern void resched_cpu(int cpu); extern int rcu_num_lvls; extern int num_rcu_lvl[]; extern int rcu_num_nodes; +extern bool rcu_geometry_initialized; static bool rcu_fanout_exact; static int rcu_fanout_leaf; @@ -308,6 +309,8 @@ static inline void rcu_init_levelspread(int *levelspread, const int *levelcnt) } } +extern void rcu_init_geometry(void); + /* Returns a pointer to the first leaf rcu_node structure. */ #define rcu_first_leaf_node() (rcu_state.level[rcu_num_lvls - 1]) diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c index 108f9ca06047..05ca3c275af1 100644 --- a/kernel/rcu/srcutree.c +++ b/kernel/rcu/srcutree.c @@ -171,6 +171,8 @@ static int init_srcu_struct_fields(struct srcu_struct *ssp, bool is_static) ssp->sda = alloc_percpu(struct srcu_data); if (!ssp->sda) return -ENOMEM; + if (!rcu_geometry_initialized) + rcu_init_geometry(); init_srcu_struct_nodes(ssp); ssp->srcu_gp_seq_needed_exp = 0; ssp->srcu_last_gp_end = ktime_get_mono_fast_ns(); diff --git
