* [Qemu-devel] possible ahci/migrate fix
@ 2019-02-27 12:10 Dr. David Alan Gilbert
2019-02-27 12:41 ` Juan Quintela
` (2 more replies)
0 siblings, 3 replies; 6+ messages in thread
From: Dr. David Alan Gilbert @ 2019-02-27 12:10 UTC (permalink / raw)
To: alex.bennee; +Cc: qemu-devel, quintela, peterx
Hi Alex,
Can you see if the attached patch fixes the ahci/migrate failure you
see; it won't fail for me however mean I am to it.
From f4c327d14d656d1c0f0e694d0efc6165493416f0 Mon Sep 17 00:00:00 2001
From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Date: Wed, 27 Feb 2019 12:04:37 +0000
Subject: [PATCH] migration: Cleanup during exit
Currently we cleanup the migration object as we exit main after the
main_loop finishes; however if there's a migration running things
get messy and we can end up with the migration thread still trying
to access freed structures.
We now take a ref to the object around the migration thread itself,
so the act of dropping the ref during exit doesn't cause us to lose
the state until the thread quits.
Cancelling the migration during migration also tries to get the thread
to quit.
We do this a bit earlier; so hopefully migration gets out of the way
before all the devices etc are freed.
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
---
migration/migration.c | 8 ++++++++
vl.c | 7 ++++++-
2 files changed, 14 insertions(+), 1 deletion(-)
diff --git a/migration/migration.c b/migration/migration.c
index e44f77af02..f612313d09 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -126,6 +126,7 @@ static bool migration_object_check(MigrationState *ms, Error **errp);
static int migration_maybe_pause(MigrationState *s,
int *current_active_state,
int new_state);
+static void migrate_fd_cancel(MigrationState *s);
void migration_object_init(void)
{
@@ -169,6 +170,11 @@ void migration_object_init(void)
void migration_object_finalize(void)
{
+ /*
+ * Cancel the current migration - that will (eventually)
+ * stop the migration using this structure
+ */
+ migrate_fd_cancel(current_migration);
object_unref(OBJECT(current_migration));
}
@@ -3134,6 +3140,7 @@ static void *migration_thread(void *opaque)
rcu_register_thread();
+ object_ref(OBJECT(s));
s->iteration_start_time = qemu_clock_get_ms(QEMU_CLOCK_REALTIME);
qemu_savevm_state_header(s->to_dst_file);
@@ -3230,6 +3237,7 @@ static void *migration_thread(void *opaque)
trace_migration_thread_after_loop();
migration_iteration_finish(s);
+ object_unref(OBJECT(s));
rcu_unregister_thread();
return NULL;
}
diff --git a/vl.c b/vl.c
index 2f340686a7..c1920165f3 100644
--- a/vl.c
+++ b/vl.c
@@ -4579,6 +4579,12 @@ int main(int argc, char **argv, char **envp)
gdbserver_cleanup();
+ /*
+ * cleaning up the migration object cancels any existing migration
+ * try to do this early so that it also stops using devices.
+ */
+ migration_object_finalize();
+
/* No more vcpu or device emulation activity beyond this point */
vm_shutdown();
@@ -4594,7 +4600,6 @@ int main(int argc, char **argv, char **envp)
monitor_cleanup();
qemu_chr_cleanup();
user_creatable_cleanup();
- migration_object_finalize();
/* TODO: unref root container, check all devices are ok */
return 0;
--
2.20.1
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: [Qemu-devel] possible ahci/migrate fix
2019-02-27 12:10 [Qemu-devel] possible ahci/migrate fix Dr. David Alan Gilbert
@ 2019-02-27 12:41 ` Juan Quintela
2019-02-27 13:16 ` Dr. David Alan Gilbert
2019-02-27 16:46 ` Alex Bennée
2019-02-27 20:30 ` Juan Quintela
2 siblings, 1 reply; 6+ messages in thread
From: Juan Quintela @ 2019-02-27 12:41 UTC (permalink / raw)
To: Dr. David Alan Gilbert; +Cc: alex.bennee, qemu-devel, peterx
"Dr. David Alan Gilbert" <dgilbert@redhat.com> wrote:
> Hi Alex,
> Can you see if the attached patch fixes the ahci/migrate failure you
> see; it won't fail for me however mean I am to it.
>
>
....
> void migration_object_finalize(void)
> {
> + /*
> + * Cancel the current migration - that will (eventually)
> + * stop the migration using this structure
> + */
> + migrate_fd_cancel(current_migration);
This can only happen during "civilized" exit of qemu, right?
Otherwise, we are changing the migration status.
> object_unref(OBJECT(current_migration));
> }
>
> @@ -3134,6 +3140,7 @@ static void *migration_thread(void *opaque)
>
> rcu_register_thread();
>
> + object_ref(OBJECT(s));
It is weird that this is not enough :-(
> s->iteration_start_time = qemu_clock_get_ms(QEMU_CLOCK_REALTIME);
>
> qemu_savevm_state_header(s->to_dst_file);
> @@ -3230,6 +3237,7 @@ static void *migration_thread(void *opaque)
>
> trace_migration_thread_after_loop();
> migration_iteration_finish(s);
> + object_unref(OBJECT(s));
> rcu_unregister_thread();
> return NULL;
> }
> diff --git a/vl.c b/vl.c
> index 2f340686a7..c1920165f3 100644
> --- a/vl.c
> +++ b/vl.c
> @@ -4579,6 +4579,12 @@ int main(int argc, char **argv, char **envp)
>
> gdbserver_cleanup();
>
> + /*
> + * cleaning up the migration object cancels any existing migration
> + * try to do this early so that it also stops using devices.
> + */
> + migration_object_finalize();
> +
> /* No more vcpu or device emulation activity beyond this point */
> vm_shutdown();
>
> @@ -4594,7 +4600,6 @@ int main(int argc, char **argv, char **envp)
> monitor_cleanup();
> qemu_chr_cleanup();
> user_creatable_cleanup();
> - migration_object_finalize();
> /* TODO: unref root container, check all devices are ok */
>
> return 0;
Ok, it was happening really late.
Once that you are at this, can we rename it?
migration_cleanup()
looks more consistent with everything else, and makes sure that it does
"more" than finalize the object, no?
Furthermore, it is enough to "just" cancel the migration? It is not
needed that we wait for the migration thread to finish?
If the problem was that migration_thread() was accessing the object
after main thread freed it, then just the ref counting should be enough,
no? My understanding is that returning from main is the quivalent of
exit() and kill all threads? Or are we doing something special for that
not to happen?
Later, Juan.
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [Qemu-devel] possible ahci/migrate fix
2019-02-27 12:41 ` Juan Quintela
@ 2019-02-27 13:16 ` Dr. David Alan Gilbert
0 siblings, 0 replies; 6+ messages in thread
From: Dr. David Alan Gilbert @ 2019-02-27 13:16 UTC (permalink / raw)
To: Juan Quintela; +Cc: alex.bennee, qemu-devel, peterx
* Juan Quintela (quintela@redhat.com) wrote:
> "Dr. David Alan Gilbert" <dgilbert@redhat.com> wrote:
> > Hi Alex,
> > Can you see if the attached patch fixes the ahci/migrate failure you
> > see; it won't fail for me however mean I am to it.
> >
> >
>
> ....
>
> > void migration_object_finalize(void)
> > {
> > + /*
> > + * Cancel the current migration - that will (eventually)
> > + * stop the migration using this structure
> > + */
> > + migrate_fd_cancel(current_migration);
>
> This can only happen during "civilized" exit of qemu, right?
> Otherwise, we are changing the migration status.
I'm hoping that, in an exit where:
a) there was no migration this does nothing
b) the migration finished already this does nothing
c) There's a running migration then this causes a cancel.
So if (a) & (b) do nothing then this should be OK, and
if you're trying to do an exit during (c) then it's going bad anyway.
> > object_unref(OBJECT(current_migration));
> > }
> >
> > @@ -3134,6 +3140,7 @@ static void *migration_thread(void *opaque)
> >
> > rcu_register_thread();
> >
> > + object_ref(OBJECT(s));
>
> It is weird that this is not enough :-(
It maybe enough; I was being cautious to add the cancel as well -
I'm pretty sure this series doesn't cover every case, but since these
bugs are hard to reproduce I wanted to try and cover any and all easy
cases. There was a previous attempt (by Fam) 2 years ago which stalled
because we couldn't figure out how to cover everything.
> > s->iteration_start_time = qemu_clock_get_ms(QEMU_CLOCK_REALTIME);
> >
> > qemu_savevm_state_header(s->to_dst_file);
> > @@ -3230,6 +3237,7 @@ static void *migration_thread(void *opaque)
> >
> > trace_migration_thread_after_loop();
> > migration_iteration_finish(s);
> > + object_unref(OBJECT(s));
> > rcu_unregister_thread();
> > return NULL;
> > }
> > diff --git a/vl.c b/vl.c
> > index 2f340686a7..c1920165f3 100644
> > --- a/vl.c
> > +++ b/vl.c
> > @@ -4579,6 +4579,12 @@ int main(int argc, char **argv, char **envp)
> >
> > gdbserver_cleanup();
> >
> > + /*
> > + * cleaning up the migration object cancels any existing migration
> > + * try to do this early so that it also stops using devices.
> > + */
> > + migration_object_finalize();
> > +
> > /* No more vcpu or device emulation activity beyond this point */
> > vm_shutdown();
> >
> > @@ -4594,7 +4600,6 @@ int main(int argc, char **argv, char **envp)
> > monitor_cleanup();
> > qemu_chr_cleanup();
> > user_creatable_cleanup();
> > - migration_object_finalize();
> > /* TODO: unref root container, check all devices are ok */
> >
> > return 0;
>
> Ok, it was happening really late.
>
> Once that you are at this, can we rename it?
>
> migration_cleanup()
>
> looks more consistent with everything else, and makes sure that it does
> "more" than finalize the object, no?
Sure, I'll go with migration_shutdown
> Furthermore, it is enough to "just" cancel the migration? It is not
> needed that we wait for the migration thread to finish?
I agree, but the problem is I don't want to block in the exit path - so
what are the choices?
> If the problem was that migration_thread() was accessing the object
> after main thread freed it, then just the ref counting should be enough,
> no? My understanding is that returning from main is the quivalent of
> exit() and kill all threads? Or are we doing something special for that
> not to happen?
The case Alex saw was gprof having an atexit handler so main hadn't
really exited yet and hadn't killed it's threads; having said that I
can't trigger this even with gprof.
Dave
> Later, Juan.
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [Qemu-devel] possible ahci/migrate fix
2019-02-27 12:10 [Qemu-devel] possible ahci/migrate fix Dr. David Alan Gilbert
2019-02-27 12:41 ` Juan Quintela
@ 2019-02-27 16:46 ` Alex Bennée
2019-02-27 16:51 ` Dr. David Alan Gilbert
2019-02-27 20:30 ` Juan Quintela
2 siblings, 1 reply; 6+ messages in thread
From: Alex Bennée @ 2019-02-27 16:46 UTC (permalink / raw)
To: Dr. David Alan Gilbert; +Cc: qemu-devel, quintela, peterx
Dr. David Alan Gilbert <dgilbert@redhat.com> writes:
> Hi Alex,
> Can you see if the attached patch fixes the ahci/migrate failure you
> see; it won't fail for me however mean I am to it.
over 2000 iterations without issue, commit before crashed within 30
Tested-by: Alex Bennée <alex.bennee@linaro.org>
How quickly can we get this merged?
>
>
> From f4c327d14d656d1c0f0e694d0efc6165493416f0 Mon Sep 17 00:00:00 2001
> From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
> Date: Wed, 27 Feb 2019 12:04:37 +0000
> Subject: [PATCH] migration: Cleanup during exit
>
> Currently we cleanup the migration object as we exit main after the
> main_loop finishes; however if there's a migration running things
> get messy and we can end up with the migration thread still trying
> to access freed structures.
>
> We now take a ref to the object around the migration thread itself,
> so the act of dropping the ref during exit doesn't cause us to lose
> the state until the thread quits.
>
> Cancelling the migration during migration also tries to get the thread
> to quit.
>
> We do this a bit earlier; so hopefully migration gets out of the way
> before all the devices etc are freed.
>
> Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> ---
> migration/migration.c | 8 ++++++++
> vl.c | 7 ++++++-
> 2 files changed, 14 insertions(+), 1 deletion(-)
>
> diff --git a/migration/migration.c b/migration/migration.c
> index e44f77af02..f612313d09 100644
> --- a/migration/migration.c
> +++ b/migration/migration.c
> @@ -126,6 +126,7 @@ static bool migration_object_check(MigrationState *ms, Error **errp);
> static int migration_maybe_pause(MigrationState *s,
> int *current_active_state,
> int new_state);
> +static void migrate_fd_cancel(MigrationState *s);
>
> void migration_object_init(void)
> {
> @@ -169,6 +170,11 @@ void migration_object_init(void)
>
> void migration_object_finalize(void)
> {
> + /*
> + * Cancel the current migration - that will (eventually)
> + * stop the migration using this structure
> + */
> + migrate_fd_cancel(current_migration);
> object_unref(OBJECT(current_migration));
> }
>
> @@ -3134,6 +3140,7 @@ static void *migration_thread(void *opaque)
>
> rcu_register_thread();
>
> + object_ref(OBJECT(s));
> s->iteration_start_time = qemu_clock_get_ms(QEMU_CLOCK_REALTIME);
>
> qemu_savevm_state_header(s->to_dst_file);
> @@ -3230,6 +3237,7 @@ static void *migration_thread(void *opaque)
>
> trace_migration_thread_after_loop();
> migration_iteration_finish(s);
> + object_unref(OBJECT(s));
> rcu_unregister_thread();
> return NULL;
> }
> diff --git a/vl.c b/vl.c
> index 2f340686a7..c1920165f3 100644
> --- a/vl.c
> +++ b/vl.c
> @@ -4579,6 +4579,12 @@ int main(int argc, char **argv, char **envp)
>
> gdbserver_cleanup();
>
> + /*
> + * cleaning up the migration object cancels any existing migration
> + * try to do this early so that it also stops using devices.
> + */
> + migration_object_finalize();
> +
> /* No more vcpu or device emulation activity beyond this point */
> vm_shutdown();
>
> @@ -4594,7 +4600,6 @@ int main(int argc, char **argv, char **envp)
> monitor_cleanup();
> qemu_chr_cleanup();
> user_creatable_cleanup();
> - migration_object_finalize();
> /* TODO: unref root container, check all devices are ok */
>
> return 0;
> --
> 2.20.1
--
Alex Bennée
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [Qemu-devel] possible ahci/migrate fix
2019-02-27 16:46 ` Alex Bennée
@ 2019-02-27 16:51 ` Dr. David Alan Gilbert
0 siblings, 0 replies; 6+ messages in thread
From: Dr. David Alan Gilbert @ 2019-02-27 16:51 UTC (permalink / raw)
To: Alex Bennée, peter.maydell; +Cc: qemu-devel, quintela, peterx
* Alex Bennée (alex.bennee@linaro.org) wrote:
>
> Dr. David Alan Gilbert <dgilbert@redhat.com> writes:
>
> > Hi Alex,
> > Can you see if the attached patch fixes the ahci/migrate failure you
> > see; it won't fail for me however mean I am to it.
>
> over 2000 iterations without issue, commit before crashed within 30
>
> Tested-by: Alex Bennée <alex.bennee@linaro.org>
Great, just reposted as a proper patch.
> How quickly can we get this merged?
Once it gets a review-by I'm happy if someone wants to merge it directly
given the pain it's causing.
Alternatively we'll do a migration pull next week with it.
Dave
> >
> >
> > From f4c327d14d656d1c0f0e694d0efc6165493416f0 Mon Sep 17 00:00:00 2001
> > From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
> > Date: Wed, 27 Feb 2019 12:04:37 +0000
> > Subject: [PATCH] migration: Cleanup during exit
> >
> > Currently we cleanup the migration object as we exit main after the
> > main_loop finishes; however if there's a migration running things
> > get messy and we can end up with the migration thread still trying
> > to access freed structures.
> >
> > We now take a ref to the object around the migration thread itself,
> > so the act of dropping the ref during exit doesn't cause us to lose
> > the state until the thread quits.
> >
> > Cancelling the migration during migration also tries to get the thread
> > to quit.
> >
> > We do this a bit earlier; so hopefully migration gets out of the way
> > before all the devices etc are freed.
> >
> > Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> > ---
> > migration/migration.c | 8 ++++++++
> > vl.c | 7 ++++++-
> > 2 files changed, 14 insertions(+), 1 deletion(-)
> >
> > diff --git a/migration/migration.c b/migration/migration.c
> > index e44f77af02..f612313d09 100644
> > --- a/migration/migration.c
> > +++ b/migration/migration.c
> > @@ -126,6 +126,7 @@ static bool migration_object_check(MigrationState *ms, Error **errp);
> > static int migration_maybe_pause(MigrationState *s,
> > int *current_active_state,
> > int new_state);
> > +static void migrate_fd_cancel(MigrationState *s);
> >
> > void migration_object_init(void)
> > {
> > @@ -169,6 +170,11 @@ void migration_object_init(void)
> >
> > void migration_object_finalize(void)
> > {
> > + /*
> > + * Cancel the current migration - that will (eventually)
> > + * stop the migration using this structure
> > + */
> > + migrate_fd_cancel(current_migration);
> > object_unref(OBJECT(current_migration));
> > }
> >
> > @@ -3134,6 +3140,7 @@ static void *migration_thread(void *opaque)
> >
> > rcu_register_thread();
> >
> > + object_ref(OBJECT(s));
> > s->iteration_start_time = qemu_clock_get_ms(QEMU_CLOCK_REALTIME);
> >
> > qemu_savevm_state_header(s->to_dst_file);
> > @@ -3230,6 +3237,7 @@ static void *migration_thread(void *opaque)
> >
> > trace_migration_thread_after_loop();
> > migration_iteration_finish(s);
> > + object_unref(OBJECT(s));
> > rcu_unregister_thread();
> > return NULL;
> > }
> > diff --git a/vl.c b/vl.c
> > index 2f340686a7..c1920165f3 100644
> > --- a/vl.c
> > +++ b/vl.c
> > @@ -4579,6 +4579,12 @@ int main(int argc, char **argv, char **envp)
> >
> > gdbserver_cleanup();
> >
> > + /*
> > + * cleaning up the migration object cancels any existing migration
> > + * try to do this early so that it also stops using devices.
> > + */
> > + migration_object_finalize();
> > +
> > /* No more vcpu or device emulation activity beyond this point */
> > vm_shutdown();
> >
> > @@ -4594,7 +4600,6 @@ int main(int argc, char **argv, char **envp)
> > monitor_cleanup();
> > qemu_chr_cleanup();
> > user_creatable_cleanup();
> > - migration_object_finalize();
> > /* TODO: unref root container, check all devices are ok */
> >
> > return 0;
> > --
> > 2.20.1
>
>
> --
> Alex Bennée
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [Qemu-devel] possible ahci/migrate fix
2019-02-27 12:10 [Qemu-devel] possible ahci/migrate fix Dr. David Alan Gilbert
2019-02-27 12:41 ` Juan Quintela
2019-02-27 16:46 ` Alex Bennée
@ 2019-02-27 20:30 ` Juan Quintela
2 siblings, 0 replies; 6+ messages in thread
From: Juan Quintela @ 2019-02-27 20:30 UTC (permalink / raw)
To: Dr. David Alan Gilbert; +Cc: alex.bennee, qemu-devel, peterx
"Dr. David Alan Gilbert" <dgilbert@redhat.com> wrote:
> Hi Alex,
> Can you see if the attached patch fixes the ahci/migrate failure you
> see; it won't fail for me however mean I am to it.
Reviewed-by: Juan Quintela <quintela@redhat.com>
It fixes the issue at point, and even if it is not a full solution (not
sure if it is or not), it is a step in the right direction.
Later, Juan.
>
> From f4c327d14d656d1c0f0e694d0efc6165493416f0 Mon Sep 17 00:00:00 2001
> From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
> Date: Wed, 27 Feb 2019 12:04:37 +0000
> Subject: [PATCH] migration: Cleanup during exit
>
> Currently we cleanup the migration object as we exit main after the
> main_loop finishes; however if there's a migration running things
> get messy and we can end up with the migration thread still trying
> to access freed structures.
>
> We now take a ref to the object around the migration thread itself,
> so the act of dropping the ref during exit doesn't cause us to lose
> the state until the thread quits.
>
> Cancelling the migration during migration also tries to get the thread
> to quit.
>
> We do this a bit earlier; so hopefully migration gets out of the way
> before all the devices etc are freed.
>
> Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> ---
> migration/migration.c | 8 ++++++++
> vl.c | 7 ++++++-
> 2 files changed, 14 insertions(+), 1 deletion(-)
>
> diff --git a/migration/migration.c b/migration/migration.c
> index e44f77af02..f612313d09 100644
> --- a/migration/migration.c
> +++ b/migration/migration.c
> @@ -126,6 +126,7 @@ static bool migration_object_check(MigrationState *ms, Error **errp);
> static int migration_maybe_pause(MigrationState *s,
> int *current_active_state,
> int new_state);
> +static void migrate_fd_cancel(MigrationState *s);
>
> void migration_object_init(void)
> {
> @@ -169,6 +170,11 @@ void migration_object_init(void)
>
> void migration_object_finalize(void)
> {
> + /*
> + * Cancel the current migration - that will (eventually)
> + * stop the migration using this structure
> + */
> + migrate_fd_cancel(current_migration);
> object_unref(OBJECT(current_migration));
> }
>
> @@ -3134,6 +3140,7 @@ static void *migration_thread(void *opaque)
>
> rcu_register_thread();
>
> + object_ref(OBJECT(s));
> s->iteration_start_time = qemu_clock_get_ms(QEMU_CLOCK_REALTIME);
>
> qemu_savevm_state_header(s->to_dst_file);
> @@ -3230,6 +3237,7 @@ static void *migration_thread(void *opaque)
>
> trace_migration_thread_after_loop();
> migration_iteration_finish(s);
> + object_unref(OBJECT(s));
> rcu_unregister_thread();
> return NULL;
> }
> diff --git a/vl.c b/vl.c
> index 2f340686a7..c1920165f3 100644
> --- a/vl.c
> +++ b/vl.c
> @@ -4579,6 +4579,12 @@ int main(int argc, char **argv, char **envp)
>
> gdbserver_cleanup();
>
> + /*
> + * cleaning up the migration object cancels any existing migration
> + * try to do this early so that it also stops using devices.
> + */
> + migration_object_finalize();
> +
> /* No more vcpu or device emulation activity beyond this point */
> vm_shutdown();
>
> @@ -4594,7 +4600,6 @@ int main(int argc, char **argv, char **envp)
> monitor_cleanup();
> qemu_chr_cleanup();
> user_creatable_cleanup();
> - migration_object_finalize();
> /* TODO: unref root container, check all devices are ok */
>
> return 0;
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2019-02-27 20:27 UTC | newest]
Thread overview: 6+ messages (download: mbox.gz follow: Atom feed
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2019-02-27 12:10 [Qemu-devel] possible ahci/migrate fix Dr. David Alan Gilbert
2019-02-27 12:41 ` Juan Quintela
2019-02-27 13:16 ` Dr. David Alan Gilbert
2019-02-27 16:46 ` Alex Bennée
2019-02-27 16:51 ` Dr. David Alan Gilbert
2019-02-27 20:30 ` Juan Quintela
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