diff mbox series

[v2,1/2] rcutorture: Update rcutorture_one_extend_check() for lazy preemption

Message ID 20250224044310.14373-1-boqun.feng@gmail.com (mailing list archive)
State Accepted
Commit 961357e8d22c6481dd0271d3a3f067fc996c30ef
Headers show
Series [v2,1/2] rcutorture: Update rcutorture_one_extend_check() for lazy preemption | expand

Commit Message

Boqun Feng Feb. 24, 2025, 4:43 a.m. UTC 
From: "Paul E. McKenney" <paulmck@kernel.org>

The rcutorture_one_extend_check() function's last check assumes that
if cur_ops->readlock_nesting() returns greater than zero, either the
RCUTORTURE_RDR_RCU_1 or the RCUTORTURE_RDR_RCU_2 bit must be set, that
is, there must be at least one rcu_read_lock() in effect.

This works for preemptible RCU and for non-preemptible RCU running in
a non-preemptible kernel.  But it fails for non-preemptible RCU running
in a preemptible kernel because then RCU's cur_ops->readlock_nesting()
function, which is rcu_torture_readlock_nesting(), will return
the PREEMPT_MASK mask bits from preempt_count().  The result will
be greater than zero if preemption is disabled, including by the
RCUTORTURE_RDR_PREEMPT and RCUTORTURE_RDR_SCHED bits.

This commit therefore adjusts this check to take into account the case
fo non-preemptible RCU running in a preemptible kernel.

[boqun: Fix the if condition and add comment]

Reported-by: kernel test robot <oliver.sang@intel.com>
Closes: https://lore.kernel.org/oe-lkp/202502171415.8ec87c87-lkp@intel.com
Co-developed-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Co-developed-by: Joel Fernandes <joelagnelf@nvidia.com>
Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
---
 kernel/rcu/rcutorture.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

Comments

Paul E. McKenney Feb. 24, 2025, 4:58 a.m. UTC | #1 
On Sun, Feb 23, 2025 at 08:43:09PM -0800, Boqun Feng wrote:
> From: "Paul E. McKenney" <paulmck@kernel.org>
> 
> The rcutorture_one_extend_check() function's last check assumes that
> if cur_ops->readlock_nesting() returns greater than zero, either the
> RCUTORTURE_RDR_RCU_1 or the RCUTORTURE_RDR_RCU_2 bit must be set, that
> is, there must be at least one rcu_read_lock() in effect.
> 
> This works for preemptible RCU and for non-preemptible RCU running in
> a non-preemptible kernel.  But it fails for non-preemptible RCU running
> in a preemptible kernel because then RCU's cur_ops->readlock_nesting()
> function, which is rcu_torture_readlock_nesting(), will return
> the PREEMPT_MASK mask bits from preempt_count().  The result will
> be greater than zero if preemption is disabled, including by the
> RCUTORTURE_RDR_PREEMPT and RCUTORTURE_RDR_SCHED bits.
> 
> This commit therefore adjusts this check to take into account the case
> fo non-preemptible RCU running in a preemptible kernel.
> 
> [boqun: Fix the if condition and add comment]
> 
> Reported-by: kernel test robot <oliver.sang@intel.com>
> Closes: https://lore.kernel.org/oe-lkp/202502171415.8ec87c87-lkp@intel.com
> Co-developed-by: Boqun Feng <boqun.feng@gmail.com>
> Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
> Co-developed-by: Joel Fernandes <joelagnelf@nvidia.com>
> Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>
> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
> Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
> ---
>  kernel/rcu/rcutorture.c | 14 ++++++++++++--
>  1 file changed, 12 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
> index d26fb1d33ed9..280bff706017 100644
> --- a/kernel/rcu/rcutorture.c
> +++ b/kernel/rcu/rcutorture.c
> @@ -1873,6 +1873,8 @@ static void rcu_torture_reader_do_mbchk(long myid, struct rcu_torture *rtp,
>  #define ROEC_ARGS "%s %s: Current %#x  To add %#x  To remove %#x  preempt_count() %#x\n", __func__, s, curstate, new, old, preempt_count()
>  static void rcutorture_one_extend_check(char *s, int curstate, int new, int old, bool insoftirq)
>  {
> +	int mask;
> +
>  	if (!IS_ENABLED(CONFIG_RCU_TORTURE_TEST_CHK_RDR_STATE))
>  		return;
>  
> @@ -1902,8 +1904,16 @@ static void rcutorture_one_extend_check(char *s, int curstate, int new, int old,
>  	WARN_ONCE(cur_ops->extendables &&
>  		  !(curstate & (RCUTORTURE_RDR_PREEMPT | RCUTORTURE_RDR_SCHED)) &&
>  		  (preempt_count() & PREEMPT_MASK), ROEC_ARGS);
> -	WARN_ONCE(cur_ops->readlock_nesting &&
> -		  !(curstate & (RCUTORTURE_RDR_RCU_1 | RCUTORTURE_RDR_RCU_2)) &&
> +
> +	/*
> +	 * non-preemptible RCU in a preemptible kernel uses "preempt_count() &
> +	 * PREEMPT_MASK" as ->readlock_nesting().
> +	 */
> +	mask = RCUTORTURE_RDR_RCU_1 | RCUTORTURE_RDR_RCU_2;
> +	if (!IS_ENABLED(CONFIG_PREEMPT_RCU))

Good catch, thank you, and it looks good to me!

Oliver, you are right, I was looking at the wrong console output.
One of those days, I guess...  :-/

							Thanx, Paul

> +		mask |= RCUTORTURE_RDR_PREEMPT | RCUTORTURE_RDR_SCHED;
> +
> +	WARN_ONCE(cur_ops->readlock_nesting && !(curstate & mask) &&
>  		  cur_ops->readlock_nesting() > 0, ROEC_ARGS);
>  }
>  
> -- 
> 2.39.5 (Apple Git-154)
>
Oliver Sang Feb. 25, 2025, 2:43 a.m. UTC | #2 
hi, Paul, hi, Boqun Feng,

On Sun, Feb 23, 2025 at 08:58:16PM -0800, Paul E. McKenney wrote:
> On Sun, Feb 23, 2025 at 08:43:09PM -0800, Boqun Feng wrote:
> > From: "Paul E. McKenney" <paulmck@kernel.org>
> > 
> > The rcutorture_one_extend_check() function's last check assumes that
> > if cur_ops->readlock_nesting() returns greater than zero, either the
> > RCUTORTURE_RDR_RCU_1 or the RCUTORTURE_RDR_RCU_2 bit must be set, that
> > is, there must be at least one rcu_read_lock() in effect.
> > 
> > This works for preemptible RCU and for non-preemptible RCU running in
> > a non-preemptible kernel.  But it fails for non-preemptible RCU running
> > in a preemptible kernel because then RCU's cur_ops->readlock_nesting()
> > function, which is rcu_torture_readlock_nesting(), will return
> > the PREEMPT_MASK mask bits from preempt_count().  The result will
> > be greater than zero if preemption is disabled, including by the
> > RCUTORTURE_RDR_PREEMPT and RCUTORTURE_RDR_SCHED bits.
> > 
> > This commit therefore adjusts this check to take into account the case
> > fo non-preemptible RCU running in a preemptible kernel.
> > 
> > [boqun: Fix the if condition and add comment]
> > 
> > Reported-by: kernel test robot <oliver.sang@intel.com>
> > Closes: https://lore.kernel.org/oe-lkp/202502171415.8ec87c87-lkp@intel.com
> > Co-developed-by: Boqun Feng <boqun.feng@gmail.com>
> > Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
> > Co-developed-by: Joel Fernandes <joelagnelf@nvidia.com>
> > Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>
> > Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
> > Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
> > ---
> >  kernel/rcu/rcutorture.c | 14 ++++++++++++--
> >  1 file changed, 12 insertions(+), 2 deletions(-)
> > 
> > diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
> > index d26fb1d33ed9..280bff706017 100644
> > --- a/kernel/rcu/rcutorture.c
> > +++ b/kernel/rcu/rcutorture.c
> > @@ -1873,6 +1873,8 @@ static void rcu_torture_reader_do_mbchk(long myid, struct rcu_torture *rtp,
> >  #define ROEC_ARGS "%s %s: Current %#x  To add %#x  To remove %#x  preempt_count() %#x\n", __func__, s, curstate, new, old, preempt_count()
> >  static void rcutorture_one_extend_check(char *s, int curstate, int new, int old, bool insoftirq)
> >  {
> > +	int mask;
> > +
> >  	if (!IS_ENABLED(CONFIG_RCU_TORTURE_TEST_CHK_RDR_STATE))
> >  		return;
> >  
> > @@ -1902,8 +1904,16 @@ static void rcutorture_one_extend_check(char *s, int curstate, int new, int old,
> >  	WARN_ONCE(cur_ops->extendables &&
> >  		  !(curstate & (RCUTORTURE_RDR_PREEMPT | RCUTORTURE_RDR_SCHED)) &&
> >  		  (preempt_count() & PREEMPT_MASK), ROEC_ARGS);
> > -	WARN_ONCE(cur_ops->readlock_nesting &&
> > -		  !(curstate & (RCUTORTURE_RDR_RCU_1 | RCUTORTURE_RDR_RCU_2)) &&
> > +
> > +	/*
> > +	 * non-preemptible RCU in a preemptible kernel uses "preempt_count() &
> > +	 * PREEMPT_MASK" as ->readlock_nesting().
> > +	 */
> > +	mask = RCUTORTURE_RDR_RCU_1 | RCUTORTURE_RDR_RCU_2;
> > +	if (!IS_ENABLED(CONFIG_PREEMPT_RCU))
> 
> Good catch, thank you, and it looks good to me!
> 
> Oliver, you are right, I was looking at the wrong console output.
> One of those days, I guess...  :-/


we tested this new patch-set, and confirmed the WARN we reported is fixed by
whole patch-set. thanks

Tested-by: kernel test robot <oliver.sang@intel.com>


just want to confirm one thing, we applied the patch-set as below:

* b9aa59295f037 rcutorture: Update ->extendables check for lazy preemption
* 5ffd825e807bd rcutorture: Update rcutorture_one_extend_check() for lazy preemption
* c9b55f9da0d2c rcu: limit PREEMPT_RCU configurations

we also made the test upon 5ffd825e807bd, which still shows the similar WARN.
is this expected?

> 
> 							Thanx, Paul
> 
> > +		mask |= RCUTORTURE_RDR_PREEMPT | RCUTORTURE_RDR_SCHED;
> > +
> > +	WARN_ONCE(cur_ops->readlock_nesting && !(curstate & mask) &&
> >  		  cur_ops->readlock_nesting() > 0, ROEC_ARGS);
> >  }
> >  
> > -- 
> > 2.39.5 (Apple Git-154)
> >
Boqun Feng Feb. 25, 2025, 3:37 a.m. UTC | #3 
On Tue, Feb 25, 2025 at 10:43:45AM +0800, Oliver Sang wrote:
> hi, Paul, hi, Boqun Feng,
> 
> On Sun, Feb 23, 2025 at 08:58:16PM -0800, Paul E. McKenney wrote:
> > On Sun, Feb 23, 2025 at 08:43:09PM -0800, Boqun Feng wrote:
> > > From: "Paul E. McKenney" <paulmck@kernel.org>
> > > 
> > > The rcutorture_one_extend_check() function's last check assumes that
> > > if cur_ops->readlock_nesting() returns greater than zero, either the
> > > RCUTORTURE_RDR_RCU_1 or the RCUTORTURE_RDR_RCU_2 bit must be set, that
> > > is, there must be at least one rcu_read_lock() in effect.
> > > 
> > > This works for preemptible RCU and for non-preemptible RCU running in
> > > a non-preemptible kernel.  But it fails for non-preemptible RCU running
> > > in a preemptible kernel because then RCU's cur_ops->readlock_nesting()
> > > function, which is rcu_torture_readlock_nesting(), will return
> > > the PREEMPT_MASK mask bits from preempt_count().  The result will
> > > be greater than zero if preemption is disabled, including by the
> > > RCUTORTURE_RDR_PREEMPT and RCUTORTURE_RDR_SCHED bits.
> > > 
> > > This commit therefore adjusts this check to take into account the case
> > > fo non-preemptible RCU running in a preemptible kernel.
> > > 
> > > [boqun: Fix the if condition and add comment]
> > > 
> > > Reported-by: kernel test robot <oliver.sang@intel.com>
> > > Closes: https://lore.kernel.org/oe-lkp/202502171415.8ec87c87-lkp@intel.com
> > > Co-developed-by: Boqun Feng <boqun.feng@gmail.com>
> > > Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
> > > Co-developed-by: Joel Fernandes <joelagnelf@nvidia.com>
> > > Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>
> > > Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
> > > Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
> > > ---
> > >  kernel/rcu/rcutorture.c | 14 ++++++++++++--
> > >  1 file changed, 12 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
> > > index d26fb1d33ed9..280bff706017 100644
> > > --- a/kernel/rcu/rcutorture.c
> > > +++ b/kernel/rcu/rcutorture.c
> > > @@ -1873,6 +1873,8 @@ static void rcu_torture_reader_do_mbchk(long myid, struct rcu_torture *rtp,
> > >  #define ROEC_ARGS "%s %s: Current %#x  To add %#x  To remove %#x  preempt_count() %#x\n", __func__, s, curstate, new, old, preempt_count()
> > >  static void rcutorture_one_extend_check(char *s, int curstate, int new, int old, bool insoftirq)
> > >  {
> > > +	int mask;
> > > +
> > >  	if (!IS_ENABLED(CONFIG_RCU_TORTURE_TEST_CHK_RDR_STATE))
> > >  		return;
> > >  
> > > @@ -1902,8 +1904,16 @@ static void rcutorture_one_extend_check(char *s, int curstate, int new, int old,
> > >  	WARN_ONCE(cur_ops->extendables &&
> > >  		  !(curstate & (RCUTORTURE_RDR_PREEMPT | RCUTORTURE_RDR_SCHED)) &&
> > >  		  (preempt_count() & PREEMPT_MASK), ROEC_ARGS);
> > > -	WARN_ONCE(cur_ops->readlock_nesting &&
> > > -		  !(curstate & (RCUTORTURE_RDR_RCU_1 | RCUTORTURE_RDR_RCU_2)) &&
> > > +
> > > +	/*
> > > +	 * non-preemptible RCU in a preemptible kernel uses "preempt_count() &
> > > +	 * PREEMPT_MASK" as ->readlock_nesting().
> > > +	 */
> > > +	mask = RCUTORTURE_RDR_RCU_1 | RCUTORTURE_RDR_RCU_2;
> > > +	if (!IS_ENABLED(CONFIG_PREEMPT_RCU))
> > 
> > Good catch, thank you, and it looks good to me!
> > 
> > Oliver, you are right, I was looking at the wrong console output.
> > One of those days, I guess...  :-/
> 
> 
> we tested this new patch-set, and confirmed the WARN we reported is fixed by
> whole patch-set. thanks
> 
> Tested-by: kernel test robot <oliver.sang@intel.com>
> 

Thanks!

> 
> just want to confirm one thing, we applied the patch-set as below:
> 
> * b9aa59295f037 rcutorture: Update ->extendables check for lazy preemption
> * 5ffd825e807bd rcutorture: Update rcutorture_one_extend_check() for lazy preemption
> * c9b55f9da0d2c rcu: limit PREEMPT_RCU configurations
> 
> we also made the test upon 5ffd825e807bd, which still shows the similar WARN.
> is this expected?
> 

Yes, that's expected, and that's why commit b9aa59295f037 is needed,
thank you for the double confirmation.

Regards,
Boqun

> > 
> > 							Thanx, Paul
> > 
> > > +		mask |= RCUTORTURE_RDR_PREEMPT | RCUTORTURE_RDR_SCHED;
> > > +
> > > +	WARN_ONCE(cur_ops->readlock_nesting && !(curstate & mask) &&
> > >  		  cur_ops->readlock_nesting() > 0, ROEC_ARGS);
> > >  }
> > >  
> > > -- 
> > > 2.39.5 (Apple Git-154)
> > >
Oliver Sang Feb. 25, 2025, 6:20 a.m. UTC | #4 
hi, Boqun,

On Mon, Feb 24, 2025 at 07:37:25PM -0800, Boqun Feng wrote:

[...]

> > 
> > * b9aa59295f037 rcutorture: Update ->extendables check for lazy preemption
> > * 5ffd825e807bd rcutorture: Update rcutorture_one_extend_check() for lazy preemption
> > * c9b55f9da0d2c rcu: limit PREEMPT_RCU configurations
> > 
> > we also made the test upon 5ffd825e807bd, which still shows the similar WARN.
> > is this expected?
> > 
> 
> Yes, that's expected, and that's why commit b9aa59295f037 is needed,

thanks a lot for information!

> thank you for the double confirmation.

you are welcome. always our great pleasure :)

> 
> Regards,
> Boqun
> 
> > > 
> > > 							Thanx, Paul
> > > 
> > > > +		mask |= RCUTORTURE_RDR_PREEMPT | RCUTORTURE_RDR_SCHED;
> > > > +
> > > > +	WARN_ONCE(cur_ops->readlock_nesting && !(curstate & mask) &&
> > > >  		  cur_ops->readlock_nesting() > 0, ROEC_ARGS);
> > > >  }
> > > >  
> > > > -- 
> > > > 2.39.5 (Apple Git-154)
> > > > 
>
diff mbox series

Patch

diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index d26fb1d33ed9..280bff706017 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -1873,6 +1873,8 @@  static void rcu_torture_reader_do_mbchk(long myid, struct rcu_torture *rtp,
 #define ROEC_ARGS "%s %s: Current %#x  To add %#x  To remove %#x  preempt_count() %#x\n", __func__, s, curstate, new, old, preempt_count()
 static void rcutorture_one_extend_check(char *s, int curstate, int new, int old, bool insoftirq)
 {
+	int mask;
+
 	if (!IS_ENABLED(CONFIG_RCU_TORTURE_TEST_CHK_RDR_STATE))
 		return;
 
@@ -1902,8 +1904,16 @@  static void rcutorture_one_extend_check(char *s, int curstate, int new, int old,
 	WARN_ONCE(cur_ops->extendables &&
 		  !(curstate & (RCUTORTURE_RDR_PREEMPT | RCUTORTURE_RDR_SCHED)) &&
 		  (preempt_count() & PREEMPT_MASK), ROEC_ARGS);
-	WARN_ONCE(cur_ops->readlock_nesting &&
-		  !(curstate & (RCUTORTURE_RDR_RCU_1 | RCUTORTURE_RDR_RCU_2)) &&
+
+	/*
+	 * non-preemptible RCU in a preemptible kernel uses "preempt_count() &
+	 * PREEMPT_MASK" as ->readlock_nesting().
+	 */
+	mask = RCUTORTURE_RDR_RCU_1 | RCUTORTURE_RDR_RCU_2;
+	if (!IS_ENABLED(CONFIG_PREEMPT_RCU))
+		mask |= RCUTORTURE_RDR_PREEMPT | RCUTORTURE_RDR_SCHED;
+
+	WARN_ONCE(cur_ops->readlock_nesting && !(curstate & mask) &&
 		  cur_ops->readlock_nesting() > 0, ROEC_ARGS);
 }