[PATCH] kallsyms: Fix scheduling with interrupts disabled in self-test

[PATCH] kallsyms: Fix scheduling with interrupts disabled in self-test

[Nicholas Piggin]

kallsyms_on_each* may schedule so must not be called with interrupts
disabled. The iteration function could disable interrupts, but this
also changes lookup_symbol() to match the change to the other timing
code.

Reported-by: Erhard F. <erhard_f@mailbox.org>
Link: https://lore.kernel.org/all/bug-216902-206035@https.bugzilla.kernel.org%2F/
Reported-by: kernel test robot <oliver.sang@intel.com>
Link: https://lore.kernel.org/oe-lkp/202212251728.8d0872ff-oliver.sang@intel.com
Fixes: 30f3bb09778d ("kallsyms: Add self-test facility")
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
---
 kernel/kallsyms_selftest.c | 21 ++++++---------------
 1 file changed, 6 insertions(+), 15 deletions(-)

diff --git a/kernel/kallsyms_selftest.c b/kernel/kallsyms_selftest.c
index f35d9cc1aab1..bfbc12da3326 100644
--- a/kernel/kallsyms_selftest.c
+++ b/kernel/kallsyms_selftest.c
@@ -157,14 +157,11 @@ static void test_kallsyms_compression_ratio(void)
 static int lookup_name(void *data, const char *name, struct module *mod, unsigned long addr)
 {
 	u64 t0, t1, t;
-	unsigned long flags;
 	struct test_stat *stat = (struct test_stat *)data;
 
-	local_irq_save(flags);
-	t0 = sched_clock();
+	t0 = ktime_get_ns();
 	(void)kallsyms_lookup_name(name);
-	t1 = sched_clock();
-	local_irq_restore(flags);
+	t1 = ktime_get_ns();
 
 	t = t1 - t0;
 	if (t < stat->min)
@@ -234,18 +231,15 @@ static int find_symbol(void *data, const char *name, struct module *mod, unsigne
 static void test_perf_kallsyms_on_each_symbol(void)
 {
 	u64 t0, t1;
-	unsigned long flags;
 	struct test_stat stat;
 
 	memset(&stat, 0, sizeof(stat));
 	stat.max = INT_MAX;
 	stat.name = stub_name;
 	stat.perf = 1;
-	local_irq_save(flags);
-	t0 = sched_clock();
+	t0 = ktime_get_ns();
 	kallsyms_on_each_symbol(find_symbol, &stat);
-	t1 = sched_clock();
-	local_irq_restore(flags);
+	t1 = ktime_get_ns();
 	pr_info("kallsyms_on_each_symbol() traverse all: %lld ns\n", t1 - t0);
 }
 
@@ -270,17 +264,14 @@ static int match_symbol(void *data, unsigned long addr)
 static void test_perf_kallsyms_on_each_match_symbol(void)
 {
 	u64 t0, t1;
-	unsigned long flags;
 	struct test_stat stat;
 
 	memset(&stat, 0, sizeof(stat));
 	stat.max = INT_MAX;
 	stat.name = stub_name;
-	local_irq_save(flags);
-	t0 = sched_clock();
+	t0 = ktime_get_ns();
 	kallsyms_on_each_match_symbol(match_symbol, stat.name, &stat);
-	t1 = sched_clock();
-	local_irq_restore(flags);
+	t1 = ktime_get_ns();
 	pr_info("kallsyms_on_each_match_symbol() traverse all: %lld ns\n", t1 - t0);
 }
 
-- 
2.37.2

Re: [PATCH] kallsyms: Fix scheduling with interrupts disabled in self-test

[Erhard F.]

On Thu, 12 Jan 2023 20:54:26 +1000
Nicholas Piggin <npiggin@gmail.com> wrote:

> kallsyms_on_each* may schedule so must not be called with interrupts
> disabled. The iteration function could disable interrupts, but this
> also changes lookup_symbol() to match the change to the other timing
> code.

Just tested your patch. It fixes the problem on the G5. Thanks!

Regards,
Erhard

Re: [PATCH] kallsyms: Fix scheduling with interrupts disabled in self-test

[Luis Chamberlain]

On Thu, Jan 12, 2023 at 08:54:26PM +1000, Nicholas Piggin wrote:
> kallsyms_on_each* may schedule so must not be called with interrupts
> disabled. The iteration function could disable interrupts, but this
> also changes lookup_symbol() to match the change to the other timing
> code.
> 
> Reported-by: Erhard F. <erhard_f@mailbox.org>
> Link: https://lore.kernel.org/all/bug-216902-206035@https.bugzilla.kernel.org%2F/
> Reported-by: kernel test robot <oliver.sang@intel.com>
> Link: https://lore.kernel.org/oe-lkp/202212251728.8d0872ff-oliver.sang@intel.com
> Fixes: 30f3bb09778d ("kallsyms: Add self-test facility")
> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
> ---

Thanks Nicholas!

Petr had just suggested removing this aspect of the selftests, the performance
test as its specific to the config, it doesn't run many times to get an
average and odd things on a system can create different metrics. Zhen Lei
had given up on fixing it and has a patch to instead remove this part of
the selftest.

I still find value in keeping it, but Petr, would like your opinion on
this fix, if we were to keep it.

  Luis

>  kernel/kallsyms_selftest.c | 21 ++++++---------------
>  1 file changed, 6 insertions(+), 15 deletions(-)
> 
> diff --git a/kernel/kallsyms_selftest.c b/kernel/kallsyms_selftest.c
> index f35d9cc1aab1..bfbc12da3326 100644
> --- a/kernel/kallsyms_selftest.c
> +++ b/kernel/kallsyms_selftest.c
> @@ -157,14 +157,11 @@ static void test_kallsyms_compression_ratio(void)
>  static int lookup_name(void *data, const char *name, struct module *mod, unsigned long addr)
>  {
>  	u64 t0, t1, t;
> -	unsigned long flags;
>  	struct test_stat *stat = (struct test_stat *)data;
>  
> -	local_irq_save(flags);
> -	t0 = sched_clock();
> +	t0 = ktime_get_ns();
>  	(void)kallsyms_lookup_name(name);
> -	t1 = sched_clock();
> -	local_irq_restore(flags);
> +	t1 = ktime_get_ns();
>  
>  	t = t1 - t0;
>  	if (t < stat->min)
> @@ -234,18 +231,15 @@ static int find_symbol(void *data, const char *name, struct module *mod, unsigne
>  static void test_perf_kallsyms_on_each_symbol(void)
>  {
>  	u64 t0, t1;
> -	unsigned long flags;
>  	struct test_stat stat;
>  
>  	memset(&stat, 0, sizeof(stat));
>  	stat.max = INT_MAX;
>  	stat.name = stub_name;
>  	stat.perf = 1;
> -	local_irq_save(flags);
> -	t0 = sched_clock();
> +	t0 = ktime_get_ns();
>  	kallsyms_on_each_symbol(find_symbol, &stat);
> -	t1 = sched_clock();
> -	local_irq_restore(flags);
> +	t1 = ktime_get_ns();
>  	pr_info("kallsyms_on_each_symbol() traverse all: %lld ns\n", t1 - t0);
>  }
>  
> @@ -270,17 +264,14 @@ static int match_symbol(void *data, unsigned long addr)
>  static void test_perf_kallsyms_on_each_match_symbol(void)
>  {
>  	u64 t0, t1;
> -	unsigned long flags;
>  	struct test_stat stat;
>  
>  	memset(&stat, 0, sizeof(stat));
>  	stat.max = INT_MAX;
>  	stat.name = stub_name;
> -	local_irq_save(flags);
> -	t0 = sched_clock();
> +	t0 = ktime_get_ns();
>  	kallsyms_on_each_match_symbol(match_symbol, stat.name, &stat);
> -	t1 = sched_clock();
> -	local_irq_restore(flags);
> +	t1 = ktime_get_ns();
>  	pr_info("kallsyms_on_each_match_symbol() traverse all: %lld ns\n", t1 - t0);
>  }
>  
> -- 
> 2.37.2
> 

Re: [PATCH] kallsyms: Fix scheduling with interrupts disabled in self-test

[Petr Mladek]

On Thu 2023-01-12 10:24:43, Luis Chamberlain wrote:
> On Thu, Jan 12, 2023 at 08:54:26PM +1000, Nicholas Piggin wrote:
> > kallsyms_on_each* may schedule so must not be called with interrupts
> > disabled. The iteration function could disable interrupts, but this
> > also changes lookup_symbol() to match the change to the other timing
> > code.
> > 
> > Reported-by: Erhard F. <erhard_f@mailbox.org>
> > Link: https://lore.kernel.org/all/bug-216902-206035@https.bugzilla.kernel.org%2F/
> > Reported-by: kernel test robot <oliver.sang@intel.com>
> > Link: https://lore.kernel.org/oe-lkp/202212251728.8d0872ff-oliver.sang@intel.com
> > Fixes: 30f3bb09778d ("kallsyms: Add self-test facility")
> > Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
> > ---
> 
> Thanks Nicholas!
> 
> Petr had just suggested removing this aspect of the selftests, the performance
> test as its specific to the config, it doesn't run many times to get an
> average and odd things on a system can create different metrics. Zhen Lei
> had given up on fixing it and has a patch to instead remove this part of
> the selftest.
> 
> I still find value in keeping it, but Petr, would like your opinion on
> this fix, if we were to keep it.

I am fine with this fix.

It increases a risk of possible inaccuracy of the measured time.
It would count also time spent on unrelated interrupts and eventual
rescheduling.

Anyway, it is safe at least. I was against the previous attempts to
fix this problem because they might have caused problems for
the rest of the system.

Best Regards,
Petr

Re: [PATCH] kallsyms: Fix scheduling with interrupts disabled in self-test

[Luis Chamberlain]

On Fri, Jan 13, 2023 at 09:44:35AM +0100, Petr Mladek wrote:
> On Thu 2023-01-12 10:24:43, Luis Chamberlain wrote:
> > On Thu, Jan 12, 2023 at 08:54:26PM +1000, Nicholas Piggin wrote:
> > > kallsyms_on_each* may schedule so must not be called with interrupts
> > > disabled. The iteration function could disable interrupts, but this
> > > also changes lookup_symbol() to match the change to the other timing
> > > code.
> > > 
> > > Reported-by: Erhard F. <erhard_f@mailbox.org>
> > > Link: https://lore.kernel.org/all/bug-216902-206035@https.bugzilla.kernel.org%2F/
> > > Reported-by: kernel test robot <oliver.sang@intel.com>
> > > Link: https://lore.kernel.org/oe-lkp/202212251728.8d0872ff-oliver.sang@intel.com
> > > Fixes: 30f3bb09778d ("kallsyms: Add self-test facility")
> > > Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
> > > ---
> > 
> > Thanks Nicholas!
> > 
> > Petr had just suggested removing this aspect of the selftests, the performance
> > test as its specific to the config, it doesn't run many times to get an
> > average and odd things on a system can create different metrics. Zhen Lei
> > had given up on fixing it and has a patch to instead remove this part of
> > the selftest.
> > 
> > I still find value in keeping it, but Petr, would like your opinion on
> > this fix, if we were to keep it.
> 
> I am fine with this fix.

Merged the fix. I'll push to Linus for 6.2-rc4

  Luis