* [PATCH v2] sched/core: silence a warning in sched_init()
@ 2019-06-25 12:44 Qian Cai
2019-06-25 13:52 ` Peter Zijlstra
2019-07-08 14:32 ` Qian Cai
0 siblings, 2 replies; 8+ messages in thread
From: Qian Cai @ 2019-06-25 12:44 UTC (permalink / raw)
To: mingo, peterz; +Cc: valentin.schneider, linux-kernel, Qian Cai
Compiling a kernel with both FAIR_GROUP_SCHED=n and RT_GROUP_SCHED=n
will generate a warning using W=1,
kernel/sched/core.c: In function 'sched_init':
kernel/sched/core.c:5906:32: warning: variable 'ptr' set but not used
[-Wunused-but-set-variable]
unsigned long alloc_size = 0, ptr;
^~~
It apparently the maintainers don't like the previous fix [1] which
contains ugly idefs, so silence it by appending the __maybe_unused
attribute for it instead.
[1] https://lore.kernel.org/lkml/1559681162-5385-1-git-send-email-cai@lca.pw/
Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>
Signed-off-by: Qian Cai <cai@lca.pw>
---
v2: Incorporate the feedback from Valentin.
kernel/sched/core.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 874c427742a9..12b9b69c8a66 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5903,7 +5903,8 @@ int in_sched_functions(unsigned long addr)
void __init sched_init(void)
{
int i, j;
- unsigned long alloc_size = 0, ptr;
+ unsigned long alloc_size = 0;
+ unsigned long __maybe_unused ptr;
wait_bit_init();
--
1.8.3.1
^ permalink raw reply related [flat|nested] 8+ messages in thread* Re: [PATCH v2] sched/core: silence a warning in sched_init() 2019-06-25 12:44 [PATCH v2] sched/core: silence a warning in sched_init() Qian Cai @ 2019-06-25 13:52 ` Peter Zijlstra 2019-06-25 14:04 ` Qian Cai 2019-07-08 14:32 ` Qian Cai 1 sibling, 1 reply; 8+ messages in thread From: Peter Zijlstra @ 2019-06-25 13:52 UTC (permalink / raw) To: Qian Cai; +Cc: mingo, valentin.schneider, linux-kernel On Tue, Jun 25, 2019 at 08:44:22AM -0400, Qian Cai wrote: > Compiling a kernel with both FAIR_GROUP_SCHED=n and RT_GROUP_SCHED=n > will generate a warning using W=1, > > kernel/sched/core.c: In function 'sched_init': > kernel/sched/core.c:5906:32: warning: variable 'ptr' set but not used > [-Wunused-but-set-variable] > unsigned long alloc_size = 0, ptr; > ^~~ > > It apparently the maintainers don't like the previous fix [1] which > contains ugly idefs, so silence it by appending the __maybe_unused > attribute for it instead. > > Reviewed-by: Valentin Schneider <valentin.schneider@arm.com> > Signed-off-by: Qian Cai <cai@lca.pw> > --- > > v2: Incorporate the feedback from Valentin. > > kernel/sched/core.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index 874c427742a9..12b9b69c8a66 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -5903,7 +5903,8 @@ int in_sched_functions(unsigned long addr) > void __init sched_init(void) > { > int i, j; > - unsigned long alloc_size = 0, ptr; > + unsigned long alloc_size = 0; > + unsigned long __maybe_unused ptr; > That still isn't particularly pretty. Why do we care about W=1 build noise? Some of that seems rather silly, like that -Wmissing-prototype nonsense. As to this one, ideally the compiler would not be stupid, and understand the below, but alas. diff --git a/kernel/sched/core.c b/kernel/sched/core.c index fa43ce3962e7..cb652e165570 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -6369,7 +6369,7 @@ DECLARE_PER_CPU(cpumask_var_t, select_idle_mask); void __init sched_init(void) { - unsigned long alloc_size = 0, ptr; + unsigned long alloc_size = 0; int i; wait_bit_init(); @@ -6381,7 +6381,7 @@ void __init sched_init(void) alloc_size += 2 * nr_cpu_ids * sizeof(void **); #endif if (alloc_size) { - ptr = (unsigned long)kzalloc(alloc_size, GFP_NOWAIT); + unsigned long ptr = (unsigned long)kzalloc(alloc_size, GFP_NOWAIT); #ifdef CONFIG_FAIR_GROUP_SCHED root_task_group.se = (struct sched_entity **)ptr; ^ permalink raw reply related [flat|nested] 8+ messages in thread
* Re: [PATCH v2] sched/core: silence a warning in sched_init() 2019-06-25 13:52 ` Peter Zijlstra @ 2019-06-25 14:04 ` Qian Cai 2019-06-25 14:25 ` Peter Zijlstra 0 siblings, 1 reply; 8+ messages in thread From: Qian Cai @ 2019-06-25 14:04 UTC (permalink / raw) To: Peter Zijlstra; +Cc: mingo, valentin.schneider, linux-kernel On Tue, 2019-06-25 at 15:52 +0200, Peter Zijlstra wrote: > On Tue, Jun 25, 2019 at 08:44:22AM -0400, Qian Cai wrote: > > Compiling a kernel with both FAIR_GROUP_SCHED=n and RT_GROUP_SCHED=n > > will generate a warning using W=1, > > > > kernel/sched/core.c: In function 'sched_init': > > kernel/sched/core.c:5906:32: warning: variable 'ptr' set but not used > > [-Wunused-but-set-variable] > > unsigned long alloc_size = 0, ptr; > > ^~~ > > > > It apparently the maintainers don't like the previous fix [1] which > > contains ugly idefs, so silence it by appending the __maybe_unused > > attribute for it instead. > > > > Reviewed-by: Valentin Schneider <valentin.schneider@arm.com> > > Signed-off-by: Qian Cai <cai@lca.pw> > > --- > > > > v2: Incorporate the feedback from Valentin. > > > > kernel/sched/core.c | 3 ++- > > 1 file changed, 2 insertions(+), 1 deletion(-) > > > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > > index 874c427742a9..12b9b69c8a66 100644 > > --- a/kernel/sched/core.c > > +++ b/kernel/sched/core.c > > @@ -5903,7 +5903,8 @@ int in_sched_functions(unsigned long addr) > > void __init sched_init(void) > > { > > int i, j; > > - unsigned long alloc_size = 0, ptr; > > + unsigned long alloc_size = 0; > > + unsigned long __maybe_unused ptr; > > > > That still isn't particularly pretty. > > Why do we care about W=1 build noise? Some of that seems rather silly, > like that -Wmissing-prototype nonsense. Yes, -Wmissing-prototype makes no sense, but "-Wunused-but-set-variable" is pretty valid to catch certain developer errors. For example, https://lists.linuxfoundation.org/pipermail/iommu/2019-May/035680.html > > As to this one, ideally the compiler would not be stupid, and understand > the below, but alas. Pretty sure that won't work, as the compiler will complain something like, ISO C90 forbids mixed declarations and code > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index fa43ce3962e7..cb652e165570 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -6369,7 +6369,7 @@ DECLARE_PER_CPU(cpumask_var_t, select_idle_mask); > > void __init sched_init(void) > { > - unsigned long alloc_size = 0, ptr; > + unsigned long alloc_size = 0; > int i; > > wait_bit_init(); > @@ -6381,7 +6381,7 @@ void __init sched_init(void) > alloc_size += 2 * nr_cpu_ids * sizeof(void **); > #endif > if (alloc_size) { > - ptr = (unsigned long)kzalloc(alloc_size, GFP_NOWAIT); > + unsigned long ptr = (unsigned long)kzalloc(alloc_size, > GFP_NOWAIT); > > #ifdef CONFIG_FAIR_GROUP_SCHED > root_task_group.se = (struct sched_entity **)ptr; ^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [PATCH v2] sched/core: silence a warning in sched_init() 2019-06-25 14:04 ` Qian Cai @ 2019-06-25 14:25 ` Peter Zijlstra 2019-06-25 15:07 ` Qian Cai 0 siblings, 1 reply; 8+ messages in thread From: Peter Zijlstra @ 2019-06-25 14:25 UTC (permalink / raw) To: Qian Cai; +Cc: mingo, valentin.schneider, linux-kernel On Tue, Jun 25, 2019 at 10:04:19AM -0400, Qian Cai wrote: > On Tue, 2019-06-25 at 15:52 +0200, Peter Zijlstra wrote: > Yes, -Wmissing-prototype makes no sense, but "-Wunused-but-set-variable" is > pretty valid to catch certain developer errors. For example, > > https://lists.linuxfoundation.org/pipermail/iommu/2019-May/035680.html > > > > > As to this one, ideally the compiler would not be stupid, and understand > > the below, but alas. > > Pretty sure that won't work, as the compiler will complain something like, > > ISO C90 forbids mixed declarations and code No, it builds just fine, it's a new block and C allows new variables at every block start -- with the scope of that block. And for our config, alloc_size is an unconditional 0, so it should DCE the whole block and with that our variable. But clearly the passes are the other way around :/ > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > > index fa43ce3962e7..cb652e165570 100644 > > --- a/kernel/sched/core.c > > +++ b/kernel/sched/core.c > > @@ -6369,7 +6369,7 @@ DECLARE_PER_CPU(cpumask_var_t, select_idle_mask); > > > > void __init sched_init(void) > > { > > - unsigned long alloc_size = 0, ptr; > > + unsigned long alloc_size = 0; > > int i; > > > > wait_bit_init(); > > @@ -6381,7 +6381,7 @@ void __init sched_init(void) > > alloc_size += 2 * nr_cpu_ids * sizeof(void **); > > #endif > > if (alloc_size) { > > - ptr = (unsigned long)kzalloc(alloc_size, GFP_NOWAIT); > > + unsigned long ptr = (unsigned long)kzalloc(alloc_size, > > GFP_NOWAIT); > > > > #ifdef CONFIG_FAIR_GROUP_SCHED > > root_task_group.se = (struct sched_entity **)ptr; ^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [PATCH v2] sched/core: silence a warning in sched_init() 2019-06-25 14:25 ` Peter Zijlstra @ 2019-06-25 15:07 ` Qian Cai 2019-06-25 15:57 ` Peter Zijlstra 0 siblings, 1 reply; 8+ messages in thread From: Qian Cai @ 2019-06-25 15:07 UTC (permalink / raw) To: Peter Zijlstra; +Cc: mingo, valentin.schneider, linux-kernel On Tue, 2019-06-25 at 16:25 +0200, Peter Zijlstra wrote: > On Tue, Jun 25, 2019 at 10:04:19AM -0400, Qian Cai wrote: > > On Tue, 2019-06-25 at 15:52 +0200, Peter Zijlstra wrote: > > Yes, -Wmissing-prototype makes no sense, but "-Wunused-but-set-variable" is > > pretty valid to catch certain developer errors. For example, > > > > https://lists.linuxfoundation.org/pipermail/iommu/2019-May/035680.html > > > > > > > > As to this one, ideally the compiler would not be stupid, and understand > > > the below, but alas. > > > > Pretty sure that won't work, as the compiler will complain something like, > > > > ISO C90 forbids mixed declarations and code > > No, it builds just fine, it's a new block and C allows new variables at > every block start -- with the scope of that block. I remember I tried that before but recalled the error code wrong. Here it is, kernel/sched/core.c:5940:17: warning: unused variable 'ptr' [-Wunused-variable] unsigned long ptr = (unsigned long)kzalloc(alloc_size, GFP_NOWAIT); > > And for our config, alloc_size is an unconditional 0, so it should DCE > the whole block and with that our variable. But clearly the passes are > the other way around :/ > > > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > > > index fa43ce3962e7..cb652e165570 100644 > > > --- a/kernel/sched/core.c > > > +++ b/kernel/sched/core.c > > > @@ -6369,7 +6369,7 @@ DECLARE_PER_CPU(cpumask_var_t, select_idle_mask); > > > > > > void __init sched_init(void) > > > { > > > - unsigned long alloc_size = 0, ptr; > > > + unsigned long alloc_size = 0; > > > int i; > > > > > > wait_bit_init(); > > > @@ -6381,7 +6381,7 @@ void __init sched_init(void) > > > alloc_size += 2 * nr_cpu_ids * sizeof(void **); > > > #endif > > > if (alloc_size) { > > > - ptr = (unsigned long)kzalloc(alloc_size, GFP_NOWAIT); > > > + unsigned long ptr = (unsigned long)kzalloc(alloc_size, > > > GFP_NOWAIT); > > > > > > #ifdef CONFIG_FAIR_GROUP_SCHED > > > root_task_group.se = (struct sched_entity **)ptr; ^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [PATCH v2] sched/core: silence a warning in sched_init() 2019-06-25 15:07 ` Qian Cai @ 2019-06-25 15:57 ` Peter Zijlstra 2019-07-18 20:44 ` Qian Cai 0 siblings, 1 reply; 8+ messages in thread From: Peter Zijlstra @ 2019-06-25 15:57 UTC (permalink / raw) To: Qian Cai; +Cc: mingo, valentin.schneider, linux-kernel On Tue, Jun 25, 2019 at 11:07:09AM -0400, Qian Cai wrote: > On Tue, 2019-06-25 at 16:25 +0200, Peter Zijlstra wrote: > > On Tue, Jun 25, 2019 at 10:04:19AM -0400, Qian Cai wrote: > > > On Tue, 2019-06-25 at 15:52 +0200, Peter Zijlstra wrote: > > > Yes, -Wmissing-prototype makes no sense, but "-Wunused-but-set-variable" is > > > pretty valid to catch certain developer errors. For example, > > > > > > https://lists.linuxfoundation.org/pipermail/iommu/2019-May/035680.html > > > > > > > > > > > As to this one, ideally the compiler would not be stupid, and understand > > > > the below, but alas. > > > > > > Pretty sure that won't work, as the compiler will complain something like, > > > > > > ISO C90 forbids mixed declarations and code > > > > No, it builds just fine, it's a new block and C allows new variables at > > every block start -- with the scope of that block. > > I remember I tried that before but recalled the error code wrong. Here it is, > > kernel/sched/core.c:5940:17: warning: unused variable 'ptr' [-Wunused-variable] > unsigned long ptr = (unsigned long)kzalloc(alloc_size, > GFP_NOWAIT); Yes, I know, I tried. And GCC is a moron because of it. ^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [PATCH v2] sched/core: silence a warning in sched_init() 2019-06-25 15:57 ` Peter Zijlstra @ 2019-07-18 20:44 ` Qian Cai 0 siblings, 0 replies; 8+ messages in thread From: Qian Cai @ 2019-07-18 20:44 UTC (permalink / raw) To: Peter Zijlstra; +Cc: mingo, Valentin Schneider, LKML > On Jun 25, 2019, at 11:57 AM, Peter Zijlstra <peterz@infradead.org> wrote: > > On Tue, Jun 25, 2019 at 11:07:09AM -0400, Qian Cai wrote: >> On Tue, 2019-06-25 at 16:25 +0200, Peter Zijlstra wrote: >>> On Tue, Jun 25, 2019 at 10:04:19AM -0400, Qian Cai wrote: >>>> On Tue, 2019-06-25 at 15:52 +0200, Peter Zijlstra wrote: >>>> Yes, -Wmissing-prototype makes no sense, but "-Wunused-but-set-variable" is >>>> pretty valid to catch certain developer errors. For example, >>>> >>>> https://lists.linuxfoundation.org/pipermail/iommu/2019-May/035680.html >>>> >>>>> >>>>> As to this one, ideally the compiler would not be stupid, and understand >>>>> the below, but alas. >>>> >>>> Pretty sure that won't work, as the compiler will complain something like, >>>> >>>> ISO C90 forbids mixed declarations and code >>> >>> No, it builds just fine, it's a new block and C allows new variables at >>> every block start -- with the scope of that block. >> >> I remember I tried that before but recalled the error code wrong. Here it is, >> >> kernel/sched/core.c:5940:17: warning: unused variable 'ptr' [-Wunused-variable] >> unsigned long ptr = (unsigned long)kzalloc(alloc_size, >> GFP_NOWAIT); > > Yes, I know, I tried. And GCC is a moron because of it. Actually, not only GCC but clang also don’t understand your patch. # make CC=clang W=1 kernel/sched/core.o kernel/sched/core.c:6384:17: warning: unused variable 'ptr' [-Wunused-variable] unsigned long ptr = (unsigned long)kzalloc(alloc_size, GFP_NOWAIT); Maybe adding a “__maybe_unused” until the day that compilers are getting smarter. ^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [PATCH v2] sched/core: silence a warning in sched_init() 2019-06-25 12:44 [PATCH v2] sched/core: silence a warning in sched_init() Qian Cai 2019-06-25 13:52 ` Peter Zijlstra @ 2019-07-08 14:32 ` Qian Cai 1 sibling, 0 replies; 8+ messages in thread From: Qian Cai @ 2019-07-08 14:32 UTC (permalink / raw) To: mingo, peterz; +Cc: valentin.schneider, linux-kernel Ping. Per discussion, sounds like this is the best thing to do in order to avoid compilation warnings. On Tue, 2019-06-25 at 08:44 -0400, Qian Cai wrote: > Compiling a kernel with both FAIR_GROUP_SCHED=n and RT_GROUP_SCHED=n > will generate a warning using W=1, > > kernel/sched/core.c: In function 'sched_init': > kernel/sched/core.c:5906:32: warning: variable 'ptr' set but not used > [-Wunused-but-set-variable] > unsigned long alloc_size = 0, ptr; > ^~~ > > It apparently the maintainers don't like the previous fix [1] which > contains ugly idefs, so silence it by appending the __maybe_unused > attribute for it instead. > > [1] https://lore.kernel.org/lkml/1559681162-5385-1-git-send-email-cai@lca.pw/ > > Reviewed-by: Valentin Schneider <valentin.schneider@arm.com> > Signed-off-by: Qian Cai <cai@lca.pw> > --- > > v2: Incorporate the feedback from Valentin. > > kernel/sched/core.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index 874c427742a9..12b9b69c8a66 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -5903,7 +5903,8 @@ int in_sched_functions(unsigned long addr) > void __init sched_init(void) > { > int i, j; > - unsigned long alloc_size = 0, ptr; > + unsigned long alloc_size = 0; > + unsigned long __maybe_unused ptr; > > wait_bit_init(); > ^ permalink raw reply [flat|nested] 8+ messages in thread
end of thread, other threads:[~2019-07-18 20:44 UTC | newest] Thread overview: 8+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2019-06-25 12:44 [PATCH v2] sched/core: silence a warning in sched_init() Qian Cai 2019-06-25 13:52 ` Peter Zijlstra 2019-06-25 14:04 ` Qian Cai 2019-06-25 14:25 ` Peter Zijlstra 2019-06-25 15:07 ` Qian Cai 2019-06-25 15:57 ` Peter Zijlstra 2019-07-18 20:44 ` Qian Cai 2019-07-08 14:32 ` Qian Cai
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