[PATCH RESEND 0/7] entry: preempt_schedule_irq() callers scrub

[PATCH RESEND 0/7] entry: preempt_schedule_irq() callers scrub

[Valentin Schneider]

Hi,

This is the (RESEND of the) continuation of [1] where I'm hunting down
preempt_schedule_irq() callers because of [2].

I told myself the best way to get this moving forward wouldn't be to write
doc about it, but to go write some fixes and get some discussions going,
which is what this patch-set is about.

I've looked at users of preempt_schedule_irq(), and made sure they didn't
have one of those useless loops. The list of offenders is:

$ grep -r -I "preempt_schedule_irq" arch/ | cut -d/ -f2 | sort | uniq

  arc
  arm
  arm64
  c6x
  csky
  h8300
  ia64
  m68k
  microblaze
  mips
  nds32
  nios2
  parisc
  powerpc
  riscv
  s390
  sh
  sparc
  x86
  xtensa

Regarding that loop, archs seem to fall in 3 categories:
A) Those that don't have the loop
B) Those that have a small need_resched() loop around the
   preempt_schedule_irq() callsite
C) Those that branch to some more generic code further up the entry code
   and eventually branch back to preempt_schedule_irq()

arc, m68k, nios2 fall in A)
sparc, ia64, s390 fall in C)
all the others fall in B)

I've written patches for B). As of 5.2-rc2 mainline contains those for:
- arm64
- mips
- x86
- powerpc
- nds32

I've also got acks for:
- c6x
- xtensa

The remaining ones for which I haven't had a reply yet (hence the RESEND) are:
- csky
- h8300
- microblaze
- riscv
- sh
- sh64


Build-tested on:
- h8300
- c6x
- microblaze

Thanks,
Valentin

[1]: https://lore.kernel.org/lkml/20190131182339.9835-1-valentin.schneider@arm.com/
[2]: https://lore.kernel.org/lkml/cc989920-a13b-d53b-db83-1584a7f53edc@arm.com/

Valentin Schneider (7):
  sched/core: Fix preempt_schedule() interrupt return comment
  csky: entry: Remove unneeded need_resched() loop
  h8300: entry: Remove unneeded need_resched() loop
  microblaze: entry: Remove unneeded need_resched() loop
  RISC-V: entry: Remove unneeded need_resched() loop
  sh: entry: Remove unneeded need_resched() loop
  sh64: entry: Remove unneeded need_resched() loop

 arch/csky/kernel/entry.S       | 4 ----
 arch/h8300/kernel/entry.S      | 3 +--
 arch/microblaze/kernel/entry.S | 5 -----
 arch/riscv/kernel/entry.S      | 3 +--
 arch/sh/kernel/cpu/sh5/entry.S | 5 +----
 arch/sh/kernel/entry-common.S  | 4 +---
 kernel/sched/core.c            | 7 +++----
 7 files changed, 7 insertions(+), 24 deletions(-)

--
2.20.1

[PATCH RESEND 1/7] sched/core: Fix preempt_schedule() interrupt return comment

[Valentin Schneider]

preempt_schedule_irq() is the one that should be called on return from
interrupt, clean up the comment to avoid any ambiguity.

Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
---
 kernel/sched/core.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 874c427742a9..55ebc2cfb08c 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3600,9 +3600,8 @@ static void __sched notrace preempt_schedule_common(void)
 
 #ifdef CONFIG_PREEMPT
 /*
- * this is the entry point to schedule() from in-kernel preemption
- * off of preempt_enable. Kernel preemptions off return from interrupt
- * occur there and call schedule directly.
+ * This is the entry point to schedule() from in-kernel preemption
+ * off of preempt_enable.
  */
 asmlinkage __visible void __sched notrace preempt_schedule(void)
 {
@@ -3673,7 +3672,7 @@ EXPORT_SYMBOL_GPL(preempt_schedule_notrace);
 #endif /* CONFIG_PREEMPT */
 
 /*
- * this is the entry point to schedule() from kernel preemption
+ * This is the entry point to schedule() from kernel preemption
  * off of irq context.
  * Note, that this is called and return with irqs disabled. This will
  * protect us against recursive calling from irq.
-- 
2.20.1

Re: [PATCH RESEND 1/7] sched/core: Fix preempt_schedule() interrupt return comment

[Valentin Schneider]

Duh, forgot to cc the relevant folks on this one...

On 28/05/2019 11:48, Valentin Schneider wrote:
> preempt_schedule_irq() is the one that should be called on return from
> interrupt, clean up the comment to avoid any ambiguity.
> 
> Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
> ---
>  kernel/sched/core.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
> 
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 874c427742a9..55ebc2cfb08c 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -3600,9 +3600,8 @@ static void __sched notrace preempt_schedule_common(void)
>  
>  #ifdef CONFIG_PREEMPT
>  /*
> - * this is the entry point to schedule() from in-kernel preemption
> - * off of preempt_enable. Kernel preemptions off return from interrupt
> - * occur there and call schedule directly.
> + * This is the entry point to schedule() from in-kernel preemption
> + * off of preempt_enable.
>   */
>  asmlinkage __visible void __sched notrace preempt_schedule(void)
>  {
> @@ -3673,7 +3672,7 @@ EXPORT_SYMBOL_GPL(preempt_schedule_notrace);
>  #endif /* CONFIG_PREEMPT */
>  
>  /*
> - * this is the entry point to schedule() from kernel preemption
> + * This is the entry point to schedule() from kernel preemption
>   * off of irq context.
>   * Note, that this is called and return with irqs disabled. This will
>   * protect us against recursive calling from irq.
> 

Re: [PATCH RESEND 1/7] sched/core: Fix preempt_schedule() interrupt return comment

[Thomas Gleixner]

On Tue, 28 May 2019, Valentin Schneider wrote:
> Duh, forgot to cc the relevant folks on this one...

Nevertheless:

Acked-by: Thomas Gleixner <tglx@linutronix.de>

> On 28/05/2019 11:48, Valentin Schneider wrote:
> > preempt_schedule_irq() is the one that should be called on return from
> > interrupt, clean up the comment to avoid any ambiguity.
> > 
> > Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
> > ---
> >  kernel/sched/core.c | 7 +++----
> >  1 file changed, 3 insertions(+), 4 deletions(-)
> > 
> > diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> > index 874c427742a9..55ebc2cfb08c 100644
> > --- a/kernel/sched/core.c
> > +++ b/kernel/sched/core.c
> > @@ -3600,9 +3600,8 @@ static void __sched notrace preempt_schedule_common(void)
> >  
> >  #ifdef CONFIG_PREEMPT
> >  /*
> > - * this is the entry point to schedule() from in-kernel preemption
> > - * off of preempt_enable. Kernel preemptions off return from interrupt
> > - * occur there and call schedule directly.
> > + * This is the entry point to schedule() from in-kernel preemption
> > + * off of preempt_enable.
> >   */
> >  asmlinkage __visible void __sched notrace preempt_schedule(void)
> >  {
> > @@ -3673,7 +3672,7 @@ EXPORT_SYMBOL_GPL(preempt_schedule_notrace);
> >  #endif /* CONFIG_PREEMPT */
> >  
> >  /*
> > - * this is the entry point to schedule() from kernel preemption
> > + * This is the entry point to schedule() from kernel preemption
> >   * off of irq context.
> >   * Note, that this is called and return with irqs disabled. This will
> >   * protect us against recursive calling from irq.
> > 
> 

[PATCH RESEND 2/7] csky: entry: Remove unneeded need_resched() loop

[Valentin Schneider]

Since the enabling and disabling of IRQs within preempt_schedule_irq()
is contained in a need_resched() loop, we don't need the outer arch
code loop.

Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
Cc: Guo Ren <guoren@kernel.org>
---
 arch/csky/kernel/entry.S | 4 ----
 1 file changed, 4 deletions(-)

diff --git a/arch/csky/kernel/entry.S b/arch/csky/kernel/entry.S
index a7e84ccccbd8..679afbcc2001 100644
--- a/arch/csky/kernel/entry.S
+++ b/arch/csky/kernel/entry.S
@@ -292,11 +292,7 @@ ENTRY(csky_irq)
 	ldw	r8, (r9, TINFO_FLAGS)
 	btsti	r8, TIF_NEED_RESCHED
 	bf	2f
-1:
 	jbsr	preempt_schedule_irq	/* irq en/disable is done inside */
-	ldw	r7, (r9, TINFO_FLAGS)	/* get new tasks TI_FLAGS */
-	btsti	r7, TIF_NEED_RESCHED
-	bt	1b			/* go again */
 #endif
 2:
 	jmpi	ret_from_exception
-- 
2.20.1

Re: [PATCH RESEND 2/7] csky: entry: Remove unneeded need_resched() loop

[Guo Ren]

Thx Valentin,

You are right, Approved.

Best Regards
 Guo Ren

On Tue, May 28, 2019 at 11:48:43AM +0100, Valentin Schneider wrote:
> Since the enabling and disabling of IRQs within preempt_schedule_irq()
> is contained in a need_resched() loop, we don't need the outer arch
> code loop.
> 
> Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
> Cc: Guo Ren <guoren@kernel.org>
> ---
>  arch/csky/kernel/entry.S | 4 ----
>  1 file changed, 4 deletions(-)
> 
> diff --git a/arch/csky/kernel/entry.S b/arch/csky/kernel/entry.S
> index a7e84ccccbd8..679afbcc2001 100644
> --- a/arch/csky/kernel/entry.S
> +++ b/arch/csky/kernel/entry.S
> @@ -292,11 +292,7 @@ ENTRY(csky_irq)
>  	ldw	r8, (r9, TINFO_FLAGS)
>  	btsti	r8, TIF_NEED_RESCHED
>  	bf	2f
> -1:
>  	jbsr	preempt_schedule_irq	/* irq en/disable is done inside */
> -	ldw	r7, (r9, TINFO_FLAGS)	/* get new tasks TI_FLAGS */
> -	btsti	r7, TIF_NEED_RESCHED
> -	bt	1b			/* go again */
>  #endif
>  2:
>  	jmpi	ret_from_exception
> -- 
> 2.20.1
> 

[PATCH RESEND 3/7] h8300: entry: Remove unneeded need_resched() loop

[Valentin Schneider]

Since the enabling and disabling of IRQs within preempt_schedule_irq()
is contained in a need_resched() loop, we don't need the outer arch
code loop.

Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
Cc: uclinux-h8-devel@lists.sourceforge.jp
---
 arch/h8300/kernel/entry.S | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/arch/h8300/kernel/entry.S b/arch/h8300/kernel/entry.S
index 4ade5f8299ba..6bde028e7d4a 100644
--- a/arch/h8300/kernel/entry.S
+++ b/arch/h8300/kernel/entry.S
@@ -323,7 +323,6 @@ restore_all:
 resume_kernel:
 	mov.l	@(TI_PRE_COUNT:16,er4),er0
 	bne	restore_all:8
-need_resched:
 	mov.l	@(TI_FLAGS:16,er4),er0
 	btst	#TIF_NEED_RESCHED,r0l
 	beq	restore_all:8
@@ -332,7 +331,7 @@ need_resched:
 	mov.l	sp,er0
 	jsr	@set_esp0
 	jsr	@preempt_schedule_irq
-	bra	need_resched:8
+	bra	restore_all:8
 #endif
 
 ret_from_fork:
-- 
2.20.1

[PATCH RESEND 4/7] microblaze: entry: Remove unneeded need_resched() loop

[Valentin Schneider]

Since the enabling and disabling of IRQs within preempt_schedule_irq()
is contained in a need_resched() loop, we don't need the outer arch
code loop.

Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
Cc: Michal Simek <monstr@monstr.eu>
---
 arch/microblaze/kernel/entry.S | 5 -----
 1 file changed, 5 deletions(-)

diff --git a/arch/microblaze/kernel/entry.S b/arch/microblaze/kernel/entry.S
index 4e1b567becd6..de7083bd1d24 100644
--- a/arch/microblaze/kernel/entry.S
+++ b/arch/microblaze/kernel/entry.S
@@ -738,14 +738,9 @@ no_intr_resched:
 	andi	r5, r5, _TIF_NEED_RESCHED;
 	beqi	r5, restore /* if zero jump over */
 
-preempt:
 	/* interrupts are off that's why I am calling preempt_chedule_irq */
 	bralid	r15, preempt_schedule_irq
 	nop
-	lwi	r11, CURRENT_TASK, TS_THREAD_INFO;	/* get thread info */
-	lwi	r5, r11, TI_FLAGS;		/* get flags in thread info */
-	andi	r5, r5, _TIF_NEED_RESCHED;
-	bnei	r5, preempt /* if non zero jump to resched */
 restore:
 #endif
 	VM_OFF /* MS: turn off MMU */
-- 
2.20.1

[PATCH RESEND 5/7] RISC-V: entry: Remove unneeded need_resched() loop

[Valentin Schneider]

Since the enabling and disabling of IRQs within preempt_schedule_irq()
is contained in a need_resched() loop, we don't need the outer arch
code loop.

Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
Cc: Palmer Dabbelt <palmer@sifive.com>
Cc: Albert Ou <aou@eecs.berkeley.edu>
Cc: linux-riscv@lists.infradead.org
---
 arch/riscv/kernel/entry.S | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S
index 1c1ecc238cfa..d0b1b9660283 100644
--- a/arch/riscv/kernel/entry.S
+++ b/arch/riscv/kernel/entry.S
@@ -258,12 +258,11 @@ restore_all:
 resume_kernel:
 	REG_L s0, TASK_TI_PREEMPT_COUNT(tp)
 	bnez s0, restore_all
-need_resched:
 	REG_L s0, TASK_TI_FLAGS(tp)
 	andi s0, s0, _TIF_NEED_RESCHED
 	beqz s0, restore_all
 	call preempt_schedule_irq
-	j need_resched
+	j restore_all
 #endif
 
 work_pending:
-- 
2.20.1

Re: [PATCH RESEND 5/7] RISC-V: entry: Remove unneeded need_resched() loop

[Palmer Dabbelt]

On Tue, 28 May 2019 03:48:46 PDT (-0700), valentin.schneider@arm.com wrote:
> Since the enabling and disabling of IRQs within preempt_schedule_irq()
> is contained in a need_resched() loop, we don't need the outer arch
> code loop.
>
> Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
> Cc: Palmer Dabbelt <palmer@sifive.com>
> Cc: Albert Ou <aou@eecs.berkeley.edu>
> Cc: linux-riscv@lists.infradead.org
> ---
>  arch/riscv/kernel/entry.S | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S
> index 1c1ecc238cfa..d0b1b9660283 100644
> --- a/arch/riscv/kernel/entry.S
> +++ b/arch/riscv/kernel/entry.S
> @@ -258,12 +258,11 @@ restore_all:
>  resume_kernel:
>  	REG_L s0, TASK_TI_PREEMPT_COUNT(tp)
>  	bnez s0, restore_all
> -need_resched:
>  	REG_L s0, TASK_TI_FLAGS(tp)
>  	andi s0, s0, _TIF_NEED_RESCHED
>  	beqz s0, restore_all
>  	call preempt_schedule_irq
> -	j need_resched
> +	j restore_all
>  #endif
>
>  work_pending:

Sorry I missed this the first time around.

Reviewed-by: Palmer Dabbelt <palmer@sifive.com>

Do you want this through the RISC-V tree, or are you going to take it?

Re: [PATCH RESEND 5/7] RISC-V: entry: Remove unneeded need_resched() loop

[Valentin Schneider]

On 30/05/2019 05:09, Palmer Dabbelt wrote:
[...]
> 
> Sorry I missed this the first time around.
> 
> Reviewed-by: Palmer Dabbelt <palmer@sifive.com>
> 
> Do you want this through the RISC-V tree, or are you going to take it?

Thanks! It's a standalone change so this would be fine through your tree.

[PATCH RESEND 6/7] sh: entry: Remove unneeded need_resched() loop

[Valentin Schneider]

Since the enabling and disabling of IRQs within preempt_schedule_irq()
is contained in a need_resched() loop, we don't need the outer arch
code loop.

Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
Cc: Rich Felker <dalias@libc.org>
Cc: linux-sh@vger.kernel.org
---
 arch/sh/kernel/entry-common.S | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/arch/sh/kernel/entry-common.S b/arch/sh/kernel/entry-common.S
index d31f66e82ce5..65a105de52a0 100644
--- a/arch/sh/kernel/entry-common.S
+++ b/arch/sh/kernel/entry-common.S
@@ -93,7 +93,7 @@ ENTRY(resume_kernel)
 	mov.l	@(TI_PRE_COUNT,r8), r0	! current_thread_info->preempt_count
 	tst	r0, r0
 	bf	noresched
-need_resched:
+
 	mov.l	@(TI_FLAGS,r8), r0	! current_thread_info->flags
 	tst	#_TIF_NEED_RESCHED, r0	! need_resched set?
 	bt	noresched
@@ -107,8 +107,6 @@ need_resched:
 	mov.l	1f, r0
 	jsr	@r0			! call preempt_schedule_irq
 	 nop
-	bra	need_resched
-	 nop
 
 noresched:
 	bra	__restore_all
-- 
2.20.1

[PATCH RESEND 7/7] sh64: entry: Remove unneeded need_resched() loop

[Valentin Schneider]

Since the enabling and disabling of IRQs within preempt_schedule_irq()
is contained in a need_resched() loop, we don't need the outer arch
code loop.

Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
Cc: Rich Felker <dalias@libc.org>
Cc: linux-sh@vger.kernel.org
---
 arch/sh/kernel/cpu/sh5/entry.S | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/arch/sh/kernel/cpu/sh5/entry.S b/arch/sh/kernel/cpu/sh5/entry.S
index de68ffdfffbf..40e6d9a7a6a2 100644
--- a/arch/sh/kernel/cpu/sh5/entry.S
+++ b/arch/sh/kernel/cpu/sh5/entry.S
@@ -897,7 +897,6 @@ resume_kernel:
 	ld.l	r6, TI_PRE_COUNT, r7
 	beq/u	r7, ZERO, tr0
 
-need_resched:
 	ld.l	r6, TI_FLAGS, r7
 	movi	(1 << TIF_NEED_RESCHED), r8
 	and	r8, r7, r8
@@ -911,9 +910,7 @@ need_resched:
 	ori	r7, 1, r7
 	ptabs	r7, tr1
 	blink	tr1, LINK
-
-	pta	need_resched, tr1
-	blink	tr1, ZERO
+	blink   tr0, ZERO
 #endif
 
 	.global ret_from_syscall
-- 
2.20.1