[PATCH v2 0/9] entry: preempt_schedule_irq() callers scrub

[PATCH v2 0/9] entry: preempt_schedule_irq() callers scrub

[Valentin Schneider]

I've left this to ~rot~ age out in the sun for a while, apologies for that.
One early new-year resolution for me is to maintain a shorter resend
timeout on this.


This is the continuation of [1] where I'm hunting down
preempt_schedule_irq() callers because of [2]. 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 5.3 mainline contains those for:
- arm64
- mips
- x86
- powerpc
- nds32

I've also got acks/reviews but haven't seen in any tree yet for:
- c6x
- csky
- riscv
- xtensa

The remaining ones for which I haven't had any reply at all are
- h8300
- microblaze
- sh
- sh64

Build-tested:
- h8300
- c6x
- microblaze
- riscv

No major change since v1 other than rebasing on top of 5.4 and collecting
Reviewed-By / Acked-By.

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 (9):
  sched/core: Fix preempt_schedule() interrupt return comment
  c6x: entry: Remove unneeded need_resched() loop
  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
  xtensa: entry: Remove unneeded need_resched() loop

 arch/c6x/kernel/entry.S        | 3 +--
 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 +---
 arch/xtensa/kernel/entry.S     | 2 +-
 kernel/sched/core.c            | 7 +++----
 9 files changed, 9 insertions(+), 27 deletions(-)

--
2.22.0


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[PATCH v2 1/9] 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.

Acked-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
---
 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 f9a1346a5fa9..3f40ea9f1372 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4223,9 +4223,8 @@ static void __sched notrace preempt_schedule_common(void)
 
 #ifdef CONFIG_PREEMPTION
 /*
- * 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)
 {
@@ -4296,7 +4295,7 @@ EXPORT_SYMBOL_GPL(preempt_schedule_notrace);
 #endif /* CONFIG_PREEMPTION */
 
 /*
- * 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.
--
2.22.0


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[tip: sched/urgent] sched/core: Fix preempt_schedule() interrupt return comment

[tip-bot2 for Valentin Schneider]

The following commit has been merged into the sched/urgent branch of tip:

Commit-ID:     a49b4f4012ef233143c5f7ce44f97851e54d5ef9
Gitweb:        https://git.kernel.org/tip/a49b4f4012ef233143c5f7ce44f97851e54d5ef9
Author:        Valentin Schneider <valentin.schneider@arm.com>
AuthorDate:    Mon, 23 Sep 2019 15:36:12 +01:00
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Wed, 25 Sep 2019 17:42:32 +02:00

sched/core: Fix preempt_schedule() interrupt return comment

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>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: linux-m68k@lists.linux-m68k.org
Cc: linux-riscv@lists.infradead.org
Cc: uclinux-h8-devel@lists.sourceforge.jp
Link: https://lkml.kernel.org/r/20190923143620.29334-2-valentin.schneider@arm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 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 83ea23e..00ef44c 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4218,9 +4218,8 @@ static void __sched notrace preempt_schedule_common(void)
 
 #ifdef CONFIG_PREEMPTION
 /*
- * 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)
 {
@@ -4291,7 +4290,7 @@ EXPORT_SYMBOL_GPL(preempt_schedule_notrace);
 #endif /* CONFIG_PREEMPTION */
 
 /*
- * 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.

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[PATCH v2 6/9] 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.

Reviewed-by: Palmer Dabbelt <palmer@sifive.com>
Signed-off-by: Valentin Schneider <valentin.schneider@arm.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 74ccfd464071..d0523167d261 100644
--- a/arch/riscv/kernel/entry.S
+++ b/arch/riscv/kernel/entry.S
@@ -250,12 +250,11 @@ 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:
-- 
2.22.0


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Re: [PATCH v2 6/9] RISC-V: entry: Remove unneeded need_resched() loop

[Paul Walmsley]

On Mon, 23 Sep 2019, 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.
> 
> Reviewed-by: Palmer Dabbelt <palmer@sifive.com>
> Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
> Cc: Albert Ou <aou@eecs.berkeley.edu>
> Cc: linux-riscv@lists.infradead.org

Thanks, queued for v5.4-rc.


- Paul

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