[PATCH 06/30] entry: handle lazy rescheduling at user-exit

From: Ankur Arora
Date: Tue Feb 13 2024 - 00:57:07 EST


The scheduling policy for TIF_NEED_RESCHED_LAZY is to allow the
running task to voluntarily schedule out, running it to completion.

For archs with GENERIC_ENTRY, do this by adding a check in
exit_to_user_mode_loop().

Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Originally-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/lkml/87jzshhexi.ffs@tglx/
Signed-off-by: Ankur Arora <ankur.a.arora@xxxxxxxxxx>
---
include/linux/entry-common.h | 2 +-
kernel/entry/common.c | 2 +-
2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/linux/entry-common.h b/include/linux/entry-common.h
index b0fb775a600d..f5bb19369973 100644
--- a/include/linux/entry-common.h
+++ b/include/linux/entry-common.h
@@ -65,7 +65,7 @@
#define EXIT_TO_USER_MODE_WORK \
(_TIF_SIGPENDING | _TIF_NOTIFY_RESUME | _TIF_UPROBE | \
_TIF_NEED_RESCHED | _TIF_PATCH_PENDING | _TIF_NOTIFY_SIGNAL | \
- ARCH_EXIT_TO_USER_MODE_WORK)
+ _TIF_NEED_RESCHED_LAZY | ARCH_EXIT_TO_USER_MODE_WORK)

/**
* arch_enter_from_user_mode - Architecture specific sanity check for user mode regs
diff --git a/kernel/entry/common.c b/kernel/entry/common.c
index 88cb3c88aaa5..5c5befb05410 100644
--- a/kernel/entry/common.c
+++ b/kernel/entry/common.c
@@ -92,7 +92,7 @@ __always_inline unsigned long exit_to_user_mode_loop(struct pt_regs *regs,

local_irq_enable_exit_to_user(ti_work);

- if (ti_work & _TIF_NEED_RESCHED)
+ if (ti_work & (_TIF_NEED_RESCHED | _TIF_NEED_RESCHED_LAZY))
schedule();

if (ti_work & _TIF_UPROBE)
--
2.31.1