diff options
Diffstat (limited to 'debian/patches-rt/0066-sched-Make-cond_resched_lock-variants-RT-aware.patch')
| -rw-r--r-- | debian/patches-rt/0066-sched-Make-cond_resched_lock-variants-RT-aware.patch | 100 |
1 files changed, 100 insertions, 0 deletions
diff --git a/debian/patches-rt/0066-sched-Make-cond_resched_lock-variants-RT-aware.patch b/debian/patches-rt/0066-sched-Make-cond_resched_lock-variants-RT-aware.patch new file mode 100644 index 000000000..5791c0771 --- /dev/null +++ b/debian/patches-rt/0066-sched-Make-cond_resched_lock-variants-RT-aware.patch @@ -0,0 +1,100 @@ +From d2f27a429d92d9e68a4b5e4dc1018c6edd94050a Mon Sep 17 00:00:00 2001 +From: Thomas Gleixner <tglx@linutronix.de> +Date: Thu, 23 Sep 2021 18:54:44 +0200 +Subject: [PATCH 066/158] sched: Make cond_resched_lock() variants RT aware +Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/5.15/older/patches-5.15.10-rt24.tar.xz + +The __might_resched() checks in the cond_resched_lock() variants use +PREEMPT_LOCK_OFFSET for preempt count offset checking which takes the +preemption disable by the spin_lock() which is still held at that point +into account. + +On PREEMPT_RT enabled kernels spin/rw_lock held sections stay preemptible +which means PREEMPT_LOCK_OFFSET is 0, but that still triggers the +__might_resched() check because that takes RCU read side nesting into +account. + +On RT enabled kernels spin/read/write_lock() issue rcu_read_lock() to +resemble the !RT semantics, which means in cond_resched_lock() the might +resched check will see preempt_count() == 0 and rcu_preempt_depth() == 1. + +Introduce PREEMPT_LOCK_SCHED_OFFSET for those might resched checks and map +them depending on CONFIG_PREEMPT_RT. + +Signed-off-by: Thomas Gleixner <tglx@linutronix.de> +Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> +Link: https://lore.kernel.org/r/20210923165358.305969211@linutronix.de +--- + include/linux/preempt.h | 5 +++-- + include/linux/sched.h | 34 +++++++++++++++++++++++++--------- + 2 files changed, 28 insertions(+), 11 deletions(-) + +diff --git a/include/linux/preempt.h b/include/linux/preempt.h +index 4d244e295e85..031898b38d06 100644 +--- a/include/linux/preempt.h ++++ b/include/linux/preempt.h +@@ -122,9 +122,10 @@ + * The preempt_count offset after spin_lock() + */ + #if !defined(CONFIG_PREEMPT_RT) +-#define PREEMPT_LOCK_OFFSET PREEMPT_DISABLE_OFFSET ++#define PREEMPT_LOCK_OFFSET PREEMPT_DISABLE_OFFSET + #else +-#define PREEMPT_LOCK_OFFSET 0 ++/* Locks on RT do not disable preemption */ ++#define PREEMPT_LOCK_OFFSET 0 + #endif + + /* +diff --git a/include/linux/sched.h b/include/linux/sched.h +index 4dde5e26de8f..2b8c8150792c 100644 +--- a/include/linux/sched.h ++++ b/include/linux/sched.h +@@ -2060,19 +2060,35 @@ extern int __cond_resched_rwlock_write(rwlock_t *lock); + #define MIGHT_RESCHED_RCU_SHIFT 8 + #define MIGHT_RESCHED_PREEMPT_MASK ((1U << MIGHT_RESCHED_RCU_SHIFT) - 1) + +-#define cond_resched_lock(lock) ({ \ +- __might_resched(__FILE__, __LINE__, PREEMPT_LOCK_OFFSET); \ +- __cond_resched_lock(lock); \ ++#ifndef CONFIG_PREEMPT_RT ++/* ++ * Non RT kernels have an elevated preempt count due to the held lock, ++ * but are not allowed to be inside a RCU read side critical section ++ */ ++# define PREEMPT_LOCK_RESCHED_OFFSETS PREEMPT_LOCK_OFFSET ++#else ++/* ++ * spin/rw_lock() on RT implies rcu_read_lock(). The might_sleep() check in ++ * cond_resched*lock() has to take that into account because it checks for ++ * preempt_count() and rcu_preempt_depth(). ++ */ ++# define PREEMPT_LOCK_RESCHED_OFFSETS \ ++ (PREEMPT_LOCK_OFFSET + (1U << MIGHT_RESCHED_RCU_SHIFT)) ++#endif ++ ++#define cond_resched_lock(lock) ({ \ ++ __might_resched(__FILE__, __LINE__, PREEMPT_LOCK_RESCHED_OFFSETS); \ ++ __cond_resched_lock(lock); \ + }) + +-#define cond_resched_rwlock_read(lock) ({ \ +- __might_resched(__FILE__, __LINE__, PREEMPT_LOCK_OFFSET); \ +- __cond_resched_rwlock_read(lock); \ ++#define cond_resched_rwlock_read(lock) ({ \ ++ __might_resched(__FILE__, __LINE__, PREEMPT_LOCK_RESCHED_OFFSETS); \ ++ __cond_resched_rwlock_read(lock); \ + }) + +-#define cond_resched_rwlock_write(lock) ({ \ +- __might_resched(__FILE__, __LINE__, PREEMPT_LOCK_OFFSET); \ +- __cond_resched_rwlock_write(lock); \ ++#define cond_resched_rwlock_write(lock) ({ \ ++ __might_resched(__FILE__, __LINE__, PREEMPT_LOCK_RESCHED_OFFSETS); \ ++ __cond_resched_rwlock_write(lock); \ + }) + + static inline void cond_resched_rcu(void) +-- +2.33.1 + |