sched: Make RCU nest depth distinct in __might_resched()

For !RT kernels RCU nest depth in __might_resched() is always expected to
be 0, but on RT kernels it can be non zero while the preempt count is
expected to be always 0.

Instead of playing magic games in interpreting the 'preempt_offset'
argument, rename it to 'offsets' and use the lower 8 bits for the expected
preempt count, allow to hand in the expected RCU nest depth in the upper
bits and adopt the __might_resched() code and related checks and printks.

The affected call sites are updated in subsequent steps.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20210923165358.243232823@linutronix.de

diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index f95ee786e4ef725829114e67598b28ed308c5034..e8696e4a45aa0b6a0072e424e54ccc4a4a64a60d 100644 (file)
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -111,7 +111,7 @@ static __always_inline void might_resched(void)
 #endif /* CONFIG_PREEMPT_* */
 
 #ifdef CONFIG_DEBUG_ATOMIC_SLEEP
-extern void __might_resched(const char *file, int line, int preempt_offset);
+extern void __might_resched(const char *file, int line, unsigned int offsets);
 extern void __might_sleep(const char *file, int line);
 extern void __cant_sleep(const char *file, int line, int preempt_offset);
 extern void __cant_migrate(const char *file, int line);
@@ -169,7 +169,7 @@ extern void __cant_migrate(const char *file, int line);
 # define non_block_end() WARN_ON(current->non_block_count-- == 0)
 #else
   static inline void __might_resched(const char *file, int line,
-                                    int preempt_offset) { }
+                                    unsigned int offsets) { }
 static inline void __might_sleep(const char *file, int line) { }
 # define might_sleep() do { might_resched(); } while (0)
 # define cant_sleep() do { } while (0)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 7a989f2487f885d2e28d0e8f731b6af45b2a9b69..b448c7460577e8bb9e09a63bb1ab1d375cdae270 100644 (file)
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -2046,6 +2046,9 @@ extern int __cond_resched_lock(spinlock_t *lock);
 extern int __cond_resched_rwlock_read(rwlock_t *lock);
 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);                                      \

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 0a27cb8f72a9e72e04eac2feda85550ada3364fe..8d3fa0768e5b6200de63c5891461126cdc7e9d2d 100644 (file)
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -9468,12 +9468,6 @@ void __init sched_init(void)
 }
 
 #ifdef CONFIG_DEBUG_ATOMIC_SLEEP
-static inline int preempt_count_equals(int preempt_offset)
-{
-       int nested = preempt_count() + rcu_preempt_depth();
-
-       return (nested == preempt_offset);
-}
 
 void __might_sleep(const char *file, int line)
 {
@@ -9505,7 +9499,16 @@ static void print_preempt_disable_ip(int preempt_offset, unsigned long ip)
        print_ip_sym(KERN_ERR, ip);
 }
 
-void __might_resched(const char *file, int line, int preempt_offset)
+static inline bool resched_offsets_ok(unsigned int offsets)
+{
+       unsigned int nested = preempt_count();
+
+       nested += rcu_preempt_depth() << MIGHT_RESCHED_RCU_SHIFT;
+
+       return nested == offsets;
+}
+
+void __might_resched(const char *file, int line, unsigned int offsets)
 {
        /* Ratelimiting timestamp: */
        static unsigned long prev_jiffy;
@@ -9515,7 +9518,7 @@ void __might_resched(const char *file, int line, int preempt_offset)
        /* WARN_ON_ONCE() by default, no rate limit required: */
        rcu_sleep_check();
 
-       if ((preempt_count_equals(preempt_offset) && !irqs_disabled() &&
+       if ((resched_offsets_ok(offsets) && !irqs_disabled() &&
             !is_idle_task(current) && !current->non_block_count) ||
            system_state == SYSTEM_BOOTING || system_state > SYSTEM_RUNNING ||
            oops_in_progress)
@@ -9534,11 +9537,11 @@ void __might_resched(const char *file, int line, int preempt_offset)
               in_atomic(), irqs_disabled(), current->non_block_count,
               current->pid, current->comm);
        pr_err("preempt_count: %x, expected: %x\n", preempt_count(),
-              preempt_offset);
+              offsets & MIGHT_RESCHED_PREEMPT_MASK);
 
        if (IS_ENABLED(CONFIG_PREEMPT_RCU)) {
-               pr_err("RCU nest depth: %d, expected: 0\n",
-                      rcu_preempt_depth());
+               pr_err("RCU nest depth: %d, expected: %u\n",
+                      rcu_preempt_depth(), offsets >> MIGHT_RESCHED_RCU_SHIFT);
        }
 
        if (task_stack_end_corrupted(current))
@@ -9548,7 +9551,8 @@ void __might_resched(const char *file, int line, int preempt_offset)
        if (irqs_disabled())
                print_irqtrace_events(current);
 
-       print_preempt_disable_ip(preempt_offset, preempt_disable_ip);
+       print_preempt_disable_ip(offsets & MIGHT_RESCHED_PREEMPT_MASK,
+                                preempt_disable_ip);
 
        dump_stack();
        add_taint(TAINT_WARN, LOCKDEP_STILL_OK);