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sched: Make cond_resched_lock() variants RT aware

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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: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20210923165358.305969211@linutronix.de
This commit is contained in:
Thomas Gleixner
2021-09-23 18:54:44 +02:00
committed by Peter Zijlstra
parent 50e081b96e
commit 3e9cc688e5
2 changed files with 28 additions and 11 deletions
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5
include/linux/preempt.h
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@@ -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
/*