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SubjectRe: -rt patch scheduler w/ BKL

* Daniel Walker <> wrote:

> The current -rt patch changes the scheduler so that the BKL is no
> longer properly reacquired. If SPINLOCK_BKL is selected it's possible
> for reacquire_kernel_lock() to return without acquiring the BKL, in
> vanilla linux the return value of that function is evaluated, but in
> -rt that code is removed. The result is that if __schedule gets
> recalled on TIF_NEED_RESCHED the BKL will be released unconditionally
> ..

The patch below should fix this. This trylock-the-BKL code predates the
semaphore-based CONFIG_PREEMPT_BKL code - and it's alot better to use
the semaphore than to do a clever trylock loop.


Index: linux/lib/kernel_lock.c
--- linux.orig/lib/kernel_lock.c
+++ linux/lib/kernel_lock.c
@@ -128,11 +128,7 @@ static __cacheline_aligned_in_smp DEFIN
int __lockfunc __reacquire_kernel_lock(void)
- while (!_raw_spin_trylock(&kernel_flag)) {
- if (test_thread_flag(TIF_NEED_RESCHED))
- return -EAGAIN;
- cpu_relax();
- }
+ _raw_spin_lock(&kernel_flag);
return 0;
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