diff options
Diffstat (limited to 'debian/patches-rt/0004-sched-Provide-rt_mutex-specific-scheduler-helpers.patch')
| -rw-r--r-- | debian/patches-rt/0004-sched-Provide-rt_mutex-specific-scheduler-helpers.patch | 128 |
1 files changed, 128 insertions, 0 deletions
diff --git a/debian/patches-rt/0004-sched-Provide-rt_mutex-specific-scheduler-helpers.patch b/debian/patches-rt/0004-sched-Provide-rt_mutex-specific-scheduler-helpers.patch new file mode 100644 index 0000000000..f61a67ea3f --- /dev/null +++ b/debian/patches-rt/0004-sched-Provide-rt_mutex-specific-scheduler-helpers.patch @@ -0,0 +1,128 @@ +From: Peter Zijlstra <peterz@infradead.org> +Date: Fri, 8 Sep 2023 18:22:51 +0200 +Subject: [PATCH 4/7] sched: Provide rt_mutex specific scheduler helpers +Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/6.6/older/patches-6.6.7-rt18.tar.xz + +With PREEMPT_RT there is a rt_mutex recursion problem where +sched_submit_work() can use an rtlock (aka spinlock_t). More +specifically what happens is: + + mutex_lock() /* really rt_mutex */ + ... + __rt_mutex_slowlock_locked() + task_blocks_on_rt_mutex() + // enqueue current task as waiter + // do PI chain walk + rt_mutex_slowlock_block() + schedule() + sched_submit_work() + ... + spin_lock() /* really rtlock */ + ... + __rt_mutex_slowlock_locked() + task_blocks_on_rt_mutex() + // enqueue current task as waiter *AGAIN* + // *CONFUSION* + +Fix this by making rt_mutex do the sched_submit_work() early, before +it enqueues itself as a waiter -- before it even knows *if* it will +wait. + +[[ basically Thomas' patch but with different naming and a few asserts + added ]] + +Originally-by: Thomas Gleixner <tglx@linutronix.de> +Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> +Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> +Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> +Link: https://lkml.kernel.org/r/20230908162254.999499-5-bigeasy@linutronix.de +--- + include/linux/sched.h | 3 +++ + include/linux/sched/rt.h | 4 ++++ + kernel/sched/core.c | 36 ++++++++++++++++++++++++++++++++---- + 3 files changed, 39 insertions(+), 4 deletions(-) + +--- a/include/linux/sched.h ++++ b/include/linux/sched.h +@@ -911,6 +911,9 @@ struct task_struct { + * ->sched_remote_wakeup gets used, so it can be in this word. + */ + unsigned sched_remote_wakeup:1; ++#ifdef CONFIG_RT_MUTEXES ++ unsigned sched_rt_mutex:1; ++#endif + + /* Bit to tell LSMs we're in execve(): */ + unsigned in_execve:1; +--- a/include/linux/sched/rt.h ++++ b/include/linux/sched/rt.h +@@ -30,6 +30,10 @@ static inline bool task_is_realtime(stru + } + + #ifdef CONFIG_RT_MUTEXES ++extern void rt_mutex_pre_schedule(void); ++extern void rt_mutex_schedule(void); ++extern void rt_mutex_post_schedule(void); ++ + /* + * Must hold either p->pi_lock or task_rq(p)->lock. + */ +--- a/kernel/sched/core.c ++++ b/kernel/sched/core.c +@@ -6724,9 +6724,6 @@ static inline void sched_submit_work(str + static DEFINE_WAIT_OVERRIDE_MAP(sched_map, LD_WAIT_CONFIG); + unsigned int task_flags; + +- if (task_is_running(tsk)) +- return; +- + /* + * Establish LD_WAIT_CONFIG context to ensure none of the code called + * will use a blocking primitive -- which would lead to recursion. +@@ -6784,7 +6781,12 @@ asmlinkage __visible void __sched schedu + { + struct task_struct *tsk = current; + +- sched_submit_work(tsk); ++#ifdef CONFIG_RT_MUTEXES ++ lockdep_assert(!tsk->sched_rt_mutex); ++#endif ++ ++ if (!task_is_running(tsk)) ++ sched_submit_work(tsk); + __schedule_loop(SM_NONE); + sched_update_worker(tsk); + } +@@ -7045,6 +7047,32 @@ static void __setscheduler_prio(struct t + + #ifdef CONFIG_RT_MUTEXES + ++/* ++ * Would be more useful with typeof()/auto_type but they don't mix with ++ * bit-fields. Since it's a local thing, use int. Keep the generic sounding ++ * name such that if someone were to implement this function we get to compare ++ * notes. ++ */ ++#define fetch_and_set(x, v) ({ int _x = (x); (x) = (v); _x; }) ++ ++void rt_mutex_pre_schedule(void) ++{ ++ lockdep_assert(!fetch_and_set(current->sched_rt_mutex, 1)); ++ sched_submit_work(current); ++} ++ ++void rt_mutex_schedule(void) ++{ ++ lockdep_assert(current->sched_rt_mutex); ++ __schedule_loop(SM_NONE); ++} ++ ++void rt_mutex_post_schedule(void) ++{ ++ sched_update_worker(current); ++ lockdep_assert(fetch_and_set(current->sched_rt_mutex, 0)); ++} ++ + static inline int __rt_effective_prio(struct task_struct *pi_task, int prio) + { + if (pi_task) |