diff options
Diffstat (limited to 'kernel/locking')
| -rw-r--r-- | kernel/locking/mutex.c | 12 | ||||
| -rw-r--r-- | kernel/locking/osq_lock.c | 35 | ||||
| -rw-r--r-- | kernel/locking/rwsem-xadd.c | 35 | ||||
| -rw-r--r-- | kernel/locking/spinlock_debug.c | 14 |
4 files changed, 94 insertions, 2 deletions
diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c index f42f83a36506..bf5277ee11d3 100644 --- a/kernel/locking/mutex.c +++ b/kernel/locking/mutex.c @@ -26,6 +26,7 @@ #include <linux/interrupt.h> #include <linux/debug_locks.h> #include <linux/osq_lock.h> +#include <linux/delay.h> /* * In the DEBUG case we are using the "NULL fastpath" for mutexes, @@ -378,6 +379,17 @@ static bool mutex_optimistic_spin(struct mutex *lock, * values at the cost of a few extra spins. */ cpu_relax_lowlatency(); + + /* + * On arm systems, we must slow down the waiter's repeated + * aquisition of spin_mlock and atomics on the lock count, or + * we risk starving out a thread attempting to release the + * mutex. The mutex slowpath release must take spin lock + * wait_lock. This spin lock can share a monitor with the + * other waiter atomics in the mutex data structure, so must + * take care to rate limit the waiters. + */ + udelay(1); } osq_unlock(&lock->osq); diff --git a/kernel/locking/osq_lock.c b/kernel/locking/osq_lock.c index 05a37857ab55..1e6a51cc25c4 100644 --- a/kernel/locking/osq_lock.c +++ b/kernel/locking/osq_lock.c @@ -1,6 +1,7 @@ #include <linux/percpu.h> #include <linux/sched.h> #include <linux/osq_lock.h> +#include <linux/sched/rt.h> /* * An MCS like lock especially tailored for optimistic spinning for sleeping @@ -85,6 +86,7 @@ bool osq_lock(struct optimistic_spin_queue *lock) { struct optimistic_spin_node *node = this_cpu_ptr(&osq_node); struct optimistic_spin_node *prev, *next; + struct task_struct *task = current; int curr = encode_cpu(smp_processor_id()); int old; @@ -104,6 +106,32 @@ bool osq_lock(struct optimistic_spin_queue *lock) prev = decode_cpu(old); node->prev = prev; + + /* + * We need to avoid reordering of link updation sequence of osq. + * A case in which the status of optimistic spin queue is + * CPU6->CPU2 in which CPU6 has acquired the lock. At this point + * if CPU0 comes in to acquire osq_lock, it will update the tail + * count. After tail count update if CPU2 starts to unqueue itself + * from optimistic spin queue, it will find updated tail count with + * CPU0 and update CPU2 node->next to NULL in osq_wait_next(). If + * reordering of following stores happen then prev->next where prev + * being CPU2 would be updated to point to CPU0 node: + * node->prev = prev; + * WRITE_ONCE(prev->next, node); + * + * At this point if next instruction + * WRITE_ONCE(next->prev, prev); + * in CPU2 path is committed before the update of CPU0 node->prev = + * prev then CPU0 node->prev will point to CPU6 node. At this point + * if CPU0 path's node->prev = prev is committed resulting in change + * of CPU0 prev back to CPU2 node. CPU2 node->next is NULL, so if + * CPU0 gets into unqueue path of osq_lock it will keep spinning + * in infinite loop as condition prev->next == node will never be + * true. + */ + smp_mb(); + WRITE_ONCE(prev->next, node); /* @@ -118,8 +146,13 @@ bool osq_lock(struct optimistic_spin_queue *lock) while (!READ_ONCE(node->locked)) { /* * If we need to reschedule bail... so we can block. + * If a task spins on owner on a CPU after acquiring + * osq_lock while a RT task spins on another CPU to + * acquire osq_lock, it will starve the owner from + * completing if owner is to be scheduled on the same CPU. + * It will be a live lock. */ - if (need_resched()) + if (need_resched() || rt_task(task)) goto unqueue; cpu_relax_lowlatency(); diff --git a/kernel/locking/rwsem-xadd.c b/kernel/locking/rwsem-xadd.c index a4d4de05b2d1..75c950ede9c7 100644 --- a/kernel/locking/rwsem-xadd.c +++ b/kernel/locking/rwsem-xadd.c @@ -511,6 +511,41 @@ struct rw_semaphore *rwsem_wake(struct rw_semaphore *sem) unsigned long flags; /* + * If a spinner is present, there is a chance that the load of + * rwsem_has_spinner() in rwsem_wake() can be reordered with + * respect to decrement of rwsem count in __up_write() leading + * to wakeup being missed. + * + * spinning writer up_write caller + * --------------- ----------------------- + * [S] osq_unlock() [L] osq + * spin_lock(wait_lock) + * sem->count=0xFFFFFFFF00000001 + * +0xFFFFFFFF00000000 + * count=sem->count + * MB + * sem->count=0xFFFFFFFE00000001 + * -0xFFFFFFFF00000001 + * RMB + * spin_trylock(wait_lock) + * return + * rwsem_try_write_lock(count) + * spin_unlock(wait_lock) + * schedule() + * + * Reordering of atomic_long_sub_return_release() in __up_write() + * and rwsem_has_spinner() in rwsem_wake() can cause missing of + * wakeup in up_write() context. In spinning writer, sem->count + * and local variable count is 0XFFFFFFFE00000001. It would result + * in rwsem_try_write_lock() failing to acquire rwsem and spinning + * writer going to sleep in rwsem_down_write_failed(). + * + * The smp_rmb() here is to make sure that the spinner state is + * consulted after sem->count is updated in up_write context. + */ + smp_rmb(); + + /* * If a spinner is present, it is not necessary to do the wakeup. * Try to do wakeup only if the trylock succeeds to minimize * spinlock contention which may introduce too much delay in the diff --git a/kernel/locking/spinlock_debug.c b/kernel/locking/spinlock_debug.c index 0374a596cffa..d381f559e0ce 100644 --- a/kernel/locking/spinlock_debug.c +++ b/kernel/locking/spinlock_debug.c @@ -12,6 +12,8 @@ #include <linux/debug_locks.h> #include <linux/delay.h> #include <linux/export.h> +#include <linux/bug.h> +#include <soc/qcom/watchdog.h> void __raw_spin_lock_init(raw_spinlock_t *lock, const char *name, struct lock_class_key *key) @@ -64,6 +66,11 @@ static void spin_dump(raw_spinlock_t *lock, const char *msg) owner ? owner->comm : "<none>", owner ? task_pid_nr(owner) : -1, lock->owner_cpu); +#ifdef CONFIG_DEBUG_SPINLOCK_BITE_ON_BUG + msm_trigger_wdog_bite(); +#elif defined(CONFIG_DEBUG_SPINLOCK_PANIC_ON_BUG) + BUG(); +#endif dump_stack(); } @@ -114,7 +121,7 @@ static void __spin_lock_debug(raw_spinlock_t *lock) __delay(1); } /* lockup suspected: */ - spin_dump(lock, "lockup suspected"); + spin_bug(lock, "lockup suspected"); #ifdef CONFIG_SMP trigger_all_cpu_backtrace(); #endif @@ -167,6 +174,11 @@ static void rwlock_bug(rwlock_t *lock, const char *msg) printk(KERN_EMERG "BUG: rwlock %s on CPU#%d, %s/%d, %p\n", msg, raw_smp_processor_id(), current->comm, task_pid_nr(current), lock); +#ifdef CONFIG_DEBUG_SPINLOCK_BITE_ON_BUG + msm_trigger_wdog_bite(); +#elif defined(CONFIG_DEBUG_SPINLOCK_PANIC_ON_BUG) + BUG(); +#endif dump_stack(); } |