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The current mutex implementation has an atomic lock word and a non-atomic owner field. This disparity leads to a number of issues with the current mutex code as it means that we can have a locked mutex without an explicit owner (because the owner field has not been set, or already cleared). This leads to a number of weird corner cases, esp. between the optimistic spinning and debug code. Where the optimistic spinning code needs the owner field updated inside the lock region, the debug code is more relaxed because the whole lock is serialized by the wait_lock. Also, the spinning code itself has a few corner cases where we need to deal with a held lock without an owner field. Furthermore, it becomes even more of a problem when trying to fix starvation cases in the current code. We end up stacking special case on special case. To solve this rework the basic mutex implementation to be a single atomic word that contains the owner and uses the low bits for extra state. This matches how PI futexes and rt_mutex already work. By having the owner an integral part of the lock state a lot of the problems dissapear and we get a better option to deal with starvation cases, direct owner handoff. Changing the basic mutex does however invalidate all the arch specific mutex code; this patch leaves that unused in-place, a later patch will remove that. Tested-by: Jason Low <jason.low2@hpe.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Will Deacon <will.deacon@arm.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: linux-kernel@vger.kernel.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
46 lines
1.5 KiB
C
46 lines
1.5 KiB
C
/*
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* Mutexes: blocking mutual exclusion locks
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*
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* started by Ingo Molnar:
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*
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* Copyright (C) 2004, 2005, 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
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*
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* This file contains mutex debugging related internal declarations,
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* prototypes and inline functions, for the CONFIG_DEBUG_MUTEXES case.
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* More details are in kernel/mutex-debug.c.
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*/
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/*
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* This must be called with lock->wait_lock held.
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*/
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extern void debug_mutex_lock_common(struct mutex *lock,
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struct mutex_waiter *waiter);
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extern void debug_mutex_wake_waiter(struct mutex *lock,
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struct mutex_waiter *waiter);
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extern void debug_mutex_free_waiter(struct mutex_waiter *waiter);
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extern void debug_mutex_add_waiter(struct mutex *lock,
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struct mutex_waiter *waiter,
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struct task_struct *task);
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extern void mutex_remove_waiter(struct mutex *lock, struct mutex_waiter *waiter,
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struct task_struct *task);
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extern void debug_mutex_unlock(struct mutex *lock);
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extern void debug_mutex_init(struct mutex *lock, const char *name,
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struct lock_class_key *key);
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#define spin_lock_mutex(lock, flags) \
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do { \
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struct mutex *l = container_of(lock, struct mutex, wait_lock); \
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\
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DEBUG_LOCKS_WARN_ON(in_interrupt()); \
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local_irq_save(flags); \
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arch_spin_lock(&(lock)->rlock.raw_lock);\
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DEBUG_LOCKS_WARN_ON(l->magic != l); \
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} while (0)
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#define spin_unlock_mutex(lock, flags) \
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do { \
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arch_spin_unlock(&(lock)->rlock.raw_lock); \
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local_irq_restore(flags); \
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preempt_check_resched(); \
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} while (0)
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