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c1e2f0eaf0
Julia reported futex state corruption in the following scenario:
waiter waker stealer (prio > waiter)
futex(WAIT_REQUEUE_PI, uaddr, uaddr2,
timeout=[N ms])
futex_wait_requeue_pi()
futex_wait_queue_me()
freezable_schedule()
<scheduled out>
futex(LOCK_PI, uaddr2)
futex(CMP_REQUEUE_PI, uaddr,
uaddr2, 1, 0)
/* requeues waiter to uaddr2 */
futex(UNLOCK_PI, uaddr2)
wake_futex_pi()
cmp_futex_value_locked(uaddr2, waiter)
wake_up_q()
<woken by waker>
<hrtimer_wakeup() fires,
clears sleeper->task>
futex(LOCK_PI, uaddr2)
__rt_mutex_start_proxy_lock()
try_to_take_rt_mutex() /* steals lock */
rt_mutex_set_owner(lock, stealer)
<preempted>
<scheduled in>
rt_mutex_wait_proxy_lock()
__rt_mutex_slowlock()
try_to_take_rt_mutex() /* fails, lock held by stealer */
if (timeout && !timeout->task)
return -ETIMEDOUT;
fixup_owner()
/* lock wasn't acquired, so,
fixup_pi_state_owner skipped */
return -ETIMEDOUT;
/* At this point, we've returned -ETIMEDOUT to userspace, but the
* futex word shows waiter to be the owner, and the pi_mutex has
* stealer as the owner */
futex_lock(LOCK_PI, uaddr2)
-> bails with EDEADLK, futex word says we're owner.
And suggested that what commit:
73d786bd04 ("futex: Rework inconsistent rt_mutex/futex_q state")
removes from fixup_owner() looks to be just what is needed. And indeed
it is -- I completely missed that requeue_pi could also result in this
case. So we need to restore that, except that subsequent patches, like
commit:
16ffa12d74 ("futex: Pull rt_mutex_futex_unlock() out from under hb->lock")
changed all the locking rules. Even without that, the sequence:
- if (rt_mutex_futex_trylock(&q->pi_state->pi_mutex)) {
- locked = 1;
- goto out;
- }
- raw_spin_lock_irq(&q->pi_state->pi_mutex.wait_lock);
- owner = rt_mutex_owner(&q->pi_state->pi_mutex);
- if (!owner)
- owner = rt_mutex_next_owner(&q->pi_state->pi_mutex);
- raw_spin_unlock_irq(&q->pi_state->pi_mutex.wait_lock);
- ret = fixup_pi_state_owner(uaddr, q, owner);
already suggests there were races; otherwise we'd never have to look
at next_owner.
So instead of doing 3 consecutive wait_lock sections with who knows
what races, we do it all in a single section. Additionally, the usage
of pi_state->owner in fixup_owner() was only safe because only the
rt_mutex owner would modify it, which this additional case wrecks.
Luckily the values can only change away and not to the value we're
testing, this means we can do a speculative test and double check once
we have the wait_lock.
Fixes: 73d786bd04 ("futex: Rework inconsistent rt_mutex/futex_q state")
Reported-by: Julia Cartwright <julia@ni.com>
Reported-by: Gratian Crisan <gratian.crisan@ni.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Julia Cartwright <julia@ni.com>
Tested-by: Gratian Crisan <gratian.crisan@ni.com>
Cc: Darren Hart <dvhart@infradead.org>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/20171208124939.7livp7no2ov65rrc@hirez.programming.kicks-ass.net
166 lines
4.2 KiB
C
166 lines
4.2 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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/*
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* RT Mutexes: blocking mutual exclusion locks with PI support
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*
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* started by Ingo Molnar and Thomas Gleixner:
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*
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* Copyright (C) 2004-2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
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* Copyright (C) 2006, Timesys Corp., Thomas Gleixner <tglx@timesys.com>
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*
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* This file contains the private data structure and API definitions.
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*/
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#ifndef __KERNEL_RTMUTEX_COMMON_H
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#define __KERNEL_RTMUTEX_COMMON_H
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#include <linux/rtmutex.h>
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#include <linux/sched/wake_q.h>
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/*
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* This is the control structure for tasks blocked on a rt_mutex,
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* which is allocated on the kernel stack on of the blocked task.
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*
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* @tree_entry: pi node to enqueue into the mutex waiters tree
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* @pi_tree_entry: pi node to enqueue into the mutex owner waiters tree
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* @task: task reference to the blocked task
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*/
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struct rt_mutex_waiter {
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struct rb_node tree_entry;
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struct rb_node pi_tree_entry;
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struct task_struct *task;
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struct rt_mutex *lock;
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#ifdef CONFIG_DEBUG_RT_MUTEXES
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unsigned long ip;
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struct pid *deadlock_task_pid;
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struct rt_mutex *deadlock_lock;
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#endif
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int prio;
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u64 deadline;
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};
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/*
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* Various helpers to access the waiters-tree:
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*/
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#ifdef CONFIG_RT_MUTEXES
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static inline int rt_mutex_has_waiters(struct rt_mutex *lock)
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{
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return !RB_EMPTY_ROOT(&lock->waiters.rb_root);
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}
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static inline struct rt_mutex_waiter *
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rt_mutex_top_waiter(struct rt_mutex *lock)
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{
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struct rt_mutex_waiter *w;
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w = rb_entry(lock->waiters.rb_leftmost,
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struct rt_mutex_waiter, tree_entry);
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BUG_ON(w->lock != lock);
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return w;
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}
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static inline int task_has_pi_waiters(struct task_struct *p)
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{
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return !RB_EMPTY_ROOT(&p->pi_waiters.rb_root);
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}
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static inline struct rt_mutex_waiter *
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task_top_pi_waiter(struct task_struct *p)
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{
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return rb_entry(p->pi_waiters.rb_leftmost,
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struct rt_mutex_waiter, pi_tree_entry);
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}
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#else
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static inline int rt_mutex_has_waiters(struct rt_mutex *lock)
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{
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return false;
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}
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static inline struct rt_mutex_waiter *
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rt_mutex_top_waiter(struct rt_mutex *lock)
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{
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return NULL;
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}
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static inline int task_has_pi_waiters(struct task_struct *p)
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{
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return false;
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}
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static inline struct rt_mutex_waiter *
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task_top_pi_waiter(struct task_struct *p)
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{
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return NULL;
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}
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#endif
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/*
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* lock->owner state tracking:
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*/
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#define RT_MUTEX_HAS_WAITERS 1UL
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static inline struct task_struct *rt_mutex_owner(struct rt_mutex *lock)
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{
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unsigned long owner = (unsigned long) READ_ONCE(lock->owner);
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return (struct task_struct *) (owner & ~RT_MUTEX_HAS_WAITERS);
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}
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/*
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* Constants for rt mutex functions which have a selectable deadlock
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* detection.
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*
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* RT_MUTEX_MIN_CHAINWALK: Stops the lock chain walk when there are
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* no further PI adjustments to be made.
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*
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* RT_MUTEX_FULL_CHAINWALK: Invoke deadlock detection with a full
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* walk of the lock chain.
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*/
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enum rtmutex_chainwalk {
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RT_MUTEX_MIN_CHAINWALK,
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RT_MUTEX_FULL_CHAINWALK,
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};
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/*
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* PI-futex support (proxy locking functions, etc.):
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*/
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extern struct task_struct *rt_mutex_next_owner(struct rt_mutex *lock);
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extern void rt_mutex_init_proxy_locked(struct rt_mutex *lock,
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struct task_struct *proxy_owner);
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extern void rt_mutex_proxy_unlock(struct rt_mutex *lock,
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struct task_struct *proxy_owner);
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extern void rt_mutex_init_waiter(struct rt_mutex_waiter *waiter);
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extern int __rt_mutex_start_proxy_lock(struct rt_mutex *lock,
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struct rt_mutex_waiter *waiter,
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struct task_struct *task);
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extern int rt_mutex_start_proxy_lock(struct rt_mutex *lock,
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struct rt_mutex_waiter *waiter,
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struct task_struct *task);
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extern int rt_mutex_wait_proxy_lock(struct rt_mutex *lock,
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struct hrtimer_sleeper *to,
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struct rt_mutex_waiter *waiter);
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extern bool rt_mutex_cleanup_proxy_lock(struct rt_mutex *lock,
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struct rt_mutex_waiter *waiter);
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extern int rt_mutex_futex_trylock(struct rt_mutex *l);
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extern int __rt_mutex_futex_trylock(struct rt_mutex *l);
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extern void rt_mutex_futex_unlock(struct rt_mutex *lock);
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extern bool __rt_mutex_futex_unlock(struct rt_mutex *lock,
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struct wake_q_head *wqh);
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extern void rt_mutex_postunlock(struct wake_q_head *wake_q);
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#ifdef CONFIG_DEBUG_RT_MUTEXES
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# include "rtmutex-debug.h"
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#else
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# include "rtmutex.h"
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#endif
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#endif
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