summaryrefslogtreecommitdiff
path: root/kernel/futex/core.c
diff options
context:
space:
mode:
Diffstat (limited to 'kernel/futex/core.c')
-rw-r--r--kernel/futex/core.c536
1 files changed, 1 insertions, 535 deletions
diff --git a/kernel/futex/core.c b/kernel/futex/core.c
index 42f2735e9abf..25d8a88b32e5 100644
--- a/kernel/futex/core.c
+++ b/kernel/futex/core.c
@@ -34,7 +34,6 @@
#include <linux/compat.h>
#include <linux/jhash.h>
#include <linux/pagemap.h>
-#include <linux/freezer.h>
#include <linux/memblock.h>
#include <linux/fault-inject.h>
#include <linux/slab.h>
@@ -42,106 +41,6 @@
#include "futex.h"
#include "../locking/rtmutex_common.h"
-/*
- * READ this before attempting to hack on futexes!
- *
- * Basic futex operation and ordering guarantees
- * =============================================
- *
- * The waiter reads the futex value in user space and calls
- * futex_wait(). This function computes the hash bucket and acquires
- * the hash bucket lock. After that it reads the futex user space value
- * again and verifies that the data has not changed. If it has not changed
- * it enqueues itself into the hash bucket, releases the hash bucket lock
- * and schedules.
- *
- * The waker side modifies the user space value of the futex and calls
- * futex_wake(). This function computes the hash bucket and acquires the
- * hash bucket lock. Then it looks for waiters on that futex in the hash
- * bucket and wakes them.
- *
- * In futex wake up scenarios where no tasks are blocked on a futex, taking
- * the hb spinlock can be avoided and simply return. In order for this
- * optimization to work, ordering guarantees must exist so that the waiter
- * being added to the list is acknowledged when the list is concurrently being
- * checked by the waker, avoiding scenarios like the following:
- *
- * CPU 0 CPU 1
- * val = *futex;
- * sys_futex(WAIT, futex, val);
- * futex_wait(futex, val);
- * uval = *futex;
- * *futex = newval;
- * sys_futex(WAKE, futex);
- * futex_wake(futex);
- * if (queue_empty())
- * return;
- * if (uval == val)
- * lock(hash_bucket(futex));
- * queue();
- * unlock(hash_bucket(futex));
- * schedule();
- *
- * This would cause the waiter on CPU 0 to wait forever because it
- * missed the transition of the user space value from val to newval
- * and the waker did not find the waiter in the hash bucket queue.
- *
- * The correct serialization ensures that a waiter either observes
- * the changed user space value before blocking or is woken by a
- * concurrent waker:
- *
- * CPU 0 CPU 1
- * val = *futex;
- * sys_futex(WAIT, futex, val);
- * futex_wait(futex, val);
- *
- * waiters++; (a)
- * smp_mb(); (A) <-- paired with -.
- * |
- * lock(hash_bucket(futex)); |
- * |
- * uval = *futex; |
- * | *futex = newval;
- * | sys_futex(WAKE, futex);
- * | futex_wake(futex);
- * |
- * `--------> smp_mb(); (B)
- * if (uval == val)
- * queue();
- * unlock(hash_bucket(futex));
- * schedule(); if (waiters)
- * lock(hash_bucket(futex));
- * else wake_waiters(futex);
- * waiters--; (b) unlock(hash_bucket(futex));
- *
- * Where (A) orders the waiters increment and the futex value read through
- * atomic operations (see futex_hb_waiters_inc) and where (B) orders the write
- * to futex and the waiters read (see futex_hb_waiters_pending()).
- *
- * This yields the following case (where X:=waiters, Y:=futex):
- *
- * X = Y = 0
- *
- * w[X]=1 w[Y]=1
- * MB MB
- * r[Y]=y r[X]=x
- *
- * Which guarantees that x==0 && y==0 is impossible; which translates back into
- * the guarantee that we cannot both miss the futex variable change and the
- * enqueue.
- *
- * Note that a new waiter is accounted for in (a) even when it is possible that
- * the wait call can return error, in which case we backtrack from it in (b).
- * Refer to the comment in futex_q_lock().
- *
- * Similarly, in order to account for waiters being requeued on another
- * address we always increment the waiters for the destination bucket before
- * acquiring the lock. It then decrements them again after releasing it -
- * the code that actually moves the futex(es) between hash buckets (requeue_futex)
- * will do the additional required waiter count housekeeping. This is done for
- * double_lock_hb() and double_unlock_hb(), respectively.
- */
-
#ifndef CONFIG_HAVE_FUTEX_CMPXCHG
int __read_mostly futex_cmpxchg_enabled;
#endif
@@ -211,19 +110,6 @@ late_initcall(fail_futex_debugfs);
#endif /* CONFIG_FAIL_FUTEX */
-static inline int futex_hb_waiters_pending(struct futex_hash_bucket *hb)
-{
-#ifdef CONFIG_SMP
- /*
- * Full barrier (B), see the ordering comment above.
- */
- smp_mb();
- return atomic_read(&hb->waiters);
-#else
- return 1;
-#endif
-}
-
/**
* futex_hash - Return the hash bucket in the global hash
* @key: Pointer to the futex key for which the hash is calculated
@@ -628,217 +514,6 @@ void __futex_unqueue(struct futex_q *q)
futex_hb_waiters_dec(hb);
}
-/*
- * The hash bucket lock must be held when this is called.
- * Afterwards, the futex_q must not be accessed. Callers
- * must ensure to later call wake_up_q() for the actual
- * wakeups to occur.
- */
-void futex_wake_mark(struct wake_q_head *wake_q, struct futex_q *q)
-{
- struct task_struct *p = q->task;
-
- if (WARN(q->pi_state || q->rt_waiter, "refusing to wake PI futex\n"))
- return;
-
- get_task_struct(p);
- __futex_unqueue(q);
- /*
- * The waiting task can free the futex_q as soon as q->lock_ptr = NULL
- * is written, without taking any locks. This is possible in the event
- * of a spurious wakeup, for example. A memory barrier is required here
- * to prevent the following store to lock_ptr from getting ahead of the
- * plist_del in __futex_unqueue().
- */
- smp_store_release(&q->lock_ptr, NULL);
-
- /*
- * Queue the task for later wakeup for after we've released
- * the hb->lock.
- */
- wake_q_add_safe(wake_q, p);
-}
-
-/*
- * Wake up waiters matching bitset queued on this futex (uaddr).
- */
-int futex_wake(u32 __user *uaddr, unsigned int flags, int nr_wake, u32 bitset)
-{
- struct futex_hash_bucket *hb;
- struct futex_q *this, *next;
- union futex_key key = FUTEX_KEY_INIT;
- int ret;
- DEFINE_WAKE_Q(wake_q);
-
- if (!bitset)
- return -EINVAL;
-
- ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, FUTEX_READ);
- if (unlikely(ret != 0))
- return ret;
-
- hb = futex_hash(&key);
-
- /* Make sure we really have tasks to wakeup */
- if (!futex_hb_waiters_pending(hb))
- return ret;
-
- spin_lock(&hb->lock);
-
- plist_for_each_entry_safe(this, next, &hb->chain, list) {
- if (futex_match (&this->key, &key)) {
- if (this->pi_state || this->rt_waiter) {
- ret = -EINVAL;
- break;
- }
-
- /* Check if one of the bits is set in both bitsets */
- if (!(this->bitset & bitset))
- continue;
-
- futex_wake_mark(&wake_q, this);
- if (++ret >= nr_wake)
- break;
- }
- }
-
- spin_unlock(&hb->lock);
- wake_up_q(&wake_q);
- return ret;
-}
-
-static int futex_atomic_op_inuser(unsigned int encoded_op, u32 __user *uaddr)
-{
- unsigned int op = (encoded_op & 0x70000000) >> 28;
- unsigned int cmp = (encoded_op & 0x0f000000) >> 24;
- int oparg = sign_extend32((encoded_op & 0x00fff000) >> 12, 11);
- int cmparg = sign_extend32(encoded_op & 0x00000fff, 11);
- int oldval, ret;
-
- if (encoded_op & (FUTEX_OP_OPARG_SHIFT << 28)) {
- if (oparg < 0 || oparg > 31) {
- char comm[sizeof(current->comm)];
- /*
- * kill this print and return -EINVAL when userspace
- * is sane again
- */
- pr_info_ratelimited("futex_wake_op: %s tries to shift op by %d; fix this program\n",
- get_task_comm(comm, current), oparg);
- oparg &= 31;
- }
- oparg = 1 << oparg;
- }
-
- pagefault_disable();
- ret = arch_futex_atomic_op_inuser(op, oparg, &oldval, uaddr);
- pagefault_enable();
- if (ret)
- return ret;
-
- switch (cmp) {
- case FUTEX_OP_CMP_EQ:
- return oldval == cmparg;
- case FUTEX_OP_CMP_NE:
- return oldval != cmparg;
- case FUTEX_OP_CMP_LT:
- return oldval < cmparg;
- case FUTEX_OP_CMP_GE:
- return oldval >= cmparg;
- case FUTEX_OP_CMP_LE:
- return oldval <= cmparg;
- case FUTEX_OP_CMP_GT:
- return oldval > cmparg;
- default:
- return -ENOSYS;
- }
-}
-
-/*
- * Wake up all waiters hashed on the physical page that is mapped
- * to this virtual address:
- */
-int futex_wake_op(u32 __user *uaddr1, unsigned int flags, u32 __user *uaddr2,
- int nr_wake, int nr_wake2, int op)
-{
- union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
- struct futex_hash_bucket *hb1, *hb2;
- struct futex_q *this, *next;
- int ret, op_ret;
- DEFINE_WAKE_Q(wake_q);
-
-retry:
- ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, FUTEX_READ);
- if (unlikely(ret != 0))
- return ret;
- ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, FUTEX_WRITE);
- if (unlikely(ret != 0))
- return ret;
-
- hb1 = futex_hash(&key1);
- hb2 = futex_hash(&key2);
-
-retry_private:
- double_lock_hb(hb1, hb2);
- op_ret = futex_atomic_op_inuser(op, uaddr2);
- if (unlikely(op_ret < 0)) {
- double_unlock_hb(hb1, hb2);
-
- if (!IS_ENABLED(CONFIG_MMU) ||
- unlikely(op_ret != -EFAULT && op_ret != -EAGAIN)) {
- /*
- * we don't get EFAULT from MMU faults if we don't have
- * an MMU, but we might get them from range checking
- */
- ret = op_ret;
- return ret;
- }
-
- if (op_ret == -EFAULT) {
- ret = fault_in_user_writeable(uaddr2);
- if (ret)
- return ret;
- }
-
- cond_resched();
- if (!(flags & FLAGS_SHARED))
- goto retry_private;
- goto retry;
- }
-
- plist_for_each_entry_safe(this, next, &hb1->chain, list) {
- if (futex_match (&this->key, &key1)) {
- if (this->pi_state || this->rt_waiter) {
- ret = -EINVAL;
- goto out_unlock;
- }
- futex_wake_mark(&wake_q, this);
- if (++ret >= nr_wake)
- break;
- }
- }
-
- if (op_ret > 0) {
- op_ret = 0;
- plist_for_each_entry_safe(this, next, &hb2->chain, list) {
- if (futex_match (&this->key, &key2)) {
- if (this->pi_state || this->rt_waiter) {
- ret = -EINVAL;
- goto out_unlock;
- }
- futex_wake_mark(&wake_q, this);
- if (++op_ret >= nr_wake2)
- break;
- }
- }
- ret += op_ret;
- }
-
-out_unlock:
- double_unlock_hb(hb1, hb2);
- wake_up_q(&wake_q);
- return ret;
-}
-
/* The key must be already stored in q->key. */
struct futex_hash_bucket *futex_q_lock(struct futex_q *q)
__acquires(&hb->lock)
@@ -890,25 +565,6 @@ void __futex_queue(struct futex_q *q, struct futex_hash_bucket *hb)
}
/**
- * futex_queue() - Enqueue the futex_q on the futex_hash_bucket
- * @q: The futex_q to enqueue
- * @hb: The destination hash bucket
- *
- * The hb->lock must be held by the caller, and is released here. A call to
- * futex_queue() is typically paired with exactly one call to futex_unqueue(). The
- * exceptions involve the PI related operations, which may use futex_unqueue_pi()
- * or nothing if the unqueue is done as part of the wake process and the unqueue
- * state is implicit in the state of woken task (see futex_wait_requeue_pi() for
- * an example).
- */
-static inline void futex_queue(struct futex_q *q, struct futex_hash_bucket *hb)
- __releases(&hb->lock)
-{
- __futex_queue(q, hb);
- spin_unlock(&hb->lock);
-}
-
-/**
* futex_unqueue() - Remove the futex_q from its futex_hash_bucket
* @q: The futex_q to unqueue
*
@@ -919,7 +575,7 @@ static inline void futex_queue(struct futex_q *q, struct futex_hash_bucket *hb)
* - 1 - if the futex_q was still queued (and we removed unqueued it);
* - 0 - if the futex_q was already removed by the waking thread
*/
-static int futex_unqueue(struct futex_q *q)
+int futex_unqueue(struct futex_q *q)
{
spinlock_t *lock_ptr;
int ret = 0;
@@ -975,196 +631,6 @@ void futex_unqueue_pi(struct futex_q *q)
q->pi_state = NULL;
}
-static long futex_wait_restart(struct restart_block *restart);
-
-/**
- * futex_wait_queue() - futex_queue() and wait for wakeup, timeout, or signal
- * @hb: the futex hash bucket, must be locked by the caller
- * @q: the futex_q to queue up on
- * @timeout: the prepared hrtimer_sleeper, or null for no timeout
- */
-void futex_wait_queue(struct futex_hash_bucket *hb, struct futex_q *q,
- struct hrtimer_sleeper *timeout)
-{
- /*
- * The task state is guaranteed to be set before another task can
- * wake it. set_current_state() is implemented using smp_store_mb() and
- * futex_queue() calls spin_unlock() upon completion, both serializing
- * access to the hash list and forcing another memory barrier.
- */
- set_current_state(TASK_INTERRUPTIBLE);
- futex_queue(q, hb);
-
- /* Arm the timer */
- if (timeout)
- hrtimer_sleeper_start_expires(timeout, HRTIMER_MODE_ABS);
-
- /*
- * If we have been removed from the hash list, then another task
- * has tried to wake us, and we can skip the call to schedule().
- */
- if (likely(!plist_node_empty(&q->list))) {
- /*
- * If the timer has already expired, current will already be
- * flagged for rescheduling. Only call schedule if there
- * is no timeout, or if it has yet to expire.
- */
- if (!timeout || timeout->task)
- freezable_schedule();
- }
- __set_current_state(TASK_RUNNING);
-}
-
-/**
- * futex_wait_setup() - Prepare to wait on a futex
- * @uaddr: the futex userspace address
- * @val: the expected value
- * @flags: futex flags (FLAGS_SHARED, etc.)
- * @q: the associated futex_q
- * @hb: storage for hash_bucket pointer to be returned to caller
- *
- * Setup the futex_q and locate the hash_bucket. Get the futex value and
- * compare it with the expected value. Handle atomic faults internally.
- * Return with the hb lock held on success, and unlocked on failure.
- *
- * Return:
- * - 0 - uaddr contains val and hb has been locked;
- * - <1 - -EFAULT or -EWOULDBLOCK (uaddr does not contain val) and hb is unlocked
- */
-int futex_wait_setup(u32 __user *uaddr, u32 val, unsigned int flags,
- struct futex_q *q, struct futex_hash_bucket **hb)
-{
- u32 uval;
- int ret;
-
- /*
- * Access the page AFTER the hash-bucket is locked.
- * Order is important:
- *
- * Userspace waiter: val = var; if (cond(val)) futex_wait(&var, val);
- * Userspace waker: if (cond(var)) { var = new; futex_wake(&var); }
- *
- * The basic logical guarantee of a futex is that it blocks ONLY
- * if cond(var) is known to be true at the time of blocking, for
- * any cond. If we locked the hash-bucket after testing *uaddr, that
- * would open a race condition where we could block indefinitely with
- * cond(var) false, which would violate the guarantee.
- *
- * On the other hand, we insert q and release the hash-bucket only
- * after testing *uaddr. This guarantees that futex_wait() will NOT
- * absorb a wakeup if *uaddr does not match the desired values
- * while the syscall executes.
- */
-retry:
- ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q->key, FUTEX_READ);
- if (unlikely(ret != 0))
- return ret;
-
-retry_private:
- *hb = futex_q_lock(q);
-
- ret = futex_get_value_locked(&uval, uaddr);
-
- if (ret) {
- futex_q_unlock(*hb);
-
- ret = get_user(uval, uaddr);
- if (ret)
- return ret;
-
- if (!(flags & FLAGS_SHARED))
- goto retry_private;
-
- goto retry;
- }
-
- if (uval != val) {
- futex_q_unlock(*hb);
- ret = -EWOULDBLOCK;
- }
-
- return ret;
-}
-
-int futex_wait(u32 __user *uaddr, unsigned int flags, u32 val, ktime_t *abs_time, u32 bitset)
-{
- struct hrtimer_sleeper timeout, *to;
- struct restart_block *restart;
- struct futex_hash_bucket *hb;
- struct futex_q q = futex_q_init;
- int ret;
-
- if (!bitset)
- return -EINVAL;
- q.bitset = bitset;
-
- to = futex_setup_timer(abs_time, &timeout, flags,
- current->timer_slack_ns);
-retry:
- /*
- * Prepare to wait on uaddr. On success, it holds hb->lock and q
- * is initialized.
- */
- ret = futex_wait_setup(uaddr, val, flags, &q, &hb);
- if (ret)
- goto out;
-
- /* futex_queue and wait for wakeup, timeout, or a signal. */
- futex_wait_queue(hb, &q, to);
-
- /* If we were woken (and unqueued), we succeeded, whatever. */
- ret = 0;
- if (!futex_unqueue(&q))
- goto out;
- ret = -ETIMEDOUT;
- if (to && !to->task)
- goto out;
-
- /*
- * We expect signal_pending(current), but we might be the
- * victim of a spurious wakeup as well.
- */
- if (!signal_pending(current))
- goto retry;
-
- ret = -ERESTARTSYS;
- if (!abs_time)
- goto out;
-
- restart = &current->restart_block;
- restart->futex.uaddr = uaddr;
- restart->futex.val = val;
- restart->futex.time = *abs_time;
- restart->futex.bitset = bitset;
- restart->futex.flags = flags | FLAGS_HAS_TIMEOUT;
-
- ret = set_restart_fn(restart, futex_wait_restart);
-
-out:
- if (to) {
- hrtimer_cancel(&to->timer);
- destroy_hrtimer_on_stack(&to->timer);
- }
- return ret;
-}
-
-
-static long futex_wait_restart(struct restart_block *restart)
-{
- u32 __user *uaddr = restart->futex.uaddr;
- ktime_t t, *tp = NULL;
-
- if (restart->futex.flags & FLAGS_HAS_TIMEOUT) {
- t = restart->futex.time;
- tp = &t;
- }
- restart->fn = do_no_restart_syscall;
-
- return (long)futex_wait(uaddr, restart->futex.flags,
- restart->futex.val, tp, restart->futex.bitset);
-}
-
-
/* Constants for the pending_op argument of handle_futex_death */
#define HANDLE_DEATH_PENDING true
#define HANDLE_DEATH_LIST false