SmartisanOS_Kernel_Source/kernel/futex.c at master · hhjack/SmartisanOS_Kernel_Source · GitHub

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* Fast Userspace Mutexes (which I call "Futexes!").

* (C) Rusty Russell, IBM 2002

* Generalized futexes, futex requeueing, misc fixes by Ingo Molnar

* Removed page pinning, fix privately mapped COW pages and other cleanups

* Robust futex support started by Ingo Molnar

* Thanks to Thomas Gleixner for suggestions, analysis and fixes.

* PI-futex support started by Ingo Molnar and Thomas Gleixner

* PRIVATE futexes by Eric Dumazet

* Requeue-PI support by Darren Hart <dvhltc@us.ibm.com>

* Copyright (C) IBM Corporation, 2009

* Thanks to Thomas Gleixner for conceptual design and careful reviews.

* Thanks to Ben LaHaise for yelling "hashed waitqueues" loudly

* enough at me, Linus for the original (flawed) idea, Matthew

* Kirkwood for proof-of-concept implementation.

* "The futexes are also cursed."

* "But they come in a choice of three flavours!"

* This program is free software; you can redistribute it and/or modify

* it under the terms of the GNU General Public License as published by

* the Free Software Foundation; either version 2 of the License, or

* (at your option) any later version.

* This program is distributed in the hope that it will be useful,

* but WITHOUT ANY WARRANTY; without even the implied warranty of

* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the

* GNU General Public License for more details.

* You should have received a copy of the GNU General Public License

* along with this program; if not, write to the Free Software

* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA

#include <linux/slab.h>

#include <linux/poll.h>

#include <linux/fs.h>

#include <linux/file.h>

#include <linux/jhash.h>

#include <linux/init.h>

#include <linux/futex.h>

#include <linux/mount.h>

#include <linux/pagemap.h>

#include <linux/syscalls.h>

#include <linux/signal.h>

#include <linux/export.h>

#include <linux/magic.h>

#include <linux/pid.h>

#include <linux/nsproxy.h>

#include <linux/ptrace.h>

#include <asm/futex.h>

#include "rtmutex_common.h"

int __read_mostly futex_cmpxchg_enabled;

#define FUTEX_HASHBITS (CONFIG_BASE_SMALL ? 4 : 8)

* Futex flags used to encode options to functions and preserve them across

* restarts.

#define FLAGS_SHARED 0x01

#define FLAGS_CLOCKRT 0x02

#define FLAGS_HAS_TIMEOUT 0x04

* Priority Inheritance state:

struct futex_pi_state {

* list of 'owned' pi_state instances - these have to be

* cleaned up in do_exit() if the task exits prematurely:

struct list_head list;

* The PI object:

struct rt_mutex pi_mutex;

struct task_struct *owner;

atomic_t refcount;

union futex_key key;

};

/**

* struct futex_q - The hashed futex queue entry, one per waiting task

* @list: priority-sorted list of tasks waiting on this futex

* @task: the task waiting on the futex

* @lock_ptr: the hash bucket lock

* @key: the key the futex is hashed on

* @pi_state: optional priority inheritance state

* @rt_waiter: rt_waiter storage for use with requeue_pi

* @requeue_pi_key: the requeue_pi target futex key

* @bitset: bitset for the optional bitmasked wakeup

* We use this hashed waitqueue, instead of a normal wait_queue_t, so

* we can wake only the relevant ones (hashed queues may be shared).

* A futex_q has a woken state, just like tasks have TASK_RUNNING.

* It is considered woken when plist_node_empty(&q->list) || q->lock_ptr == 0.

* The order of wakeup is always to make the first condition true, then

* the second.

* PI futexes are typically woken before they are removed from the hash list via

* the rt_mutex code. See unqueue_me_pi().

struct futex_q {

struct plist_node list;

struct task_struct *task;

spinlock_t *lock_ptr;

union futex_key key;

struct futex_pi_state *pi_state;

struct rt_mutex_waiter *rt_waiter;

union futex_key *requeue_pi_key;

u32 bitset;

};

static const struct futex_q futex_q_init = {

/* list gets initialized in queue_me()*/

.key = FUTEX_KEY_INIT,

.bitset = FUTEX_BITSET_MATCH_ANY

};

* Hash buckets are shared by all the futex_keys that hash to the same

* location. Each key may have multiple futex_q structures, one for each task

* waiting on a futex.

struct futex_hash_bucket {

spinlock_t lock;

struct plist_head chain;

};

static struct futex_hash_bucket futex_queues[1<<FUTEX_HASHBITS];

* We hash on the keys returned from get_futex_key (see below).

static struct futex_hash_bucket *hash_futex(union futex_key *key)

{

u32 hash = jhash2((u32*)&key->both.word,

(sizeof(key->both.word)+sizeof(key->both.ptr))/4,

key->both.offset);

return &futex_queues[hash & ((1 << FUTEX_HASHBITS)-1)];

}

* Return 1 if two futex_keys are equal, 0 otherwise.

static inline int match_futex(union futex_key *key1, union futex_key *key2)

{

return (key1 && key2

&& key1->both.word == key2->both.word

&& key1->both.ptr == key2->both.ptr

&& key1->both.offset == key2->both.offset);

}

* Take a reference to the resource addressed by a key.

* Can be called while holding spinlocks.

static void get_futex_key_refs(union futex_key *key)

{

if (!key->both.ptr)

return;

switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {

case FUT_OFF_INODE:

ihold(key->shared.inode);

break;

case FUT_OFF_MMSHARED:

atomic_inc(&key->private.mm->mm_count);

break;

}

* Drop a reference to the resource addressed by a key.

* The hash bucket spinlock must not be held.

static void drop_futex_key_refs(union futex_key *key)

{

if (!key->both.ptr) {

/* If we're here then we tried to put a key we failed to get */

WARN_ON_ONCE(1);

return;

}

switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {

case FUT_OFF_INODE:

iput(key->shared.inode);

break;

case FUT_OFF_MMSHARED:

mmdrop(key->private.mm);

break;

}

/**

* get_futex_key() - Get parameters which are the keys for a futex

* @uaddr: virtual address of the futex

* @fshared: 0 for a PROCESS_PRIVATE futex, 1 for PROCESS_SHARED

* @key: address where result is stored.

* @rw: mapping needs to be read/write (values: VERIFY_READ,

* VERIFY_WRITE)

* Returns a negative error code or 0

* The key words are stored in *key on success.

* For shared mappings, it's (page->index, vma->vm_file->f_path.dentry->d_inode,

* offset_within_page). For private mappings, it's (uaddr, current->mm).

* We can usually work out the index without swapping in the page.

* lock_page() might sleep, the caller should not hold a spinlock.

static int

get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key, int rw)

{

unsigned long address = (unsigned long)uaddr;

struct mm_struct *mm = current->mm;

struct page *page, *page_head;

int err, ro = 0;

* The futex address must be "naturally" aligned.

key->both.offset = address % PAGE_SIZE;

if (unlikely((address % sizeof(u32)) != 0))

return -EINVAL;

address -= key->both.offset;

* PROCESS_PRIVATE futexes are fast.

* As the mm cannot disappear under us and the 'key' only needs

* virtual address, we dont even have to find the underlying vma.

* Note : We do have to check 'uaddr' is a valid user address,

* but access_ok() should be faster than find_vma()

if (!fshared) {

if (unlikely(!access_ok(VERIFY_WRITE, uaddr, sizeof(u32))))

return -EFAULT;

key->private.mm = mm;

key->private.address = address;

get_futex_key_refs(key);

return 0;

}

again:

err = get_user_pages_fast(address, 1, 1, &page);

* If write access is not required (eg. FUTEX_WAIT), try

* and get read-only access.

if (err == -EFAULT && rw == VERIFY_READ) {

err = get_user_pages_fast(address, 1, 0, &page);

ro = 1;

}

if (err < 0)

return err;

else

err = 0;

#ifdef CONFIG_TRANSPARENT_HUGEPAGE

page_head = page;

if (unlikely(PageTail(page))) {

put_page(page);

/* serialize against __split_huge_page_splitting() */

local_irq_disable();

if (likely(__get_user_pages_fast(address, 1, 1, &page) == 1)) {

page_head = compound_head(page);

* page_head is valid pointer but we must pin

* it before taking the PG_lock and/or

* PG_compound_lock. The moment we re-enable

* irqs __split_huge_page_splitting() can

* return and the head page can be freed from

* under us. We can't take the PG_lock and/or

* PG_compound_lock on a page that could be

* freed from under us.

if (page != page_head) {

get_page(page_head);

put_page(page);

}

local_irq_enable();

} else {

local_irq_enable();

goto again;

}

#else

page_head = compound_head(page);

if (page != page_head) {

get_page(page_head);

put_page(page);

}

#endif

lock_page(page_head);

* If page_head->mapping is NULL, then it cannot be a PageAnon

* page; but it might be the ZERO_PAGE or in the gate area or

* in a special mapping (all cases which we are happy to fail);

* or it may have been a good file page when get_user_pages_fast

* found it, but truncated or holepunched or subjected to

* invalidate_complete_page2 before we got the page lock (also

* cases which we are happy to fail). And we hold a reference,

* so refcount care in invalidate_complete_page's remove_mapping

* prevents drop_caches from setting mapping to NULL beneath us.

* The case we do have to guard against is when memory pressure made

* shmem_writepage move it from filecache to swapcache beneath us:

* an unlikely race, but we do need to retry for page_head->mapping.

if (!page_head->mapping) {

int shmem_swizzled = PageSwapCache(page_head);

unlock_page(page_head);

put_page(page_head);

if (shmem_swizzled)

goto again;

return -EFAULT;

}

* Private mappings are handled in a simple way.

* NOTE: When userspace waits on a MAP_SHARED mapping, even if

* it's a read-only handle, it's expected that futexes attach to

* the object not the particular process.

if (PageAnon(page_head)) {

* A RO anonymous page will never change and thus doesn't make

* sense for futex operations.

if (ro) {

err = -EFAULT;

goto out;

}

key->both.offset |= FUT_OFF_MMSHARED; /* ref taken on mm */

key->private.mm = mm;

key->private.address = address;

} else {

key->both.offset |= FUT_OFF_INODE; /* inode-based key */

key->shared.inode = page_head->mapping->host;

key->shared.pgoff = page_head->index;

}

get_futex_key_refs(key);

out:

unlock_page(page_head);

put_page(page_head);

return err;

}

static inline void put_futex_key(union futex_key *key)

{

drop_futex_key_refs(key);

}

/**

* fault_in_user_writeable() - Fault in user address and verify RW access

* @uaddr: pointer to faulting user space address

* Slow path to fixup the fault we just took in the atomic write

* access to @uaddr.

* We have no generic implementation of a non-destructive write to the

* user address. We know that we faulted in the atomic pagefault

* disabled section so we can as well avoid the #PF overhead by

* calling get_user_pages() right away.

static int fault_in_user_writeable(u32 __user *uaddr)

{

struct mm_struct *mm = current->mm;

int ret;

down_read(&mm->mmap_sem);

ret = fixup_user_fault(current, mm, (unsigned long)uaddr,

FAULT_FLAG_WRITE);

up_read(&mm->mmap_sem);

return ret < 0 ? ret : 0;

}

/**

* futex_top_waiter() - Return the highest priority waiter on a futex

* @hb: the hash bucket the futex_q's reside in

* @key: the futex key (to distinguish it from other futex futex_q's)

* Must be called with the hb lock held.

static struct futex_q *futex_top_waiter(struct futex_hash_bucket *hb,

union futex_key *key)

{

struct futex_q *this;

plist_for_each_entry(this, &hb->chain, list) {

if (match_futex(&this->key, key))

return this;

}

return NULL;

}

static int cmpxchg_futex_value_locked(u32 *curval, u32 __user *uaddr,

u32 uval, u32 newval)

{

int ret;

pagefault_disable();

ret = futex_atomic_cmpxchg_inatomic(curval, uaddr, uval, newval);

pagefault_enable();

return ret;

}

static int get_futex_value_locked(u32 *dest, u32 __user *from)

{

int ret;

pagefault_disable();

ret = __copy_from_user_inatomic(dest, from, sizeof(u32));

pagefault_enable();

return ret ? -EFAULT : 0;

}

* PI code:

static int refill_pi_state_cache(void)

{

struct futex_pi_state *pi_state;

if (likely(current->pi_state_cache))

return 0;

pi_state = kzalloc(sizeof(*pi_state), GFP_KERNEL);

if (!pi_state)

return -ENOMEM;

INIT_LIST_HEAD(&pi_state->list);

/* pi_mutex gets initialized later */

pi_state->owner = NULL;

atomic_set(&pi_state->refcount, 1);

pi_state->key = FUTEX_KEY_INIT;

current->pi_state_cache = pi_state;

return 0;

}

static struct futex_pi_state * alloc_pi_state(void)

{

struct futex_pi_state *pi_state = current->pi_state_cache;

WARN_ON(!pi_state);

current->pi_state_cache = NULL;

return pi_state;

}

static void free_pi_state(struct futex_pi_state *pi_state)

{

if (!atomic_dec_and_test(&pi_state->refcount))

return;

* If pi_state->owner is NULL, the owner is most probably dying

* and has cleaned up the pi_state already

if (pi_state->owner) {

raw_spin_lock_irq(&pi_state->owner->pi_lock);

list_del_init(&pi_state->list);

raw_spin_unlock_irq(&pi_state->owner->pi_lock);

rt_mutex_proxy_unlock(&pi_state->pi_mutex, pi_state->owner);

}

if (current->pi_state_cache)

kfree(pi_state);

else {

* pi_state->list is already empty.

* clear pi_state->owner.

* refcount is at 0 - put it back to 1.

pi_state->owner = NULL;

atomic_set(&pi_state->refcount, 1);

current->pi_state_cache = pi_state;

}

* Look up the task based on what TID userspace gave us.

* We dont trust it.

static struct task_struct * futex_find_get_task(pid_t pid)

{

struct task_struct *p;

rcu_read_lock();

p = find_task_by_vpid(pid);

if (p)

get_task_struct(p);

rcu_read_unlock();

return p;

}

* This task is holding PI mutexes at exit time => bad.

* Kernel cleans up PI-state, but userspace is likely hosed.

* (Robust-futex cleanup is separate and might save the day for userspace.)

void exit_pi_state_list(struct task_struct *curr)

{

struct list_head *next, *head = &curr->pi_state_list;

struct futex_pi_state *pi_state;

struct futex_hash_bucket *hb;

union futex_key key = FUTEX_KEY_INIT;

if (!futex_cmpxchg_enabled)

return;

* We are a ZOMBIE and nobody can enqueue itself on

* pi_state_list anymore, but we have to be careful

* versus waiters unqueueing themselves:

raw_spin_lock_irq(&curr->pi_lock);

while (!list_empty(head)) {

next = head->next;

pi_state = list_entry(next, struct futex_pi_state, list);

key = pi_state->key;

hb = hash_futex(&key);

raw_spin_unlock_irq(&curr->pi_lock);

spin_lock(&hb->lock);

raw_spin_lock_irq(&curr->pi_lock);

* We dropped the pi-lock, so re-check whether this

* task still owns the PI-state:

if (head->next != next) {

spin_unlock(&hb->lock);

continue;

}

WARN_ON(pi_state->owner != curr);

WARN_ON(list_empty(&pi_state->list));

list_del_init(&pi_state->list);

pi_state->owner = NULL;

raw_spin_unlock_irq(&curr->pi_lock);

rt_mutex_unlock(&pi_state->pi_mutex);

spin_unlock(&hb->lock);

raw_spin_lock_irq(&curr->pi_lock);

}

raw_spin_unlock_irq(&curr->pi_lock);

}

static int

lookup_pi_state(u32 uval, struct futex_hash_bucket *hb,

union futex_key *key, struct futex_pi_state **ps)

{

struct futex_pi_state *pi_state = NULL;

struct futex_q *this, *next;

struct plist_head *head;

struct task_struct *p;

pid_t pid = uval & FUTEX_TID_MASK;

head = &hb->chain;

plist_for_each_entry_safe(this, next, head, list) {

if (match_futex(&this->key, key)) {

* Another waiter already exists - bump up

* the refcount and return its pi_state:

pi_state = this->pi_state;

* Userspace might have messed up non-PI and PI futexes

if (unlikely(!pi_state))

return -EINVAL;

WARN_ON(!atomic_read(&pi_state->refcount));

* When pi_state->owner is NULL then the owner died

* and another waiter is on the fly. pi_state->owner

* is fixed up by the task which acquires

* pi_state->rt_mutex.

* We do not check for pid == 0 which can happen when

* the owner died and robust_list_exit() cleared the

* TID.

if (pid && pi_state->owner) {

* Bail out if user space manipulated the

* futex value.

if (pid != task_pid_vnr(pi_state->owner))

return -EINVAL;

}

atomic_inc(&pi_state->refcount);

*ps = pi_state;

return 0;

}

* We are the first waiter - try to look up the real owner and attach

* the new pi_state to it, but bail out when TID = 0

if (!pid)

return -ESRCH;

p = futex_find_get_task(pid);

if (!p)

return -ESRCH;

* We need to look at the task state flags to figure out,

* whether the task is exiting. To protect against the do_exit

* change of the task flags, we do this protected by

* p->pi_lock:

raw_spin_lock_irq(&p->pi_lock);

if (unlikely(p->flags & PF_EXITING)) {

* The task is on the way out. When PF_EXITPIDONE is

* set, we know that the task has finished the

* cleanup:

int ret = (p->flags & PF_EXITPIDONE) ? -ESRCH : -EAGAIN;

raw_spin_unlock_irq(&p->pi_lock);

put_task_struct(p);

return ret;

}

pi_state = alloc_pi_state();

* Initialize the pi_mutex in locked state and make 'p'

* the owner of it:

rt_mutex_init_proxy_locked(&pi_state->pi_mutex, p);

/* Store the key for possible exit cleanups: */

pi_state->key = *key;

WARN_ON(!list_empty(&pi_state->list));

list_add(&pi_state->list, &p->pi_state_list);

pi_state->owner = p;

raw_spin_unlock_irq(&p->pi_lock);

put_task_struct(p);

*ps = pi_state;

return 0;

}

/**

* futex_lock_pi_atomic() - Atomic work required to acquire a pi aware futex

* @uaddr: the pi futex user address

* @hb: the pi futex hash bucket

* @key: the futex key associated with uaddr and hb

* @ps: the pi_state pointer where we store the result of the

* lookup

* @task: the task to perform the atomic lock work for. This will

* be "current" except in the case of requeue pi.

* @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0)

* Returns:

* 0 - ready to wait

* 1 - acquired the lock

* <0 - error

* The hb->lock and futex_key refs shall be held by the caller.

static int futex_lock_pi_atomic(u32 __user *uaddr, struct futex_hash_bucket *hb,

union futex_key *key,

struct futex_pi_state **ps,

struct task_struct *task, int set_waiters)

{

int lock_taken, ret, ownerdied = 0;

u32 uval, newval, curval, vpid = task_pid_vnr(task);

retry:

ret = lock_taken = 0;

* To avoid races, we attempt to take the lock here again

* (by doing a 0 -> TID atomic cmpxchg), while holding all

* the locks. It will most likely not succeed.

newval = vpid;

if (set_waiters)

newval |= FUTEX_WAITERS;

if (unlikely(cmpxchg_futex_value_locked(&curval, uaddr, 0, newval)))

return -EFAULT;

* Detect deadlocks.

if ((unlikely((curval & FUTEX_TID_MASK) == vpid)))

return -EDEADLK;

* Surprise - we got the lock. Just return to userspace:

if (unlikely(!curval))

return 1;

uval = curval;

* Set the FUTEX_WAITERS flag, so the owner will know it has someone

* to wake at the next unlock.

newval = curval | FUTEX_WAITERS;

* There are two cases, where a futex might have no owner (the

* owner TID is 0): OWNER_DIED. We take over the futex in this

* case. We also do an unconditional take over, when the owner

* of the futex died.

* This is safe as we are protected by the hash bucket lock !

if (unlikely(ownerdied || !(curval & FUTEX_TID_MASK))) {

/* Keep the OWNER_DIED bit */

newval = (curval & ~FUTEX_TID_MASK) | vpid;

ownerdied = 0;

lock_taken = 1;

}

if (unlikely(cmpxchg_futex_value_locked(&curval, uaddr, uval, newval)))

return -EFAULT;

if (unlikely(curval != uval))

goto retry;

* We took the lock due to owner died take over.

if (unlikely(lock_taken))

return 1;

* We dont have the lock. Look up the PI state (or create it if

* we are the first waiter):

ret = lookup_pi_state(uval, hb, key, ps);

if (unlikely(ret)) {

switch (ret) {

case -ESRCH:

* No owner found for this futex. Check if the

* OWNER_DIED bit is set to figure out whether

* this is a robust futex or not.

if (get_futex_value_locked(&curval, uaddr))

return -EFAULT;

* We simply start over in case of a robust

* futex. The code above will take the futex

* and return happy.

if (curval & FUTEX_OWNER_DIED) {

ownerdied = 1;

goto retry;

}

default:

break;

}

return ret;

}

/**

* __unqueue_futex() - Remove the futex_q from its futex_hash_bucket

* @q: The futex_q to unqueue

* The q->lock_ptr must not be NULL and must be held by the caller.

static void __unqueue_futex(struct futex_q *q)

{

struct futex_hash_bucket *hb;

if (WARN_ON_SMP(!q->lock_ptr || !spin_is_locked(q->lock_ptr))

|| WARN_ON(plist_node_empty(&q->list)))

return;

hb = container_of(q->lock_ptr, struct futex_hash_bucket, lock);

plist_del(&q->list, &hb->chain);

}

* The hash bucket lock must be held when this is called.

* Afterwards, the futex_q must not be accessed.

static void wake_futex(struct futex_q *q)

{

struct task_struct *p = q->task;

* We set q->lock_ptr = NULL _before_ we wake up the task. If

* a non-futex wake up happens on another CPU then the task

* might exit and p would dereference a non-existing task

* struct. Prevent this by holding a reference on p across the

* wake up.

get_task_struct(p);

__unqueue_futex(q);

* The waiting task can free the futex_q as soon as

* q->lock_ptr = NULL is written, without taking any locks. A

* memory barrier is required here to prevent the following

* store to lock_ptr from getting ahead of the plist_del.

smp_wmb();

q->lock_ptr = NULL;

wake_up_state(p, TASK_NORMAL);

put_task_struct(p);

}

static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_q *this)

{

struct task_struct *new_owner;

struct futex_pi_state *pi_state = this->pi_state;

u32 uninitialized_var(curval), newval;

if (!pi_state)

return -EINVAL;

* If current does not own the pi_state then the futex is

* inconsistent and user space fiddled with the futex value.

if (pi_state->owner != current)

return -EINVAL;

raw_spin_lock(&pi_state->pi_mutex.wait_lock);

new_owner = rt_mutex_next_owner(&pi_state->pi_mutex);

* It is possible that the next waiter (the one that brought

* this owner to the kernel) timed out and is no longer

* waiting on the lock.

if (!new_owner)

new_owner = this->task;

* We pass it to the next owner. (The WAITERS bit is always

* kept enabled while there is PI state around. We must also

* preserve the owner died bit.)

if (!(uval & FUTEX_OWNER_DIED)) {

int ret = 0;

newval = FUTEX_WAITERS | task_pid_vnr(new_owner);

if (cmpxchg_futex_value_locked(&curval, uaddr, uval, newval))

ret = -EFAULT;

else if (curval != uval)

ret = -EINVAL;

if (ret) {

raw_spin_unlock(&pi_state->pi_mutex.wait_lock);

return ret;

}

raw_spin_lock_irq(&pi_state->owner->pi_lock);

WARN_ON(list_empty(&pi_state->list));

list_del_init(&pi_state->list);

raw_spin_unlock_irq(&pi_state->owner->pi_lock);

raw_spin_lock_irq(&new_owner->pi_lock);

WARN_ON(!list_empty(&pi_state->list));

list_add(&pi_state->list, &new_owner->pi_state_list);

pi_state->owner = new_owner;

raw_spin_unlock_irq(&new_owner->pi_lock);

raw_spin_unlock(&pi_state->pi_mutex.wait_lock);

rt_mutex_unlock(&pi_state->pi_mutex);

return 0;

}

static int unlock_futex_pi(u32 __user *uaddr, u32 uval)

{

u32 uninitialized_var(oldval);

* There is no waiter, so we unlock the futex. The owner died

* bit has not to be preserved here. We are the owner:

if (cmpxchg_futex_value_locked(&oldval, uaddr, uval, 0))

return -EFAULT;

if (oldval != uval)

return -EAGAIN;

return 0;

}

* Express the locking dependencies for lockdep:

static inline void

double_lock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)

{

if (hb1 <= hb2) {

spin_lock(&hb1->lock);

if (hb1 < hb2)

spin_lock_nested(&hb2->lock, SINGLE_DEPTH_NESTING);

} else { /* hb1 > hb2 */

spin_lock(&hb2->lock);

spin_lock_nested(&hb1->lock, SINGLE_DEPTH_NESTING);

}

static inline void

double_unlock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)

{

spin_unlock(&hb1->lock);

if (hb1 != hb2)

spin_unlock(&hb2->lock);

}

* Wake up waiters matching bitset queued on this futex (uaddr).

static int

futex_wake(u32 __user *uaddr, unsigned int flags, int nr_wake, u32 bitset)

{

struct futex_hash_bucket *hb;

struct futex_q *this, *next;

struct plist_head *head;

union futex_key key = FUTEX_KEY_INIT;

int ret;

if (!bitset)

return -EINVAL;

ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, VERIFY_READ);

if (unlikely(ret != 0))

goto out;

hb = hash_futex(&key);

spin_lock(&hb->lock);

head = &hb->chain;

plist_for_each_entry_safe(this, next, head, list) {

if (match_futex (&this->key, &key)) {

if (this->pi_state || this->rt_waiter) {

ret = -EINVAL;

break;

}

/* Check if one of the bits is set in both bitsets */

View remainder of file in raw view

SmartisanOS_Kernel_Source/kernel/futex.c at master · hhjack/SmartisanOS_Kernel_Source · GitHub

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